Hello everyone
Have you ever lain in bed at night, tortured by your unrequited dreams of making a random tremolo pedal that will screw your audio signal up in a variety of uncontrollable chaotic ways? While using very few parts? You have? Well, I am about to make your day :)
For the first time in how ever many years I've been on this forum I am about to astound / impress / surprise you by actually designing my first circuit (instead of asking for help after I break other people's designs). I've made a random stuttering tremolo. It actually works. I was wondering how to get a random tremolo effect and was looking at circuits where clever people use microprocessors to generate randomness that modulates the brightness of LED / LDR combos but that was too smart for my limited brain. And I thought, how can I, a man of extremely limited electrical knowledge realise my dreams? By cheating of course! All I needed was an LED that already had a random flicker to it... yes you guessed it, those really tragic candle flame LEDs! They are perfect (well they'll do for a start anyway). So this is the nearest I will probably ever get to creative genius :) You saw it first folks!
Hopefully the below link goes to an mp3 of me gently playing and gradually adjusting the one pot on the circuit to remove more and more audio. This recording only has two LEDs / LDRs in it (I've run out of a lot of parts recently and had to wait to today to get paid before I could order more, so the next iteration of this will have 4 LED/LDRs, each with their own pot to control the amount of sound they erode.) The circuit works with two homademade vactrols, so I'm sure it will work with 4!
https://drive.google.com/file/d/1OTF2-Z9_XFuKUvo3IM4qoyw9OXyUtqnT/view?usp=sharing (https://drive.google.com/file/d/1OTF2-Z9_XFuKUvo3IM4qoyw9OXyUtqnT/view?usp=sharing)
Schematic for your amusement.
(https://i.imgur.com/pIOoW38.png)
The pot starves the LEDs of power (the 78L05 is there to stop the LEDs exploding; it's hard to find any datasheets for these flicker LEDs - all of which came from random ebay sellers - and the one I did find said they shouldn't be fed more than 5V, so that's what I've done). I originally had a 100ohm resistor just after the 78L05 because I thought there should be a little extra protection, but it got so hot that I swapped it for a 470ohm... so the maximum brightness is dimmed a little, but the resistor no longer burns my skin if I touch it! The voltage starving doesn't change the rate the LEDs flicker at sadly (in the above mp3 I'm using a slow change RGB disco LED and a bright green candle flicker LED) I've not been able to achieve that at all, but with less current some of the colours of the RGB LEDs no longer light up so that adds variety to the tremolo, or with the standard candle LEDs they tend to turn off more and struggle to light up which adds sawtooth to the tremolo. I have found that two of the same LEDs can be used with a different LDR each - if they both get powered on at the same time they stay identical in their flicker timing for a few seconds and then slowly drift apart. I'm not sure if there is a way to 'boot' multiple LEDs of the same type with different start times to make the tremolo pattern even more unique... so that might be something interesting to explore if you only have one type of candle flame LED.
I've tried four different LEDs. The traditional orange LED candle flame is the least interesting - it rarely turns off and modulates too gently. I discovered that it can be made more interesting (audio wise) if you put a standard red LED in series after it - the orange LED then loses current to the red LED, causing it to stutter much more and make interesting patterns. The bright green candle LED gives smooth slow volume undulations, the slow RGB Disco LED (which is not slow) makes the fast patterns and gets more chaotic as it is starved, and a slow RGB colour change LED is not so interesting with full current but becomes more random with less current because it is unable to generate some of the colours in the spectrum and so turns off at times.
I added a 10K resistor after the input audio jack because I think Duck got me to do that on a previous circuit although I can't remember why it was important...sorry Duck.
Any thoughts about stuff I should add to this circuit to make it work better / different / be friends with other pedals etc would be great. A way to cut down the background hum when the audio is cut out? This is only on breadboard at the moment with insulation tape wrapped around the vactrols (and recorded with the lights off) so there is bound to be some light leakage at present, so this might disappear if things are soldered together.
Stuff to do - add a boost circuit after the LDRs and before the audio out jack (probably a DOD 210 preamp - they are tiny!). Maybe add a blend pot so that there is always some original audio to be mixed in? Add a switch to each LDR to take them in and out of the circuit as desired and a pot for each LED so they can be starved at different amounts. It's a shame they have to be kept inside a box for the final version; they look like a crazy disco rave migraine inducing light pattern at the moment! Maybe it's better that way...
If anyone knows a way to make these LEDs actually change the rate they modulate at I would be very grateful. I've tried adding capacitors to ground from the LEDs (thinking that I've used caps to slow down tremolos before) but that did nothing, and I can't find any info about this online.
Enjoy your weekend!
Cute!
This won't help you. But in the 1970s I ran an ARP 2500 synth with very good random voltage, including a heavily high-cut filtered rumble/wobble. Run that to a VCA (or VCO) and you got your random modulation. Not a lot of control of "speed" unless you added a filter. (In your scheme this filter has to be a light-filter and that's not a stock part.)
http://www.guitarfool.com/ARP2500/1016.html
http://www.guitarfool.com/ARP2500/1036.html
https://youtu.be/ZNa-JHPnpgM?t=127
That is the coolest thing ever. 8) 8) 8) Or at least, the coolest thing this Saturday. So far...
May I be so bold as to suggest a name for this wonder of engineering?
The Moidulator!
Quote from: PRR on August 30, 2024, 10:44:54 PMCute!
This won't help you. But in the 1970s I ran an ARP 2500 synth with very good random voltage, including a heavily high-cut filtered rumble/wobble. Run that to a VCA (or VCO) and you got your random modulation. Not a lot of control of "speed" unless you added a filter. (In your scheme this filter has to be a light-filter and that's not a stock part.)
http://www.guitarfool.com/ARP2500/1016.html
http://www.guitarfool.com/ARP2500/1036.html
Thanks! Glad you like it :)
Wow, an ARP synth is one of those pieces of kit I would love to play with. Those schematics you posted links to are just a bit
too complex for me at the moment though! I've got more ideas to adjust this circuit so I'm reading up about them to see if they sound plausible and will hopefully get built at some point in hte distant future... I need to get on with this circuit first!
Quote from: bluebunny on August 31, 2024, 04:48:16 AMThat is the coolest thing ever. 8) 8) 8) Or at least, the coolest thing this Saturday. So far...
May I be so bold as to suggest a name for this wonder of engineering?
The Moidulator!
Thanks Marc :) I will admit I was totally astounded with myself that this actually worked (and first time) and yes I did indeed think it was one of the coolest things to ever happen to me. I have to say your naming idea is both flattering and genius! I think it has to be! I have some plans for a more complex version of this circuit which sound great in my head, and if that ever gets made it can be the Son of Moidulator! Thanks for your suggestion. Hopefully I can get some time tomorrow to update the circuit - I added a third LED/LDR combo and that worked, and it sounds better than the two LED/LDR version I posted above.
I am thinking I need to get rid of the background hum if possible, and also try different LDR types... the best ones so far are some unlabelled random bag I got from Ebay years ago that I don't really know what spec they are. I've tried some 9K - 20K and some 9K - 24K LDRs and they didn't work so well - I think I need to find an LDR with a much lower bright range 1K - 20k? something liike that to get the most contrast between audio on and off based on LED brightness. Time to read through some data sheets I guess. I was wondering whether it was worth placing a resistor in parallel with an LDR to lower its resistance, but I presume that would also lower the maximum resistanc when the LED is off as well, so that might not be the best way to approach the issue. Some thinking is required!
Do a couple voltage followers either end to buffer. You could mix in caps in series/to ground with your ldrs for lpfs and hpfs. Yes, parallel with the max resistance you want given a light tight Lee should have such high resistance it'll be about that; as an aficionado of cheap let, don't trust the info with them.
You can use negative feedback (I believe) to remove frequencies from the signal too. Once you add in op amps (properly biased) I'm sure you can go lots of ways!
Oh! Also a small current limiting resistor after the flickering led (trim pot instead?) could help adjust the on off ratios.
Since most of the cells are cadmium sulphide and most of the remaining ones are cadmium selenide, this could be difficult to find in the future as cadmium is one of the thsree RoHS banned metals (along with mercury and lead). There may be only a limited supply of these devices available.
