astable circuit "squeal" issue

[GibsonGM]

One side of that one chip isn't working, you mean?  Or that you just have no luck using it like 2 555's, and always have this problem any time you use a 556?

If the first, the chip might be damaged...is it a CMOS type?  (read off the part number on it).

If the second, does it do anything at ALL?   Lessee, things to know: 556 has a different pinout than the 555, so you'd need to look it up if you don't have it.  If you know that, sorry, had to mention it

Have you tried the 'stabilization caps' we talked about above?  Still need 'em with the 556.

Best way to approach this is probably for you to post the schematic you're working from...build it on breadboard, double=triple check every single thing, then report in what the bugs are!    Get us all on the same page so we're not just talking 'in general'...   

Here is one guy's take on it, might be helpful. http://makezine.com/2011/09/13/collins-lab-atari-punk-console/

[bluzeyonecat]

First off, thank you for all your help. The decoupling worked very well on a 555 build. I tried using the 100R going from positive to pin 8 and I couldn't get any sound on a 5V circuit. However When I placed The 100R with the 1000uf cap further down the breadboard and used a regular jumper from positive to pin 8 it worked fine. Is that correct? Or is ears playing tricks?

[bluzeyonecat]

Tomorrow I have a day off from gigs and set list preparations so I plan on running various experiments. Wiring up the 556 will be one of them. If it still doesn't work, I'll explain my work with as much detail as I can. Maybe even pics. What is the procedure for uploading photos here? Thanks for your time.

[bluzeyonecat]

One thing I'm finding out quick about this electronics gig is its alot like music. One answer leads to another question. Between that similarity and the fact that the motion of waves are intangible, I think its that mystique that I dig about it.
That said, heres another question. Above, concerning protecting your pot, Mr. Gibson mentioned adding a 390 R in series with it. I understand the implication, but not so much the process.
If I tie, say leads 1 & 2 together and apply that to the desired variable situation in a circuit, and bring lead 3 to ground, where do I utilize the 390R? Or were you suggesting that if I was bringing lead 1 from the voltage supply and use lead 2 independently?
I certainly want to put your method into practice as I've already roached a few pots (some costly. Thank you so much for all your help.

[antonis]

I think that Mr. Gibson (or may I call him Sir..??) made himself clear enough when he wrote IN SERIES with the pot ...
(He definately is a very harsh and retisent person who doesn't like to be misunderstood...)

It doesn't matter if you place the resistor between lug 3 and GND or between lug 1 and 9V...)

[GibsonGM]

Hi Bluze...Don't listen to Antonis (ha ha) - I often own up to the holes in my own knowledge, being self-taught and all - I often make mistakes...there are many real-world engineers in here who took real-world classes, and so can have a much better understanding of the major principles behind anything I might say!  I can't recall if I've been harsh to anyone who asked a question - I hope not!! 

The 100R resistor and cap to ground is more for problems with low frequency oscillators making 'ticking' noises, as you may find in a tremolo. Won't do much for squeal, I think.   The bypass caps going from power to ground, right at the chip (across the pins) that we talked about might, and have the best chance for success.   The 100R trick is just a big filter with a big reservoir.

What antonis said - if you want to play with a pot and voltage, you need to think about what happens at that particular voltage.  Parts have a power rating, which is obtained by (among other version of the formula) voltage * current.    So we do 2 steps, which I laid out earlier - Ohm's law to find current at near-minimum for the pot (maybe 100 ohms?), and then plug that into Watt's law, voltage * current.
We find that for a 1/4W rated pot (most for stomps are), we'll go well over that even at 9V if we turn the pot down too far!   Then it burns up and is useless (usually).  Certainly gets damaged and is then unreliable. 

So we put a "LIMITING RESISTOR" in series with the pot in cases like this (where there is nothing else limiting the power).  Like Antonis said, doesn't matter where in the 'chain' it goes...on the + in side, or the - out side, either is fine.     I calculated that to be about 390 ohms for safety, as 9/390=.023A   and 9*.023=.20W, under our .25W rating.   In addition, most LEDs you might mess with using the pot will be safe from too much current - the 390 acts as their limiting resistor, too!   You then can't draw any more than the ~20mA that the limiting resistor allows; you can only go down from there.  The circuit is safe, even if you turn your pot to zero.

