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 Forum index » DIY Hardware and Software
Lm311 comparator circuit for synth diy??
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loss1234



Joined: Jul 24, 2007
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PostPosted: Mon Sep 08, 2008 4:13 pm    Post subject: Lm311 comparator circuit for synth diy?? Reply with quote  Mark this post and the followings unread

can ANYONE help me find a circuit for using an LM311 to turn NON cmos friendly stuff into square waves?

i know oakley had a dual comp with the 311 but i cant find any schematics and so many other projects just use opamps as comparators.

i figure using something like 5M as positive feedback for hysteresis? does this sound right?

all i want is to use a pot as a volt ref and compare that to my input..mainly i want to be able to run NOISE and sine waves through it which will then feed into the clock of my counters.

thanks

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frijitz



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PostPosted: Mon Sep 08, 2008 5:25 pm    Post subject: Re: Lm311 comparator circuit for synth diy?? Reply with quote  Mark this post and the followings unread

loss1234 wrote:
can ANYONE help me find a circuit for using an LM311 to turn NON cmos friendly stuff into square waves? ...
all i want is to use a pot as a volt ref and compare that to my input..mainly i want to be able to run NOISE and sine waves through it which will then feed into the clock of my counters.

Are you sure you need an LM311? This is a super-high speed device that is used for applications like discharging the cap in a Saw VCO. I don't think you need this kind of speed for what you are talking about.

If an opamp isn't fast enough for you, you might consider the LM339/LM2901, etc. family. These are inexpensive, low-power quad chips. For a circuit you could use part of my TGTSH circuit:
http://home.comcast.net/~ijfritz/ch_cir3.htm
All you need is the circuitry around the 2901 (leave out the modulation) and around the transistor producing the Gate signal.

Very Happy

Ian
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loss1234



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PostPosted: Mon Sep 08, 2008 7:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey thanks IAN

I am really trying to get a circuit going that will turn things into squarewaves..maybe with a pot to control the width.

i of course have the TGTSH but was looking for an ultra simple device to put before a counter (i was reading in electronotes that NOISE put through a comparator and then into a counter can be really interesting...

and i have also been enjoying YOUR articles in all those electronotes

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jnuaury



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PostPosted: Mon Sep 08, 2008 11:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

the MFOS noise cornucopia does use a window comparator on white noise to get the "grainy" noise (i dont think it uses a 311 though) then it goes through a CMOS divider to get its random gates (i have different divisions pulled out to separate jacks to do syncronized random gates)


ive found window comparators (two comparators - team work!) to be much more useful than a standard comparator. not only do you have more control over the width and positioning of the pulses but you can use multiple window comparators on the same input to get some nice sounds

ian's 5pulser is equivalent to a stack of 5 window comparators! i like sending one longer envelope through the 5pulser and using the pulses to trigger a much shorter envelope. the result is one macro-event with up to ten little micro events contained within it


i really need to do up another 5pulser but in addition to that id like to build some simple window comparators to have individual control of the pulses for structuring events and also so i can free up the 5pulser for its intended audio duties


i know i didnt exactly address your question but ive been getting excited over window comparators lately and had to get all that off my back
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loss1234



Joined: Jul 24, 2007
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PostPosted: Tue Sep 09, 2008 3:28 am    Post subject: Reply with quote  Mark this post and the followings unread

hmmmm

windows eh? sounds very promising. i have a home-made cornucopia on my modular and i lcve it...maybe i will take a look at those schematics.

dreaming of a 5 pulser...i gotta start doing more waveshaping....

thANKS

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frijitz



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PostPosted: Tue Sep 09, 2008 6:27 am    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
i of course have the TGTSH but was looking for an ultra simple device to put before a counter

I must not have explained that very well. Sad

I said use **part** of the TGTSH circuit. You ask for a simple circuit. Can't get much simpler that a quarter of a chip plus a transistor.

Very Happy

Ian
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loss1234



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PostPosted: Tue Sep 09, 2008 6:31 am    Post subject: thnx Reply with quote  Mark this post and the followings unread

no no it wasnt your fault

you explained everything very well as usual


i totally understand it is simple. WHAT I MEANT was that the reason i did not ORIGINALLY think of my TGSH unit, is that the FULL circuit is complex. but you are so right that i could take a small part of it and use it for what i need.

so this WILL make square waves, and the pot will change the duty cycle?

(is this called adjusting the duty cycle or the pwm?)

thanks as always

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loss1234



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PostPosted: Tue Sep 09, 2008 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

hmmm

if i dont have a 2901 are there any other single supply comps that might work?

thanks

let me see what i can find.

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frijitz



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PostPosted: Tue Sep 09, 2008 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

jnuaury wrote:
ive found window comparators (two comparators - team work!) to be much more useful than a standard comparator. not only do you have more control over the width and positioning of the pulses but you can use multiple window comparators on the same input to get some nice sounds

Here's another circuit I played around with some. I haven't seen it anywhere except in a physics research paper.

You make a Schmidt trigger with a relatively small hysteresis (I forget, a volts or something.) Then you feed noise into it through an attenuator! Shocked Shocked

When the input signal is attenuated, then only the tippy-top of the noise signal fires the output. When the input is unattenuated then most of the noise wiggles fire the output. The result is Lorentzian noise (Never heard of it? Smile -- it has a transition between white and pink at a crossover frequency set by the threshold point.)