From some admittedly old catalogs that only carried RCA and Philips photocells, the light to dark ratio was much greater than those moid was looking at. The RCA NSL62 is a 0.25 inch unit with a 100 footcandle resistance of 770 ohms, a 1 footcandle resistance of 28 Kohm and a dark resistance of 10 megohms. It may be that for tremolo frequencies, you can't get to the 10 megohm resistance in time but you should be able to get better than 9K - 20K with good light shielding.
I dunno nuffin baht these candles wot you speek of. but, we are told, when leds cycle, they have "circuitry" inside, and they are inherently noisy. it might be that you can't get them noise free.
but, we always tell, leds in parallel get a current limit resistor each, because they won't current share otherwise. that single 470R resistor might be what makes it all work, it might be what causes them buzzes. maybe those candle things don't need a current limit, who nose, not me.
but you could try a 470R in series with each of the led things, all connected back to the VR1 wiper. what's the worst could happen - smoked pot? burnt finger?
that's three buts.
Quote from: Matthew Sanford on August 31, 2024, 07:16:03 PMDo a couple voltage followers either end to buffer. You could mix in caps in series/to ground with your ldrs for lpfs and hpfs.
Thanks Matthew - do you mean adding something like a TL072 to the circuit so the audio would come from the jack in to the first opamp on the TL072, then pass through all the LED/LDR part of the circuit and before it hits the audio out jack, it would go through the second op amp on the TL072? Or have I got that totally confused? (quite possible!)
Quote from: Matthew Sanford on August 31, 2024, 07:16:03 PMYes, parallel with the max resistance you want given a light tight Lee should have such high resistance it'll be about that; as an aficionado of cheap let, don't trust the info with them.
Sorry I don't understand any of that, I think you just went way over my technical knowledge there!
Quote from: Matthew Sanford on August 31, 2024, 07:16:03 PMYou can use negative feedback (I believe) to remove frequencies from the signal too. Once you add in op amps (properly biased) I'm sure you can go lots of ways!
Oh! Also a small current limiting resistor after the flickering led (trim pot instead?) could help adjust the on off ratios.
That's interesting - I thought the CLR would go between the power and the flickering LED (like I have it at the moment) but you think it should go between the cathode of the LED and the ground of the circuit? Or do you mean in addition to the 470R I've got (that is in place because I was worrying about 5V going straight to an LED)
Quote from: amptramp on September 01, 2024, 09:24:30 AMSince most of the cells are cadmium sulphide and most of the remaining ones are cadmium selenide, this could be difficult to find in the future as cadmium is one of the thsree RoHS banned metals (along with mercury and lead). There may be only a limited supply of these devices available.
I had heard that LDRs are going to be difficult to find in future which is a real shame. I wonder if there will be anything to replace them?
Quote from: amptramp on September 01, 2024, 09:24:30 AMFrom some admittedly old catalogs that only carried RCA and Philips photocells, the light to dark ratio was much greater than those moid was looking at. The RCA NSL62 is a 0.25 inch unit with a 100 footcandle resistance of 770 ohms, a 1 footcandle resistance of 28 Kohm and a dark resistance of 10 megohms. It may be that for tremolo frequencies, you can't get to the 10 megohm resistance in time but you should be able to get better than 9K - 20K with good light shielding.
THanks Amptramp. Those values sound really good, however I couldn't find any mention of an NSL62 at any of the component stores (or even on ebay!) so I guess they are sadly long gone. I did spend some time looking at a lot of different LDRs and found three possible candidates to try that I can get from Mouser in the UK
NSL-6110 light resistance 1.34K - 2.66K, dark resistance 11M
NORPS-12 light resistance 5.4K - 12.6K, dark resistance 1M
NSL-06S53 light resistance 5.4K - 100K, dark resistance 20M
Do any of those sound promising? To me the NSL-6110 looks really good, but would it be worth buying samples of all of them? They're not cheap sadly (nothing like the GL series LDRs which can be bought for very small sums) and I need to order £33 worth of stuff to get free postage (but four of each of those LDRs is almost £30 so that's not too hard!)
Quote from: duck_arse on September 01, 2024, 10:57:39 AMI dunno nuffin baht these candles wot you speek of. but, we are told, when leds cycle, they have "circuitry" inside, and they are inherently noisy. it might be that you can't get them noise free.
Ahhh it never occured to me that that might be the issue - I was assuming it was the DC power on the breadboard... I thought it might be a good idea to add in some of the components that ElectricDruid puts in the power sections of his schematics? I noticed that his optical tremolo had a 78L05 in the power section so thought some of those components around it might be a good place to start:
(https://electricdruid.net/wp-content/uploads/2022/08/MiniTremSchematicPg1-1-1024x725.jpg)
Quote from: duck_arse on September 01, 2024, 10:57:39 AMbut, we always tell, leds in parallel get a current limit resistor each, because they won't current share otherwise. that single 470R resistor might be what makes it all work, it might be what causes them buzzes. maybe those candle things don't need a current limit, who nose, not me.
but you could try a 470R in series with each of the led things, all connected back to the VR1 wiper. what's the worst could happen - smoked pot? burnt finger?
that's three buts.
But I love the way you butt in! I will give that lot a try. I didn't know that LEDs in parallel needed CLRs each, so thanks for warning me. I think it's time to re-arrange the mess on my breadboard! I'll be back :)
One possibly interesting note - I was comparing recordings I made of the circuit with two and three LED/LDR combos in it, and the circuit with three LED/LDRs is less noisy than the one with two. When I get more parts I will try four of them! I've no idea why this should be, but maybe more = better in this case. The tremolo effect sounds more random with three LEDs that's for sure.
Quote from: moid on September 01, 2024, 05:03:45 PMAhhh it never occured to me that that might be the issue - I was assuming it was the DC power on the breadboard... I thought it might be a good idea to add in some of the components that ElectricDruid puts in the power sections of his schematics? I noticed that his optical tremolo had a 78L05 in the power section so thought some of those components around it might be a good place to start:
The reason for the 78L05 is that the LFO I used is a PIC microprocessor-based thing, the StompLFO. That needs 5V to run. There's no other reason for the 5V supply to be there, but since I *had* to have a separate power supply for the digital section of the circuit (the page you haven't shown (https://electricdruid.net/wp-content/uploads/2022/08/MiniTremPg2-scaled.jpg)) I used it for the LEDs and anything else not directly audio-related. Even so, I had trouble on the first version of the PCB because of ticking caused by ground currents. The solution was to separate the ground paths for the two sections too, so digital/LED ground currents don't flow in the same paths as the audio grounds.
Incidentally, I notice now that the schematic page you showed misleadingly says "1 of 1" instead of "1 of 2". My bad, sorry. That second page is important too!
HTH
For limiting ldr response, look at this snip Electric Druid's FilterFx (I hope Tom doesn't mind)
(https://i.postimg.cc/zVy5CX3w/IMG-3644.png) (https://postimg.cc/zVy5CX3w)
Actually look at the project page. (https://electricdruid.net/filterfx-lp-bp-hp-lfo-filter/) He references the thread here on it's development, good info on filtering and a great pedal was made! Yes on the TL072, coupling caps with bias voltage to + in and output tied to - in. See Druid schematics for the guidance that has led me, as you did for the power (good on ya). You could have global feedback or op amps through the middle, see the resonance and lp/bp/hp for example. I didn't see your clr, sorry, but you could put a 1k trimpot instead/in addition to play with different levels. And if you want volume tremelo, a voltage dividing output volume pot (1 to ground, 2 out, 3 to signal) with the ldr parallel with pins 1&2 (and turn it down a little to put some resistance the non-ldr side
I love it, brilliant out of the box new use! You might optocouple power to get led noise out, but I don't know how exactly
A few ideas:
1. You could try to arrange several light sources so they only need one LDR. Use some sort of small light tight container where you have an LDR in one spot. Then arrange all the flickering leds to point the brightest spot of their light towards the LDR.
2. Play around wiht the value of your R2. It should affect the depth of the effect, especially if you put a buffer or another effect in front of the Moidulator. With a passive guitar straight in to the R2 it might not make as big difference.
> It's a shame they have to be kept inside a box for the final version; they look like a crazy disco rave migraine inducing light pattern at the moment!
You could have two of each LED: one inside with its respective LDR, and one outside for the light-show! :icon_cool:
Quote from: moid on September 01, 2024, 05:03:45 PMQuote from: amptramp on September 01, 2024, 09:24:30 AMSince most of the cells are cadmium sulphide and most of the remaining ones are cadmium selenide, this could be difficult to find in the future as cadmium is one of the thsree RoHS banned metals (along with mercury and lead). There may be only a limited supply of these devices available.