It took me a long time as a noob to really understand that in cases like this...turning the pot DOWN mean I was making it dissipate MORE current - it can seem intuitively that turning it down should make things "safer", but it's the opposite, ha ha....that flowing current has to go somewhere, so you're putting the brakes on it, and making power dissipate as heat in the pot....or hopefully in that limiting resistor instead. 

[duck_arse]

I think that Mr. Gibson (or may I call him Sir..??) made himself clear enough when he wrote IN SERIES with the pot ...
(He definately is a very harsh and retisent person who doesn't like to be misunderstood...)

.... it's all that blue blood of his, antonis.

and while you have the 100R in the supply line and non-functioning 556/555 circuit bluezey, measure the voltage across that resistor. it may prove instructive.

[GibsonGM]

My blood surely feels blue today, Duck, given the flu and everything!!!   

I checked out (LT Spice) adding a 100R and 1000u cap to the power line of the 555...it seems to not allow the timing R/C to function properly.  The time constant is probably interfering or something in this application.   It was a trick I learned for use with OPAMP oscillators, notably the Easyvibe....I got about 6V straight DC output by doing this.   So there's one answer; doesn't seem to work with the 555!   Perhaps Mr. 555 dumps way too fast (no ramp...).       

The cap(s) across the power pins come from Mr. Forrest Mims III himself, tho, and they do work to help with reliability and stability.

For pics, sorry I missed that before:  getting an account at like Imgur is good.  Then you press the 'insert image' button when replying and copy/past the link to your image...

[bluzeyonecat]

I hope you get to feeling better soon. Been fighting cancer now 4 years. Feeling sick sucks. Blah! And people wonder why I dig the blues.
As far as "Mr." is concerned, it was only out of respect for your knowledge and appreciation for your time. A truthful analogy is : I'm fumbling through "Mary had a Little Lamb" and your rippin' Paganini's "5th Caprice" self taught or not.
Well I'm glad that the decoupling 100R + 1000uf have you a hard time too. At least I know I wired something right! Lol! I will be on in.a while to give the values in the other thread.
I want to play with stuff but right now my wife is out working in the yard making me look bad. Lol! Thank you all for your help and time.

[GibsonGM]

You're certainly welcome, Bluze!  Best wishes with your recovery, man...I have no complaints in the face of something big like that   You can do it!!

I'll help anyone, anytime on here, if I think I might have a little knowledge, because that is how I learned on this forum...started off with a EE buddy showing me a few things with 555's etc., and found this place, where people went to great lengths to get points across!  I only know what I learned from others.  This is an awesome place like that!   There ARE several/many guys with formal backgrounds who DO know most every property of transistors, opamps, transformers etc....I like to think they can have a break if some of us "middle men" pick up some of the load, ha ha...you will be doing that in no time!   

If you are addicted like the rest of us, the learning happens fast...

[bluzeyonecat]

Ok. I'm back! I got busy (I hate that stuff! )  Very interesting and helpful formula. I'm going to be tapping into alot more of my 390R for sure! Going to have to take back all the nasty thoughts about my parts supplier's parts being junk and remove foot from mouth. Lol!
I am still a little confused about adding the limiting resistor to the chain without having if influence what I'm trying to be variable. Forgive me. I'm sure once I realize it, I'll want to kick myself. If you could please elaborate on that.
Good news is I did get the 556 working. Both sides even! Lol! It did seem to be a bit more "noisy" than using two 555. I'm sure some caps that you spoke of earlier would quiet it down.
Which leads me to my next question, is there a way to test the value of your caps with a basic digital multi meter? I have alot of really small orange, ceramic ones and am cluelessto their uf/pf. Aside from that, once I get my head around some of this, I decided on my build. I would like to make a version of the punk console and send that signal into the Quick and Dirty filter. Should be pretty cool in a pencil box I have. Lol! Hope everyones doing well and thank you for your help.

