Blinking LEDs out of phase

[moosapotamus]

R.G. - That's pretty cool! Thanks for sharing.

Could you get it to work like an envelope follower if you fed it with a guitar signal (w/ added gain, maybe?) instead of an LFO?

~ Charlie

[R.G.]

Hmm. Interesting question.

I think it doesn't work well with an AC guitar signal, but feeding it an envelope would work.

As shown, the LEDs naturally sit at half-brightness (well, OK, half current) with an input at the Vref (or adjusted to look that way by the trimmer). An AC signal like guitar would make the LEDs track out of phase up and down, OK, but the receiver, often a human eye or an LDR, would average this so that they still looked like they were at half-brightness all the time, in spite of them running back and forth madly. They're still doing the right thing, but a human eye or an LDR couldn't tell it. That's why doing an envelope ahead of it would work better.

If you had an envelope that was at ground for silence and a volt or two for signal peaks, you could sure make the thing have one LED off and one fully on with silence, and these would flip states on the peak of the envelope, then slide back to the silence value.

[samhay]

moosapotamus - if you want an envelope detector, the first schematic I posted (essentially the compressor without the LDR: http://www.diystompboxes.com/smfforum/index.php?topic=101118.0) is probably a better bet. Collectively, the 2 LEDs give you a full-wave rectification of the signal, and the relatively slow response of the LEDs/LDR (if using one) will smooth it out to give you something like a classic envelope detector.
The schematics that Rob and R.G. posted are great with really slow LFOs (few Hz), but much faster signal will smear out the LEDs response and the extra engineering required will be largely unnecessary.

[moosapotamus]

...feeding it an envelope would work.

Cool! Two envelope detectors that simultaneously sweep in opposite directions (hmmm...)? I might have to find some time to give that a try.

Thanks
~ Charlie

[samhay]

While this has been a fun intellectual exercise, I have been struggling to find a good use for the out-of-phase LEDs.
As a warm up, I cobbled together a 2 stage phaser/vibe on the breadboard that is similar to one of the links that Jimi posted earlier (http://sound.westhost.com/project49.htm; very similar to the MadBean smoothie and its brethren). I am currently using 2 LEDs in phase to drive a couple of LDRs in place of the FETs. The LDRs are not especially matched yet it works really well - it sounds very watery and I quite like it. Using the square wave out of the LFO is surprisingly useful too - I guess the slow response of LEDs/LDRs has there advantages.
I am now trying to work whether there is any milage in further molesting it with another set of LEDs/LDRs out of phase. Jimi - what did you have in mind initially.

[pinkjimiphoton]

hi sam,
originally i wanted to kinda ape that phasey kind of tremolo on the old blonde fenders.
i still haven't had a chance to revisit this yet, trying to get a bunch of business taken care of.
would LOVE to see a layout of what ya did, seems like you're on the path!
the idea was to use a lp and hp filter... one on each of the blinky pairs.. so that when say treble is being tremoloed, the bass isn't.. each pulse it will switch.
does that make any sense?
at high speeds i'm imagining it'll sound a little metalic, at low speeds i'm hoping to get that wobble kind of sound.
with your experimenting, do you think it's feasible?
i looked at RG's ersatz fender vibe etc, but i wanna do something veroboard friendly. that's just a wee bit over the top for me still i think.

[moosapotamus]

That's a cool idea, Jimi. I was thinking of a filter application, too... like replacing the LED envelope follower in something like the Anderton Bi-Filter Follower so that the two filters would simultaneously sweep in opposite directions. I have no idea if it would sound any good, but it seemed like another cool idea.

~ Charlie

[electrosonic]

originally i wanted to kinda ape that phasey kind of tremolo on the old blonde fenders.

What about this...

Take the BMP tone stack, replace the pot with two LDRs in series the output is taken from the junction of the LDRs. Make an LFO with two outputs out of phase and drive the LDRs with that.

Andrew.

[samhay]

I was initially thinking about a tremolo that alternatively and/or simultaneously swept a LP and HF filter. I don't know why I haven't tried that yet. I freed up some breadboard space last night so will move that the the front of the queue.
Jimi, I'm guessing that you are still looking for the old Fender 'harmonic vibrato' sound. Something link this: https://www.youtube.com/watch?v=7dChBeEYIkM?  I think we can get close with an optical phaser/vibe that I would imagine will fit in a 1590B on vero. I will post a preliminary schematic (there is nothing that hasn't been done before though) and sound clips as soon as I can cobble them together.

[deadastronaut]

interesting ideas guys...

[samhay]

Here's what I have thus far. It is a work in progress, and not very original. With the square wave LFO and vibe switch open you get a pretty nice tremolo. The two fixed all-pass filters fatten up the phaser sound a fair bit, but are very much an optional extra.

[pinkjimiphoton]

god, have i told you guys how much i love you lately?


cuz i DO!! (umm, platonically...don't get too excited there, mungo straight)

sam,  the harmonic vibratto is exactly what i was hoping to lummox across in a simplified "sound alike" kinda form.
perfect.

charlie, i had the exact same idea the other nite!! either we both got great minds, or you got as much pus betwixt the ears as me!!


sam, i'm gonna try your circuit out asap..

i gotta tcob a little, so bear with me!! thanks bro!