I had heard that LDRs are going to be difficult to find in future which is a real shame. I wonder if there will be anything to replace them?
Chase Bliss have recently announced that they're dropping 5 pedals from their range because of vactrol problems. They're selling the remaining stock in the US, where this stuff isn't controlled yet.
I exchanged a few emails with Joel Korte at Chase Bliss, and it seems the catalyst for this is that the *UK* authorities are cracking down on vactrols. Although the UK left the EU (and so the EU's RoHS directive no longer applies in the UK) most EU environmental legislation was rolled-over into UK law on exit so that businesses didn't have a completely-changed legal framework to deal with overnight. He said he's been in contact with several UK pedalmakers who have also had problems.
Whether genuine non-cadmium LDRs are technically possible at some point in the future is a physical chemistry question that I'm not qualified to answer.
This is timely for me since I was about to order more vatrols for the Druid shop, but if the "RoHS" claim on those products is not actually true when independently tested then there's really no point, so I'm holding off until I've found out what the UK's Office of Product Safety and Standards has found out about vactrols.
I wonder if there would be a way for phototransistors to act as a replacement for LDR's as they're much easier to find and don't have the Cadmium that Europe doesn't like. I have a 3d printer and I'm planning on making my own vactrols with that (just to be less janky than shrink wrap and duct tape)
Phototransistors and LDR's are not really interchangeable but I'm sure things can be done circuitry wise to make it more similar
Quote from: ElectricDruid on September 01, 2024, 06:37:51 PMQuote from: moid on September 01, 2024, 05:03:45 PMAhhh it never occured to me that that might be the issue - I was assuming it was the DC power on the breadboard... I thought it might be a good idea to add in some of the components that ElectricDruid puts in the power sections of his schematics? I noticed that his optical tremolo had a 78L05 in the power section so thought some of those components around it might be a good place to start:
The reason for the 78L05 is that the LFO I used is a PIC microprocessor-based thing, the StompLFO. That needs 5V to run. There's no other reason for the 5V supply to be there, but since I *had* to have a separate power supply for the digital section of the circuit (the page you haven't shown (https://electricdruid.net/wp-content/uploads/2022/08/MiniTremPg2-scaled.jpg)) I used it for the LEDs and anything else not directly audio-related. Even so, I had trouble on the first version of the PCB because of ticking caused by ground currents. The solution was to separate the ground paths for the two sections too, so digital/LED ground currents don't flow in the same paths as the audio grounds.
Incidentally, I notice now that the schematic page you showed misleadingly says "1 of 1" instead of "1 of 2". My bad, sorry. That second page is important too!
HTH
Thanks Tom! In that case I might leave my 78L05 where it is and not add the other parts you did unless I get noise issues. I'm using the 78L05 bcause I found a datasheet for a candle flame LED that said that it should not be fed more than 5V, so I used that and a resistor to make sure nothing went bang!
It is going to be digital in the end. Go ahead and develop a GOOD ADC board, compute the optimum gain function, apply it to your bytes. Latency can be 20 MICROseconds which is quite short.
Hello everyone
Sorry about the delay in replying, term started up again and life got busy :( And then my asthma decided I should have a bad time on top. Yay. Anyway I finally got some new components and have made a new circuit (somewhere further down this thread) with new weird issues and questions to ask you chaps. I will answer the great posts you all made first though!
Quote from: Matthew Sanford on September 01, 2024, 06:53:54 PMFor limiting ldr response, look at this snip Electric Druid's FilterFx (I hope Tom doesn't mind)
(https://i.postimg.cc/zVy5CX3w/IMG-3644.png) (https://postimg.cc/zVy5CX3w)
Actually look at the project page. (https://electricdruid.net/filterfx-lp-bp-hp-lfo-filter/) He references the thread here on it's development, good info on filtering and a great pedal was made! Yes on the TL072, coupling caps with bias voltage to + in and output tied to - in. See Druid schematics for the guidance that has led me, as you did for the power (good on ya). You could have global feedback or op amps through the middle, see the resonance and lp/bp/hp for example. I didn't see your clr, sorry, but you could put a 1k trimpot instead/in addition to play with different levels. And if you want volume tremelo, a voltage dividing output volume pot (1 to ground, 2 out, 3 to signal) with the ldr parallel with pins 1&2 (and turn it down a little to put some resistance the non-ldr side
I love it, brilliant out of the box new use! You might optocouple power to get led noise out, but I don't know how exactly
Thanks Matthew! I don't think I want to limit the LDRs though, more maximise them? Or maybe I don't understand what you're telling me (sorry). Later down in this thread I will put a revised schematic (I rebuilt the circuit today) although that was to make it easier to adjust on breadboard and get more control in. I haven't got to your ideas yet. I really like the idea of the volume tremolo control but I don;t understand what you wrote in terms of how to implement it sorry - could I not just have a pot at the end of circuit (assuming some sort of buffer /splitter at the start that sends out once audio line to the tremolo and one just dry audio) with dry audio going into lug 1, tremolo audio on lug 3 and then lug 2 to output jack?
I've no idea how to use an octocouple (I don't think I own one anyway) and I have new / different noise issues now - will post them later in the thread
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMA few ideas:
1. You could try to arrange several light sources so they only need one LDR. Use some sort of small light tight container where you have an LDR in one spot. Then arrange all the flickering leds to point the brightest spot of their light towards the LDR.
2. Play around wiht the value of your R2. It should affect the depth of the effect, especially if you put a buffer or another effect in front of the Moidulator. With a passive guitar straight in to the R2 it might not make as big difference.
Thanks! What would be the benefit of only having one LDR? Would that reduce noise then?
I haven't got to R2 yet, but I will try that. I noticed a difference in the audio quality if I plugged the guitar into a boost pedal first, then into the tremolo - there's more of a dynamic range when the tremolo is at fullstrength. I will try to change R2 to see what happens. Would it be better to have a pedal with a buffer in it (like a Boss pedal) to test with or will any boost pedal work (my boost is not a Boss pedal so I have no idea if it has a buffer at all - it's a Caline Orange Burst which is a clone of the Xotic BB Preamp pedal.
Quote from: bluebunny on September 03, 2024, 09:00:00 AM> It's a shame they have to be kept inside a box for the final version; they look like a crazy disco rave migraine inducing light pattern at the moment!
You could have two of each LED: one inside with its respective LDR, and one outside for the light-show! :icon_cool:
Thanks Marc. If I have two LEDs of the same flicker type together they seem to drift out of synch with each other... also I thought they looked dimmer... I think that was when they were in series, maybe it would be different in parallel? I tried that before I rebuilt the circuit and haven't tried again since. They are a bit migraine inducing, so it might be best to stick them inside the box after all!
Quote from: ElectricDruid on September 03, 2024, 10:33:02 AMChase Bliss have recently announced that they're dropping 5 pedals from their range because of vactrol problems. They're selling the remaining stock in the US, where this stuff isn't controlled yet.
I exchanged a few emails with Joel Korte at Chase Bliss, and it seems the catalyst for this is that the *UK* authorities are cracking down on vactrols. Although the UK left the EU (and so the EU's RoHS directive no longer applies in the UK) most EU environmental legislation was rolled-over into UK law on exit so that businesses didn't have a completely-changed legal framework to deal with overnight. He said he's been in contact with several UK pedalmakers who have also had problems.
Whether genuine non-cadmium LDRs are technically possible at some point in the future is a physical chemistry question that I'm not qualified to answer.
This is timely for me since I was about to order more vatrols for the Druid shop, but if the "RoHS" claim on those products is not actually true when independently tested then there's really no point, so I'm holding off until I've found out what the UK's Office of Product Safety and Standards has found out about vactrols.