[GibsonGM]

Hi Bluze,  yeah - the 556 may be 'noisier' just due to it having more wiring flying all over picking up junk, and also the fact it's not in a nicely grounded enclosure ("shielded").     Try the 'stabilizing caps', altho I'm not sure they'll do much for actual 'noise'....but getting it all in a proper box might!    Try to keep your wires short....and the power supply near to the chip....if you're using a plastic box, you might think about shielding it with foil inside to keep the signal 'less noisy' - but you also have to prevent your circuit from shorting to it if you do that.

TANGENT ALERT:
Re. limiting resistors....ok, look at it this way....you have an LED.   That thing really shouldn't be run much over 20mA as they burn out a bit above that (30mA, roughly, for many/most)...and mostly, we want them to take much LESS current than that, for battery longevity.  Personally, I'm more of a "less than 10mA" guy most of the time, depending on the LED efficiency.  Anyway...   

So, we say "hey, I want to allow only 15mA to go thru this LED, max.  My LIMIT for it.  No more.  I am in control.  How do I do that?"  The LED, wired right to 9V, will turn on - it has a miniscule internal resistance when on, allowing a lot of current to flow, and it commits suicide.

So, I use Ohm's law, current in Amperes = Voltage/Resistance.     For a 9V circuit, you get 9v/.015A = 600 ohms.   So you'd grab something pretty close from the standard values, perhaps a 560 ohm if the application isn't critical.  It's not here, so that's fine. *

BUT - "I want to be able to turn the LED DOWN, too".   So you wire your pot in after (or before) the resistor, as a variable resistor (1 lug tied to wiper as input, other lug as output).   Now you can turn the voltage DOWN, dimming the LED.  You can't turn it up any more than to the point where it's limited (pot = zero).  The maximum current that can flow in the circuit here is already set by the 600R, and is .015A, or 15mA.    That is .135W, less than the pot's rating of .25W, so it is safe.   

IOW, if you turn the pot down to 50 ohms resistance, with no LIMITING RESISTOR there, you have 9v/50 ohms = .18A, or 180mA.    Voltage x current = Power in Watts.....9V * .18=1.62W....the pot smokes and dies without the limiter.     If you have the limiter in place, when the pot is 50 ohms or what have you, you now have 610 ohms in series with your LED....the current is limited to a value under the rating for all of your components (LED and POT), cannot go any higher, and the stuff is safe.   

If you have more questions on Ohm's Law, and/or Watts Law, maybe start a new topic "Ohm's law for noob's? " or something?  Nothing to be ashamed of, it takes time, but it's also KEY to understand these as you move forward!   


If your meter doesn't have a cap test function, you might get a cheap capacitance tester on Ebay, they're like <$20 and are worth it, IMO - they do transistors, diodes etc.

*In reality, we use a little 'formula' for setting up the LED, which is "Voltage Supply - LED Vf /  LED current" which I ignored above for simplicity.

[duck_arse]

So you wire your pot in after (or before) the resistor, as a variable resistor

a point here lot's of people forget or overlook is that current is the same in a series circuit. in this case, the series circuit consists of the lad, the current limit resistor, and the pot. so, it doesn't matter in what any of these three parts are wired, because the current through each is the same. the voltages across each component in the series string differs, according to Mr. Ohm, whom I believe you've met.

Which leads me to my next question, is there a way to test the value of your caps ...?

[walked myself into a trap here, but] get a rotary switch, and hang a bunch of different known/marked value caps on it, and hang that off one side of your 556, wired as an astable, flashing a led. on the other side, build the same circuit, less the timing cap. now stick one of your unknown caps in, and work the range switch till you get closer/further to the same rate. it'll at least tell you pF from nF, and no meter needed.

[edit :] the above won't work quite like I was thinking. the range of visible flash-rate will be a bit too narrow in the pF/nF range.

[bluzeyonecat]

Cool! Thanks guys! Lots to think about and some studying ahead, but I feel confident having good direction.