[samhay]

Jimi - you might want to look at the Hollis EasyVibe http://www.hollis.co.uk/john/circuits.html. I had forgotten about this, but it is very similar to what I posted - it uses 4 LED/LDR combos and the LFO is a bit more magnificent - and it might well do the trick. There are a bunch of layouts for it kicking around and you shouldn't have too much trouble finding sound clips on youtube etc.

[pinkjimiphoton]

but... i wanna see THIS thing in action.

i've seen the easyvibe, i don't need a vibe so much as a tremolo that "sounds like" the fender harmonic vibrato.

so.. see if i got this right... two dual opamps and a quad?
any pref for which opamps to use where?

i've got the usual tl06/7/82's, 4558's etc .

lm324's etc for the quad.

thanks sam, this looks easy enough even i hopefully can't bugger it too badly.

[samhay]

OK fair enough.
Had more of  a play last night. For a tremolo sound, you can probably drop the 2 optional stages. Not sure how much use the vibe/phaser switch is either. The mojo seems to be in the square/triangle switch. I am using TL072/4s on the breadboard. There is a little bit of ticking that is probably coming from the LEDs. Using a TL062 (I'm out of these at the moment) for the LFO and whatever else you want for the audio would be worth a shot. I like TL072s for the input buffer so you have more input impedance than you can shake a stick it.
My LDRs get down to ~10k when lit together with 1 LED driven from the LFO, so this seems to be workable. If you want/need a deeper effect, use 2 x 1LED/1LDR combos.

Edit: You might need to add a BJT buffer between the LFO and the LEDs like in Rob's suggestion. Also, you can bump up the 56k feedback resistor in the LFO to 82k (or use a trimmer) to get a bit more voltage swing.

[electrosonic]

Here is an old circuit from the internet's past - I have used it for LED eyes at Halloween (similar to posted except LEDs are buffered). (It needs a rate pot - the 47k resistor can be replaced by a pot + resistor)



Credit: image taken from here - http://www.bowdenshobbycircuits.info/fade_led.htm

Andrew.

[samhay]

Thanks Andrew - looks like the same idea as Rob posted.

Seeing as we are back on topic - I found some 2 leg bi-colour (red/green) LEDs in my stash today. If I understand correctly, these are just anti-parallel LEDs in a single package; reverse the polarity and you change the colour. I think that you could put one of these in the feedback loop of the schematic I originally posted to smoothly alternate between red and green via orange. I have seen LDRs with both 530 nm (green) and 600 nm (red) peak sensitivities. These are pretty broad (100+ nm FWHM) peaks, but you might be able to get a useful response out of a 1 bi-colour LED/2 LDR combo...

Edit: works with a square wave - alternates between red and green at low speed then eventually get an orange blur at faster rates. With a triangle wave, you just get orange.

[PRR]

> rate pot - the 47k resistor can be replaced by a pot + resistor

FWIW: the 47K+100K at pin 5 control the output level as well as the rate. As a blinker, no big deal until you get to tiny values.

But if you like the Triangle output: The 100K to pin _2_ only controls rate. Using LM324, values from 2K to 1meg should work and cover over 8 octaves of rate. If it still won't go where you need, change the 22uFd+22uFd to perhaps 0.1uFd for audio, 470uFd N.P. for glacial.

[samhay]

> rate pot - the 47k resistor can be replaced by a pot + resistor

FWIW: the 47K+100K at pin 5 control the output level as well as the rate. As a blinker, no big deal until you get to tiny values.

But if you like the Triangle output: The 100K to pin _2_ only controls rate. Using LM324, values from 2K to 1meg should work and cover over 8 octaves of rate. If it still won't go where you need, change the 22uFd+22uFd to perhaps 0.1uFd for audio, 470uFd N.P. for glacial.

Yup - that's exactly what I would recommend too, and this is almost (I used a 10k limiting resitor) exactly how the LFO in the above phaser schematic is laid out.

[samhay]

In a vain attempt to make use of the alternating LEDs, I put together a 4 stage phaser on the breadboard where the first 2 stages swept up and the other two down. I guessed there is a reason why that design hasn't taken off and I was mostly right. It makes for an interesting effect - quite tremolo like - but not as nice as the straight phaser sound you get with 4 stages sweeping in the same direction and not likely to be worth the engineering effort.

I have had to play with the power filtering quite a bit - starting to appreciate why the EasyVibe has such a weird Vref - and it is now quite acceptable for the triangle wave. It ticks quite badly with the square wave output and I am pretty sure this is because the Vb power rail is spiking everytime the LDRs start swing down. Buffering it is not quite cutting it, so I am not sure that I want to go much futher down the square wave implementation.
I think I am just about ready to put this to bed, but might box up a simple little optical phaser before I clear the breadboard. I see that Jon (midwayfair) has just posted an optical implementation of the Harmonic Tremolo, which should keep Jimi happy for a while.