Thanks for the info Tom. I did some research as well and apparently there are LDRs without cadmium or anything dodgy in them - they are GeCu (Germanium Copper) and they are supposed to be extremely sensitive and cope with huge brightness ranges, so I thought, wow this is just what we need! Then I did some more research. They are infrared only (OK, not the end of the world, infrared LEDs are easy to get), they are designed for astronomers to measure light with and cost around £65 - £175 each!!! Oh, and if that price range wasn't the killer, apparently they really only operate well when chilled to 77 degrees Kelvin... so any pedal using them would need some impressive liquid nitrogen cooling - I bet this is very 'audiophile', but not very practical :)
Quote from: Transistor-Transistor on September 03, 2024, 01:34:03 PMI wonder if there would be a way for phototransistors to act as a replacement for LDR's as they're much easier to find and don't have the Cadmium that Europe doesn't like. I have a 3d printer and I'm planning on making my own vactrols with that (just to be less janky than shrink wrap and duct tape)
Phototransistors and LDR's are not really interchangeable but I'm sure things can be done circuitry wise to make it more similar
Thanks Transistor-Transistor - I also looked into phototransistors but they seem to be for modulating current? Can that be used to modulate resistance? They don't have any banned materials in them which sounds good.
Quote from: PRR on September 04, 2024, 01:13:35 AMIt is going to be digital in the end. Go ahead and develop a GOOD ADC board, compute the optimum gain function, apply it to your bytes. Latency can be 20 MICROseconds which is quite short.
I don't know if my brain is ready for digital yet; I'm still struggling with analogue! As my colleagues who understand coding will tell you - they wouldn't trust me to count from 0 to 1 and get it right; I think digital might be a while (unless it gets a lot easier in future and doesn't require coding)
OK time to bring you uptodate with changes to the circuit. I rebuilt the whole thing on breadboard because it was a mess. It still works (yay!) and each LED has it's own CLR and potentiometer.
(https://i.imgur.com/QVagikL.png)
You'll notice that the first two LEDs have large CLRs, while the other two have small ones (220ohms). There' a sad story about that. I'm not sure if you remember that I said the circuit was rather warm when it only had a 100R resistor in it? And I replaced the 100R with a 470R and that seemed to cool things down? Well I rebuilt the circuit and thought I would try 220ohm resistors on each LED. After a few minutes I thought, that's odd, some parts of the breadboard feel rather warm... and then I stuck my finger on the top of the 78L05. I suspect you're probably all shaking your heads at this point... was it hot? Bloody hell it was hot!
(https://i.imgur.com/ygXT8fw.jpeg)
Anyway after swearing furiously, I unplugged the power, let the 78L05 cool down and swapped it for a larger 7805 which worked fine and didn't get above 45 degrees C. I presume the heat issue was caused by too much current being used by the circuit? And later on, I changed the value of some of the resistors and the heat went away completely, so I was able to swap back to a 78L05.
While testing the circuit I discovered that two of the LEDs (the candle flame ones - D1 and D2) play electronic music when the pots are turned so that the LEDs are at full brightness! Which was cool, but also bloody irritating when you don't want them to sing over the guitar (they are louder than the guitar) and they also sound a bit crap...
If you want to hear them singing, they start to do it at about 1 minute 15 into this recording (I got Moid Junior to play some better guitar for you to hear)
https://drive.google.com/file/d/1hKsF0WjY57h8zJ_EIMMpLsqamwt4s6g1/view?usp=sharing (https://drive.google.com/file/d/1hKsF0WjY57h8zJ_EIMMpLsqamwt4s6g1/view?usp=sharing)
Throughout the above recording I slowly turn all the pots to maximum so you hear stronger tremolo.
To get rid of the techno noises I had to increase the CLR on those two LEDs. The values I used were the smallest I could use that still removed almost all of their audio; the downside is those LEDs are nowhere near as bright now and so do not affect the circuit as well as they did when I used a 220ohm resistor on them. If there is a better way to do this so I can have brighter LEDs please let me know.
I also got my son to play into my caline orange burst pedal (Clean Boost), and then that went into the tremolo, without the techno noise - that sounds like this:
https://drive.google.com/file/d/1zrPVpDEWfrAwSCHqDtIEFaLX0p0ZjYCd/view?usp=sharing (https://drive.google.com/file/d/1zrPVpDEWfrAwSCHqDtIEFaLX0p0ZjYCd/view?usp=sharing)
Throughout the above recording I slowly turn all the pots to maximum so you hear stronger tremolo.
At the moment it seems that unless playing with R2 give a massive change in depth to the tremolo (I will test this), I think I need to buy some more sensitive LDRs, because the tremolo is not as strong as I would like it to be.
Hope you're all having a good weekend
Quote from: moid on September 07, 2024, 06:46:03 PMQuote from: Transistor-Transistor on September 03, 2024, 01:34:03 PMI wonder if there would be a way for phototransistors to act as a replacement for LDR's as they're much easier to find and don't have the Cadmium that Europe doesn't like. I have a 3d printer and I'm planning on making my own vactrols with that (just to be less janky than shrink wrap and duct tape)
Phototransistors and LDR's are not really interchangeable but I'm sure things can be done circuitry wise to make it more similar
Thanks Transistor-Transistor - I also looked into phototransistors but they seem to be for modulating current? Can that be used to modulate resistance? They don't have any banned materials in them which sounds good.
Phototransistors can be used to modulate resistance, and they're very sensitive which you said you wanted. The cons is that they're active components and need to be biased in order to get an output. HOWEVER
They're lower noise :icon_biggrin:
I haven't used them too much but they essentially feel like active LDR's that can do more stuff.
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMA few ideas:
2. Play around wiht the value of your R2. It should affect the depth of the effect, especially if you put a buffer or another effect in front of the Moidulator. With a passive guitar straight in to the R2 it might not make as big difference.
Just tried changing R2 - 100k resistor kills all sound, a 1k makes everything much louder and clearer! Thanks for that, I have changed to 1k. You were right about passive guitar - I couldn't hear much difference between the original 10k and the new 1k, but if I stick a boos pedal in front of the circuit there is a huge volume difference - same thing happens if I use a boost pedal.
Quote from: duck_arse on September 01, 2024, 10:57:39 AMwe are told, when leds cycle, they have "circuitry" inside, and they are inherently noisy. it might be that you can't get them noise free.
sing.
I laughed when I saw your finger. I'm off to listen to Jnr's playing.
Loving Moid Jr.'s playing! Early one the second he slides up before switching to the next chord, great to mix a little lead into the rhythm!
Opto/phototransistos, like LDR but npn's base is light dependant. As Transistor said, very sensitive-but don't flicker.
(https://i.postimg.cc/sv40vG2c/IMG-3656.jpg) (https://postimg.cc/sv40vG2c)
SeePC817 data sheet. (https://www.farnell.com/datasheets/73758.pdf)
Paralleling a resistor with the LDR will lower the value to 1/inverse of sum, I believe. Digi-key's calculator. (https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-parallel-and-series-resistor) So 2 10k resistors give 5k (1/10k+1/10k=2/10k=1/5k). With an LDR having high dark resistance the drop on the other value is small but gives you your new max resistance.
You might ditch the 78L05 and just use 9 volts with big enough CLR. Keep the power decoupling caps though.Looking for flicker LED datasheets it seems 30mA and 2-4volt drop is common-ish. A green led is normally 20mA, 2.1 forward voltage drop.
LEDs use current, so Ohm's Law is your friend there. This calculator (https://www.amplifiedparts.com/tech-articles/led-parallel-series-calculator) is good to see the arrangements either way (parallel/series) with current usage etc and CLR value.
On the volume out thing forget it, just realized your kind of already doing that with LDRs to ground. You could put a small series resistor before them which could make it more pronounced.
Quote from: duck_arse on September 08, 2024, 10:51:48 AMsing.
I laughed when I saw your finger. I'm off to listen to Jnr's playing.
I always knew I had it in me to be an all round family entertainer! I can do witty repartée, cutting one liners
and slapstick. I should get a raise.
Jnr's playing is a lot better than mine - although the few mistakes were due to the room being very dark so that the LDRs wouldn't pick up any stray light, which meant that he couldn't see the fretboard that well.
Quote from: Matthew Sanford on September 08, 2024, 11:53:29 AMLoving Moid Jr.'s playing! Early one the second he slides up before switching to the next chord, great to mix a little lead into the rhythm!
Opto/phototransistos, like LDR but npn's base is light dependant. As Transistor said, very sensitive-but don't flicker.
(https://i.postimg.cc/sv40vG2c/IMG-3656.jpg) (https://postimg.cc/sv40vG2c)
SeePC817 data sheet. (https://www.farnell.com/datasheets/73758.pdf)
Paralleling a resistor with the LDR will lower the value to 1/inverse of sum, I believe. Digi-key's calculator. (https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-parallel-and-series-resistor) So 2 10k resistors give 5k (1/10k+1/10k=2/10k=1/5k). With an LDR having high dark resistance the drop on the other value is small but gives you your new max resistance.
You might ditch the 78L05 and just use 9 volts with big enough CLR. Keep the power decoupling caps though.Looking for flicker LED datasheets it seems 30mA and 2-4volt drop is common-ish. A green led is normally 20mA, 2.1 forward voltage drop.
LEDs use current, so Ohm's Law is your friend there. This calculator (https://www.amplifiedparts.com/tech-articles/led-parallel-series-calculator) is good to see the arrangements either way (parallel/series) with current usage etc and CLR value.
On the volume out thing forget it, just realized your kind of already doing that with LDRs to ground. You could put a small series resistor before them which could make it more pronounced.
Thanks Matthew! Jnr was really happy about your comments :) I honestly don;t know how he does it - he just comes up with things all the time and it's effortless for him. I struggle to remember two chords at a time and a selection of notes that might work with them. And I'm resolved to the fact that my music is more 'abstract' than rhythm based :)
Thanks for the information about phototransistors. As you say - they don't flicker - I had a look at some examples on Mouser, and they seem to be like vactrols (which explains your diagram), so possibly if they were broken apart (split the LED part off) the phototransistor part could be used as an LDR if attached to one of my flickering LEDs? Or they might just break; the packages look very tightly combined and I haven't found a phototransistor separate to an LED yet. They look like they might work as substitutes for LED/LDR combinations that are controlled by a 555 circuit (squarewave or triangle) type LFOs?
I'm going to keep the 78L05 as it seems happy now and everything works around it! What did you mean by "Keep the power decoupling caps though" I didn't have any capacitors in that previous build?
New changes to the circuit. I added a DOD 210 preamp as a booster to the front of the audio. This makes the audio louder (but without adding the fuzz that an LPB1 does) and seems to work with the tremolo happily - sounds similar to the versions I posted previously when I played through a booster pedal first. Does adding this circuit mean I still need a buffer?
(https://i.imgur.com/7pjlQig.png)
The next thing to work on is to try to figure out how to add switches to each LED section so that I can take one or more LED/LDRs out of the circuit when I want to vary which tremolo is functioning. Should the switches be positioned on the little vertical spurs that fall down from the 5 volt power line that goes to each potentiometer, so that each spur can be switched on and off, or should I place the switches on the LDRs somehow to break the connection there? I can't work out what would be best from an audio point of view / least likely to cause issues when I do it.
I definitely need to get more sensitive LDRs as well; even with all the changes the effect of the LEDs is not strong enough - most of the time I hear one LED particularly, and the others kind of blur together. It seems odd to me that I can have 4 of them working on the audio at the same time and still a lot of music carries through - I would've thought there would be moments when 4 LDRs would remove so much audio that it must cut out completely, but I guess that's because they are not sensitive enough.
They have separate phototransistors that look like LEDs like this one. (https://www.digikey.com/en/products/detail/vishay-semiconductor-opto-division/TEPT5700/1681193?utm_adgroup=&utm_source=google&utm_medium=cpc&utm_campaign=Pmax_Shopping_Product_Silicon%20Valley%20Category%20Awareness&utm_term=&utm_content=&utm_id=go_cmp-20773039395_adg-_ad-__dev-m_ext-_prd-1681193_sig-Cj0KCQjwlvW2BhDyARIsADnIe-LZXqcWmDgQoW3381LF6yIB5m3kAeFNjnS4ulx3VjdP9NLygb1LTYAaApmJEALw_wcB&gad_source=1&gbraid=0AAAAADrbLlglUCw9YaAJ9dpB1PSPtqhil&gclid=Cj0KCQjwlvW2BhDyARIsADnIe-LZXqcWmDgQoW3381LF6yIB5m3kAeFNjnS4ulx3VjdP9NLygb1LTYAaApmJEALw_wcB) It seems green is best wavelength to turn it on, but not sure how it'd improve your situation...might be more sensitive.
Put switches before led pots, that way LDRs go max resistance and mess with the others less. You might want to tie the led's pot's pin 3 to 2, they look floating so may catch noise on the breadboard.
Doesn't that FET kind of buffer it too? I'm not sure so asking...
discrete photo transistors - FPT100. also, MEL12 and 2N5777, both photo darlingtons. old parts all, good luck finding.
Quote from: Matthew Sanford on September 08, 2024, 11:40:59 PMThey have separate phototransistors that look like LEDs like this one. (https://www.digikey.com/en/products/detail/vishay-semiconductor-opto-division/TEPT5700/1681193?utm_adgroup=&utm_source=google&utm_medium=cpc&utm_campaign=Pmax_Shopping_Product_Silicon%20Valley%20Category%20Awareness&utm_term=&utm_content=&utm_id=go_cmp-20773039395_adg-_ad-__dev-m_ext-_prd-1681193_sig-Cj0KCQjwlvW2BhDyARIsADnIe-LZXqcWmDgQoW3381LF6yIB5m3kAeFNjnS4ulx3VjdP9NLygb1LTYAaApmJEALw_wcB&gad_source=1&gbraid=0AAAAADrbLlglUCw9YaAJ9dpB1PSPtqhil&gclid=Cj0KCQjwlvW2BhDyARIsADnIe-LZXqcWmDgQoW3381LF6yIB5m3kAeFNjnS4ulx3VjdP9NLygb1LTYAaApmJEALw_wcB) It seems green is best wavelength to turn it on, but not sure how it'd improve your situation...might be more sensitive.
Put switches before led pots, that way LDRs go max resistance and mess with the others less. You might want to tie the led's pot's pin 3 to 2, they look floating so may catch noise on the breadboard.
Doesn't that FET kind of buffer it too? I'm not sure so asking...
Thanks! Switches before pots makes sense now that you explain it. I've made some changes to the circuit (see below) but have only just read your comments. I will tie the floating lugs to pin 2 on hte next iteration.
Interesting thing about the buffer or lack of - with the changes I've made to the power line (see below) the circuit is fairly quiet with a guitar plugged in directly and not playing, but even quieter still when I stick my Boss RC1 in there... so I think the boost circuit works, but a Boss buffer is even better, because without it there is this weird hiss warble sound at around 1.5Khz - when you play it can't be heard, but when you stop playing it is audible on headphones (not sure about speakers; it's late here so I had to turn the amplifier off).
Does this mean I should build a buffer in as well? I wonder if the hiss might be because the new powerline changes affect the tremolo but not the booster circuit. IF I should build a buffer circuit, is there a particular one you would recommend?
If neither Boss pedal or guitar is plugged into the circuit, but the circuit is attached to the amplifier there is quite a loud hum... it disappears as soon as the guitar is plugged in. I'm not worried about that!
Quote from: duck_arse on September 09, 2024, 10:50:34 AMdiscrete photo transistors - FPT100. also, MEL12 and 2N5777, both photo darlingtons. old parts all, good luck finding.
Well I found a chap on ebay who has the FPT100 for sale at a mere £7 each! Couldn't find any MEL12, but 2N5777 are available on ebay for a paltry £14.95! So obviously I ordered his entire stock, I mean for peanuts prices like that I'd be silly not to invest eh? I'll just explain to my family that we don't need to eat this month, but in ten years time we'll be millionaires...
ahem, after a brief consultation with the stakeholders of moid PLC, I think those parts will need to remain in the hands of others for now! Thanks for the suggestion Duck. I'll go back to being a peasant and will make do with what I've got!
Ebay, well, never know what you get! But the link I'd posted for Digi-Key, those were under $1 a piece (US, not sure how they go in UK).
For a buffer, read our wonderful Jack's amazing page about different buffers (https://www.muzique.com/lab/buffers.htm). I'd say scroll past the FET and play with the opamp ones - you'll see a cap either side and a big resistor to bring bias voltage in, make sure you bias it. I think one either end would do you well (after input, before output), you wouldn't need other pedals before but hey it might change it up so keep doing it!
All change ladles and jellyspoons, all change!
(https://i.imgur.com/H1THKQF.png)
Now let it be said that that Electric Druid chap is not just a pretty (or even not just a ruggedly handsome) face; I won't judge... I completely stole the power section from his FilterFX (https://electricdruid.net/filterfx-lp-bp-hp-lfo-filter/) circuit, because Matthew said something about decoupling capacitors and I thought maybe he meant those? Anyway, if you stick that mass of diodes and capacitors into the circuit, guess what? Three of the LEDs stop singing! And I can revert them back to 220ohm resistors for brighter brights and they stay silent :) The fourth LED remained stubborn making a pulsing hiss noise that I hadn't noticed before (but the other noises were louder so it was probably always there)... so I increased its resistor to 1K (I tried every value between 220R and 1K that I had), but even 820R doesn't stop the hiss - however it goes at 1K. The downside is that particular LED is considerably less bright now and doesn't have much brightness range difference between when the pot is full on or full off. So I guess only a more sensitive LDR can save me on that one?
At the moment the new power caps and diode are only affecting the tremolo and not the boost circuit. Should they affect both circuits? In which case I should presumably only use D5, R13, C3 and C4 and conncet them to the 22K resistor on the boost?
Quote from: Matthew Sanford on September 09, 2024, 07:11:00 PMEbay, well, never know what you get! But the link I'd posted for Digi-Key, those were under $1 a piece (US, not sure how they go in UK).
For a buffer, read our wonderful Jack's amazing page about different buffers (https://www.muzique.com/lab/buffers.htm). I'd say scroll past the FET and play with the opamp ones - you'll see a cap either side and a big resistor to bring bias voltage in, make sure you bias it. I think one either end would do you well (after input, before output), you wouldn't need other pedals before but hey it might change it up so keep doing it!
Whoops, I didn't notice the link in your post! Sorry! OK luckily Mouser sell them in the UK and they only cost £0.56 so are perfectly affordable. I might buy a few when I buy the LDRs for future experimentation.
Thanks for the buffer info. If I was to put a buffer before and after, could I use a TL072 so I could use both op-amps in that chip (one for the before buffer and one for the after) or is that considered a bad idea? I can use 2 TL071s if required, but that's a lot of extra space used up if I don't need to! Should the buffer go in front of the boost circuit (I think so?) or between the boost circuit and the tremolo?
Yet another question (what else?) what do you mean by 'Make sure you bias it'? Do you mean try different value resistors there? And what sort of change would I be looking for? EDIT after reading Jack's page again, I think you mean try different resistors between 1M and 10M and see if the audio sounds cleaner / brighter and there isn't any new source of noise.
What I'm about to say may be sacrilege.
You may wanna sit down for this
...
Sometimes if parts are expensive on digikey and mouser you can find them really cheap on Amazon-
(Sometimes I use parts bought from amazon and I haven't noticed a quality difference)
That's my controversy of the day
(Quick edit)
Okay I just looked for phototransistors on amazon and I was way wrong. disregard me
Moreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)
Use a dual, it won't mess with it, so save space!
Digi-key has loads of calculators for most things. If you feel you need a lower voltage you can plug in values to see what you get, has the formulas too.
I hope the actual smart peeps are checking me, don't want to lead you astray.
I knew if I gave you some numbers, you'd find them. you're good like that.
LPT80A Side Viewing Silicon Phototransistor $1.33
LTR-4206 3mm NPN Silicon Phototransistor $1.87
https://au.mouser.com/ProductDetail/Lite-On/LTR-4206E?qs=GHV6gLndNKlNoc%252Btn97dSA==
https://www.digikey.com.au/en/products/detail/liteon/LTR-4206E/121710
SFH325G Side LED SMD NPN Sensor Phototransistor $0.61
https://au.mouser.com/c/?q=SFH325
I found three obsolete parts at my nearest surplus joint, Rockby. plenty cheep options at digikey and mouser. dunno why you want them, tho.
Quote from: Transistor-Transistor on September 09, 2024, 08:15:37 PMWhat I'm about to say may be sacrilege.
You may wanna sit down for this
...
Sometimes if parts are expensive on digikey and mouser you can find them really cheap on Amazon-
(Sometimes I use parts bought from amazon and I haven't noticed a quality difference)
That's my controversy of the day
(Quick edit)
Okay I just looked for phototransistors on amazon and I was way wrong. disregard me
No need to apologise, I'm happy for any tips - so thanks for saying so. I've usually found Amazon to be more expensive unless I'm buying one of those bundled kits of components (or I run out of a certain part and it will take a few days for something to arrive from an electronics specialist and I really want it now, so I just buy a lot of one part and I know it will arrive the next day... don't ask me how I've got too many resistors of very obscure values that I doubt I will ever use in this lifetime!
Quote from: Matthew Sanford on September 09, 2024, 08:16:52 PMMoreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)
Use a dual, it won't mess with it, so save space!
Digi-key has loads of calculators for most things. If you feel you need a lower voltage you can plug in values to see what you get, has the formulas too.
I hope the actual smart peeps are checking me, don't want to lead you astray.
Thanks Matthew. I'm going to have to draw this out in schematic first before I start ripping the breadboard apart to get the buffer in (I've run out of space on that breadboard)... Hmmm I wonder if you can get bigger breadboard; I bet it's possible... I'm going to look :)
Post your drawings! Good for a spot check...
And bigger! I'd bought those six pack of littles, they all have stuff living on them now so had to get a big board, like 4 tall stuck together...which now has stuff living on it too
Quote from: duck_arse on September 10, 2024, 11:44:23 AMI knew if I gave you some numbers, you'd find them. you're good like that.
LPT80A Side Viewing Silicon Phototransistor $1.33
LTR-4206 3mm NPN Silicon Phototransistor $1.87
https://au.mouser.com/ProductDetail/Lite-On/LTR-4206E?qs=GHV6gLndNKlNoc%252Btn97dSA==
https://www.digikey.com.au/en/products/detail/liteon/LTR-4206E/121710
SFH325G Side LED SMD NPN Sensor Phototransistor $0.61
https://au.mouser.com/c/?q=SFH325
I found three obsolete parts at my nearest surplus joint, Rockby. plenty cheep options at digikey and mouser. dunno why you want them, tho.
Thanks Duck. The UK doesn't seem to have cheap surplus electronic component stores at all. I've searched and there are plenty of surplus stores, but they all seem to be of the 'we know what we've got, no low ball offers' and the prices are quite silly... Maybe surplus stores are more of an Australian / North American thing? Or if they are actually cheap, you have to buy the components in huge quantity... I saw one had CD4046 and CD4049 ICs for really cheap... but you had to buy 50 - 100 minimum order.
Thanks for the mouser tips though!
I did some checking on the mouser phototransistors and they are all aimed at the infrared end of the spectrum so I don't think they'll work with the coloured LEDs I'm using. I did find TEPT5700 which are aimed at human visible light, so I'll buy a few of those in case they come in handy, but I'm hoping to use one of the other LDR types I'm ordering.
The IR peak is intrinsic in Silicon photosensors. Digital cameras mostly need IR filters so we don't see "ghosts". (Or they use IR response to face-check in near dark.)
LEDs are BRIGHT. You do not have to worry about color preference in most cases. I drove lots of "green peak" LDRs with red LEDs. Often the problem is "too much" response.
We were trying to build a touch panel for avionics use a few years (decades?) back and we decided that there was no way to filter out bright sunlight at high altitudes with IR sources, but we used green LED's with other green LED's as photosensors. LED's will work as photosensors, but they have a high leakage current and this leakage has a strong temperature coefficient (higher temp = more leakage) and the leakage current is on a par with the signal current (sort of like germanium). We couldn't make it work for our purposes, but it is another possibility to consider.
I kind of dropped out of this conversation for a while and I'm not sure if someone else answered or you gathered the info somewhere somehow, but anyway... I'll continue with in some things I started with.
Quote from: moid on September 07, 2024, 06:46:03 PMQuote from: Elektrojänis on September 03, 2024, 05:37:25 AMA few ideas:
1. You could try to arrange several light sources so they only need one LDR. Use some sort of small light tight container where you have an LDR in one spot. Then arrange all the flickering leds to point the brightest spot of their light towards the LDR.
Thanks! What would be the benefit of only having one LDR? Would that reduce noise then?
Benefit of one LDR only would mainly be saving parts. The result will quite possibly be very similar if yo can arrange the leds pointing to the single ldr. Maybe you could use some sor of small container for them and hot glue the parts in. I'd probably use an old black 35 mm film canister but I quess the availability of those is not as good as it used to be... And some are translucent instead of black, which does not help with stray light at all.
Quote from: moid on September 08, 2024, 07:01:38 AMQuote from: Elektrojänis on September 03, 2024, 05:37:25 AM2. Play around wiht the value of your R2. It should affect the depth of the effect, especially if you put a buffer or another effect in front of the Moidulator. With a passive guitar straight in to the R2 it might not make as big difference.
Just tried changing R2 - 100k resistor kills all sound, a 1k makes everything much louder and clearer! Thanks for that, I have changed to 1k. You were right about passive guitar - I couldn't hear much difference between the original 10k and the new 1k, but if I stick a boos pedal in front of the circuit there is a huge volume difference - same thing happens if I use a boost pedal.
The thing with those LDR's and the R2 is that they act as a voltage divider. It's much like a volume pot. Maybe a simplified picture will help. I this doesn't go too simple.
(https://i.postimg.cc/fk7Cv4N8/divider.png) (https://postimg.cc/fk7Cv4N8)
Volume pot arranged like on the left is probably familliar to you. It works like the thing I drew on the right. The two resistors added is the total value of the volume pot and turning the pot makse one of the resistors smaller and the other bigger.
If you strip down the signal side of the Moidulator to bare minimum with only one LDR, you also get the circuit on the left side (I even wrote R2 and LDR there). The output signal will be the (LDR/(LDR+R2))*input.
When the Moidulator is working, the LDR is changing acording to the light from the LEDs. R2 is not changing. If R2 is too small compared to the range of resistances of the LDR (from dark to light) the signal throigh will be loud, but not changing much. If the R2 is too big the signal through will be too quiet (and not changing that much).
The key to maximizing the modulation depth, is to find a value for R2 that is similar to the average resistance of the LDR for the operating conditions (light brightness) you put it in. Or somewhere in that ballpark anyway. If it get's too quiet, you need a booster... You have that booster there now already, and it is really needed, as the core element can only make things quiter.
Oh... Back to circuit with 4 LDR's. The rest of those are parallel to the first one so you might need slightly lower R2 with all four of them. Only slightly smaller. Like if the optimum was x ohms with one, then the optimum with 4 LDR's is x/4 ohms at the very minimum. As the all LDR's are modulated differently, x/2 is likely closer to optimum, but it really depends on the modulation your flickering leds provide.
I hope that makes sense to you and maybe helps a bit.
Edit: Oh... If there is no buffer at the input, the guitar pickup itself is in series with R2. You can consider it as a part of R2 on my simplification. The pickups usually have a resistance from a few kilo ohms to maybe 20 kohms, but that's at DC (0 Hz). At audio frequencies the impedance (resistance when it is not same for all frequencies) is much higher. That's why changing the R2 without a buffer/booster didn't change much, but with buffer/booster the change was more noticeable.
Quote from: PRR on September 11, 2024, 07:31:39 PMThe IR peak is intrinsic in Silicon photosensors. Digital cameras mostly need IR filters so we don't see "ghosts". (Or they use IR response to face-check in near dark.)
LEDs are BRIGHT. You do not have to worry about color preference in most cases. I drove lots of "green peak" LDRs with red LEDs. Often the problem is "too much" response.
aah... well I already ordered the parts, now I have to wait... I will rememberthat for next time though. I just lookd at the diagram in the datasheet that showed responsiveness to light and assumed I should always look at the brightest as being the best... it never occurred to me that too bright was an option! I've ordered a bunch of LDRs so hopefully the circuit can be made into something good with those and I won't have to look into how to add phototransistors (I did buy some of those) because I have no idea how to integrate those into the circuit. Fingers crossed the LDRs are what I need! I also ordered some larger breadboard because the circuit is too big as it is to add more parts.
Quote from: amptramp on September 12, 2024, 11:14:18 AMWe were trying to build a touch panel for avionics use a few years (decades?) back and we decided that there was no way to filter out bright sunlight at high altitudes with IR sources, but we used green LED's with other green LED's as photosensors. LED's will work as photosensors, but they have a high leakage current and this leakage has a strong temperature coefficient (higher temp = more leakage) and the leakage current is on a par with the signal current (sort of like germanium). We couldn't make it work for our purposes, but it is another possibility to consider.
That's interesting amptramp - could you not use UV filters like you get for camera lenses, or are they not strong enough at high altitude? I remember being taught to use a UV filter as a standard precaution on any lens in case you dropped it (this was at art college; they were probably tring to stop us students from breaking expensive lenses!)... and it was just a good idea when shooting colour slide film of daylit landscapes anyway (removed a slight purple tint from the film). I wonder what digital cameras on phones do? Presumably they have some kind of built in filter on the lens?
Quote from: Elektrojänis on September 14, 2024, 01:21:37 PMI kind of dropped out of this conversation for a while and I'm not sure if someone else answered or you gathered the info somewhere somehow, but anyway... I'll continue with in some things I started with.
Thanks very much!
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMBenefit of one LDR only would mainly be saving parts. The result will quite possibly be very similar if yo can arrange the leds pointing to the single ldr. Maybe you could use some sor of small container for them and hot glue the parts in. I'd probably use an old black 35 mm film canister but I quess the availability of those is not as good as it used to be... And some are translucent instead of black, which does not help with stray light at all.
I have seen something similar inside my Moen Shakey Jimi vibrato pedal - that has two LDRs both aimed at an LED (I think, it has been a while since I opened it). In the original pedal the LDRs are a certain distance from the LED, and an easy mod to make a stronger effect was just to bend them closer to the LED and angle them at it! In the original they point upwards, parallel with the LED! So tilting them by 90 degrees and putting them closer gives a much stronger vibrato effect. Probably the easiest mod I've ever done :)
Anyway, yours is an interesting idea - for now I will try the multiple LDRs because I'm wondering if the different LEDs I am using would each benefit from an LDR with different characteristics - maybe, maybe not, but seeing as I've ordered some different ones I am going to find out!
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMThe thing with those LDR's and the R2 is that they act as a voltage divider. It's much like a volume pot. Maybe a simplified picture will help. I this doesn't go too simple.
I'm not sure if it is possible to go to simple for me! I have a tenuous grasp of electrical theory at the best of times, and when I do make / change things it's kind of like watching an orang utan that has been given some tools to play with... I know these things in front of me do stuff, but the order you have to put them together can be challenging :) and the outcome may be wild and experimental with more passion than understanding!
(https://media1.tenor.com/m/IvnEllOXaSkAAAAC/orangutan-monkey.gif)
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AM(https://i.postimg.cc/fk7Cv4N8/divider.png) (https://postimg.cc/fk7Cv4N8)
Volume pot arranged like on the left is probably familliar to you. It works like the thing I drew on the right. The two resistors added is the total value of the volume pot and turning the pot makse one of the resistors smaller and the other bigger.
If you strip down the signal side of the Moidulator to bare minimum with only one LDR, you also get the circuit on the left side (I even wrote R2 and LDR there). The output signal will be the (LDR/(LDR+R2))*input.
When the Moidulator is working, the LDR is changing acording to the light from the LEDs. R2 is not changing. If R2 is too small compared to the range of resistances of the LDR (from dark to light) the signal throigh will be loud, but not changing much. If the R2 is too big the signal through will be too quiet (and not changing that much).
The key to maximizing the modulation depth, is to find a value for R2 that is similar to the average resistance of the LDR for the operating conditions (light brightness) you put it in. Or somewhere in that ballpark anyway. If it get's too quiet, you need a booster... You have that booster there now already, and it is really needed, as the core element can only make things quiter.
Wow, thanks that's brilliant - so that's why I need R2 in the first place, and also why I shouldn't just leave it out! So this means if I change the LDRs I may need to change R2 to compensate. This also explains why I thought the 'off' part of the tremolo was a bit deeper when I was using 10K for R2; however the overall volume of the circuit was much quieter. A switch to 1K made the circuit a lot louder (with a boost and / or a Boss buffer) but I thought the quieter parts were not as quiet as they were before. OK I will keep that in mind when the new parts arrive, and will try them and also adjust R2 if I don't get the volume where I want it to be.
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMOh... Back to circuit with 4 LDR's. The rest of those are parallel to the first one so you might need slightly lower R2 with all four of them. Only slightly smaller. Like if the optimum was x ohms with one, then the optimum with 4 LDR's is x/4 ohms at the very minimum. As the all LDR's are modulated differently, x/2 is likely closer to optimum, but it really depends on the modulation your flickering leds provide.
I hope that makes sense to you and maybe helps a bit.
It does thanks - I will bear this in mind when 'tuning' the circuit!
Quote from: Elektrojänis on September 03, 2024, 05:37:25 AMEdit: Oh... If there is no buffer at the input, the guitar pickup itself is in series with R2. You can consider it as a part of R2 on my simplification. The pickups usually have a resistance from a few kilo ohms to maybe 20 kohms, but that's at DC (0 Hz). At audio frequencies the impedance (resistance when it is not same for all frequencies) is much higher. That's why changing the R2 without a buffer/booster didn't change much, but with buffer/booster the change was more noticeable.
Aahh so the buffer acts as... well, a buffer! (now I know how it got its name!) it sits between the pickup and the circuit so the pickup doesn't become part of the equation for the voltage divider. Thanks again, I've learned a lot from this post.
To piggyback on Electrojänis, for R2, you might try a trim pot with a high value with pin 2 connected to pin 3 - makes it a variable resistor, turning CW reduces it. Once it's what you want, check between pin 1 and 2 and that should be your R2 value
Quote from: Matthew Sanford on September 14, 2024, 08:36:20 PMTo piggyback on Electrojänis, for R2, you might try a trim pot with a high value with pin 2 connected to pin 3 - makes it a variable resistor, turning CW reduces it. Once it's what you want, check between pin 1 and 2 and that should be your R2 value
to piggybank on Sanford/Janis, if you made R2 one of the ldr's, you could add some random depth. but it will still be noisy if lit by a candle.
my camera teacher said always have a daylight on all your lenses, because replacing a filter covered in dirt and smudges and grime is cheaper than replacing a fingerprinted lens. I used rubber hoods/shades, and tried not to drop lenses.
Surprise everyone! I finally got a couple of hours away from work to redraw the schematic with a buffer in front and after the circuit.
Quote from: Matthew Sanford on September 09, 2024, 08:16:52 PMMoreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)
Use a dual, it won't mess with it, so save space!
(https://i.imgur.com/yvkHAEE.png)
Sorry this is rather cramped (and probably confusing). I am fairly sure I got the input buffer part right according to Matthew's instructions, however I'm not sure if I got the output buffer part correct... I couldn't decide if the output buffer of the TL072 required the same voltage dividor components or whether I could take a cable from the input buffer components to pin 5 of the TL072 or not... in the end I added the same components to both the input and output buffers so please let me know if I just unnecessarily doubled up the components!
Another thought - should the power to the TL072 and the DOD 210 part of the circuit come after the 1N5187 diode that is part of the power supply for the LEDs?
If you think the above circuit would work I will start ripping the breadboard mess apart and test it (it might be a few weeks before this happens, work is going to be relentless until near the end of November :( ) so dont be holding your breath...
Hope you're all having a great weekend!
Quote from: Matthew Sanford on September 14, 2024, 08:36:20 PMTo piggyback on Electrojänis, for R2, you might try a trim pot with a high value with pin 2 connected to pin 3 - makes it a variable resistor, turning CW reduces it. Once it's what you want, check between pin 1 and 2 and that should be your R2 value
That's a good idea! Thanks very much, OK I'll try that once I get to breadboarding the new schematic.
Quote from: duck_arse on September 15, 2024, 10:52:30 AMQuote from: Matthew Sanford on September 14, 2024, 08:36:20 PMTo piggyback on Electrojänis, for R2, you might try a trim pot with a high value with pin 2 connected to pin 3 - makes it a variable resistor, turning CW reduces it. Once it's what you want, check between pin 1 and 2 and that should be your R2 value
to piggybank on Sanford/Janis, if you made R2 one of the ldr's, you could add some random depth. but it will still be noisy if lit by a candle.
my camera teacher said always have a daylight on all your lenses, because replacing a filter covered in dirt and smudges and grime is cheaper than replacing a fingerprinted lens. I used rubber hoods/shades, and tried not to drop lenses.
Random depth is a cool idea - but I expect you mean an LDR on the outside of the enclosure? I suspect that could be highly irritating to control (a friend of mine once lent me a weird DIY fuzz pedal he had bought from ebay that had an LDR on the enclosure to add oscillating noise in some way - which it did (I think it was supposed to modulate the gain somehow), but it always made annoying noises unless the level of illumination hitting it was just right. He said it was cool on stage with flashing lights, but it was next to useless at home if daylight came through a window. This was before I got into building pedals so I never took any photos of the insides and he got sick of it and sold it, so I've no idea what it was... only that I don't think I'd want an LDR on the outside of the box!
Yes our teacher showed us in a catalogue how much we would have to repay if we broke a lens versus how cheap a UV filter was to replace... so I remembered that lesson (also I try not to drop lenses, and I've so far been good at that!)
Quote from: moid on September 28, 2024, 04:09:15 PMRandom depth is a cool idea - but I expect you mean an LDR on the outside of the enclosure? I suspect that could be highly irritating to control (a friend of mine once lent me a weird DIY fuzz pedal he had bought from ebay that had an LDR on the enclosure to add oscillating noise in some way - which it did (I think it was supposed to modulate the gain somehow), but it always made annoying noises unless the level of illumination hitting it was just right. He said it was cool on stage with flashing lights, but it was next to useless at home if daylight came through a window. This was before I got into building pedals so I never took any photos of the insides and he got sick of it and sold it, so I've no idea what it was... only that I don't think I'd want an LDR on the outside of the box!
Yes our teacher showed us in a catalogue how much we would have to repay if we broke a lens versus how cheap a UV filter was to replace... so I remembered that lesson (also I try not to drop lenses, and I've so far been good at that!)
There is one reason to put a photoresistor on the outside of the box - to control the indicator LED current. This allows you to use a high-brightness LED in full daylight or a dark club ambient and allows you to see the light under both conditions without being blinded. You may need parallel and series resistors to "tune" the brightness response.
Quote from: moid on September 28, 2024, 03:57:35 PMSurprise everyone! I finally got a couple of hours away from work to redraw the schematic with a buffer in front and after the circuit.
Quote from: Matthew Sanford on September 09, 2024, 08:16:52 PMMoreover just make sure a midpoint voltage (4.5 for 9 Vcc) is present on the + in. I don't think resistor values matter much if you set it like Jack's example, however... I like to set up the divider with a couple 10ks, one to V+, one to ground, then where they meet (giving 4.5 volts as half the power supply) use a 1 Meg resistor to bring it to the op amp. You should also put a cap, say 10uF from that midpoint to ground to keep it stable-don't use the cap if it's going to an LFO generator (thanks to Duck for that). Reason for lower bias divider resistors and big ones to bring it in is that big one essentially is parallel to the one going to ground, so making it decades larger doesn't change the divider resistor value (much...)
Use a dual, it won't mess with it, so save space!
(https://i.imgur.com/yvkHAEE.png)
Sorry this is rather cramped (and probably confusing). I am fairly sure I got the input buffer part right according to Matthew's instructions, however I'm not sure if I got the output buffer part correct... I couldn't decide if the output buffer of the TL072 required the same voltage dividor components or whether I could take a cable from the input buffer components to pin 5 of the TL072 or not... in the end I added the same components to both the input and output buffers so please let me know if I just unnecessarily doubled up the components!
Another thought - should the power to the TL072 and the DOD 210 part of the circuit come after the 1N5187 diode that is part of the power supply for the LEDs?
If you think the above circuit would work I will start ripping the breadboard mess apart and test it (it might be a few weeks before this happens, work is going to be relentless until near the end of November :( ) so dont be holding your breath...
Hope you're all having a great weekend!
It looks pretty good. On the bias, take the 10ks divider off your input line. Have the divider set up, then use the 1M resistor from the midpoint of the 10ks to the non-inverting input. The signal doesn't need to go through it, it needs to bring that voltage to the signal line. You can use one 10k divider, and one 1M resistor to take it to each input. Also good to have a 10u capacitor from divider midpoint to ground.
Some examples cut from others
(https://i.postimg.cc/cgVbmwyZ/IMG-3703.jpg) (https://postimg.cc/cgVbmwyZ)
(https://i.postimg.cc/wRLbbMgN/IMG-3704.jpg) (https://postimg.cc/wRLbbMgN)