Anyway, it's just a pot, two resistors and an opamp. You guys that like lots of noise sources should definitely try it. Similar to the window comparitor idea, but much simpler.

Very Happy

Ian
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frijitz



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PostPosted: Tue Sep 09, 2008 6:55 am    Post subject: Reply with quote  Mark this post and the followings unread

jnuaury wrote:
ian's 5pulser is equivalent to a stack of 5 window comparators!

Right. The LM3914 LED driver is nothing more than a stack of ten window comparitors (with adjustable threshold). As I have mentioned before, there are zillions of potential waveshaping/signal processing applications for this chip. For example, why not just feed it noise and see what comes out of each stage?

Very Happy

Ian
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loss1234



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PostPosted: Tue Sep 09, 2008 6:59 am    Post subject: Reply with quote  Mark this post and the followings unread

hmm now you have my head spinning with new ideas!

now i take it i cant use a schmitt trigger cmos (like a 40106) for the noise with attenuator idea right? it must be an opamp schmitt with hysteresis..i should be able to find one of those in the opamp cookbook

and i might need to get out my LED chip to play around with.

ok, i found a whole tube of lm2903's will those work OK?

thanks IAN

WHEN ARE YOU GOING TO WRITE A BOOK??

heck, i mean even just doing a book of what is on your website (the stuff that used to be on it and the stuff that IS on it, plus all your EN articles, and some new stuff and stuff we might not know about...i would buy it!

or we could just do a lending library Smile

thanks

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loss1234



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PostPosted: Tue Sep 09, 2008 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

ok just to check

on the COMPARATOR CIRCUIT FROM THE TGTSH

i can leave out the 330p cap and everything after it right (since this for the trig section) or do i still need that stuff? and if i leave out the mod pot, do i still need the 33k and 2.2n?

what does the 3.3k resistor to +v do?

also are you running this comp off of +v and gnd or +v and -v?

and lastly, since i want to use this as an input to a CMOS counter (as clock) do i need to do anything to the gate out signal? (add a cap, etc)



thanks

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frijitz



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PostPosted: Tue Sep 09, 2008 7:46 am    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
on the COMPARATOR CIRCUIT FROM THE TGTSH
i can leave out the 330p cap and everything after it right (since this for the trig section) or do i still need that stuff? and if i leave out the mod pot, do i still need the 33k and 2.2n?

Correct. Leave out the 330 p and everything connected to the right of it. Keep the 33k and 2.2n. You may need to change the 33k to get the threshold range you want.

Quote:
what does the 3.3k resistor to +v do?

It's a pullup resistor. The output stage of the comparitor will not work without it

Quote:
also are you running this comp off of +v and gnd or +v and -v?
and lastly, since i want to use this as an input to a CMOS counter (as clock) do i need to do anything to the gate out signal? (add a cap, etc)

Bipolar supply for the comparitor. (You might want a negative threshold for a general input.) And oh, the 2903 is the dual version of the 2901, so same circuit. The Gate output should drive any logic chip directly. I'd probably add a 10k series resistor for safety just when breadboarding.

Very Happy

Ian
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loss1234



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PostPosted: Tue Sep 09, 2008 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

a few things....i had to change the +v resistor going into the transistor to 1k...at the original value it would NOT fire my ADSR or trigger my divider...also, when i hooked the comparator up to +/- v instead of just +/gnd, it was very hard to get the comparator to have a wide range (from none to on)

i tried bigger resistors in place of the 33k..all the way up to 470k...still not a good range.

what did i do wrong? for now i have gone back to +/gnd


also, how can i drive an led off of the ouput? if i hook one up, it drains away the gate signal Sad

i think i might need a transistor buffer but i cant remember how to make one.

thanks so much

this is a great great circuit


i might build up a board of 4 of them


you have been so much help too


thanks

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loss1234



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PostPosted: Tue Sep 09, 2008 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

GOT IT

took an out from the emitter....then put that into an emitter follower

out from that i took a 1k into an LED

now i have

a jack before the transistor (for square wave)
a jack from the GATE out (post transistor)
and an LED

i also added a 100k fine tuner


this is awesome!!

i am currently making weird sounds with counters and noise AND SINE WAVES!


oh life can be so good


thanks

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frijitz



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PostPosted: Tue Sep 09, 2008 9:59 am    Post subject: Reply with quote  Mark this post and the followings unread

loss1234 wrote:
a few things....i had to change the +v resistor going into the transistor to 1k...at the original value it would NOT fire my ADSR or trigger my divider...

The circuit should put out a 5V Gate. This is the usual standard. No, it won't drive CMOS powered off of 12 or 15V. Ideally you should have an interface for that to maintain the standard levels. But jacking the Gate up a bit as you did will also work OK.

Quote:
also, when i hooked the comparator up to +/- v instead of just +/gnd, it was very hard to get the comparator to have a wide range (from none to on)
i tried bigger resistors in place of the 33k..all the way up to 470k...still not a good range.

That can't be right. Did you remember to connect the pot to +/- also? You should get a +/-9V or so range. Check the voltage at the (-) input of the comparator. You are loosing half of your gate-width range if you power +/0.

Very Happy

Ian
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loss1234



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PostPosted: Tue Sep 09, 2008 11:03 am    Post subject: Reply with quote  Mark this post and the followings unread

hmmm..i will do some tests...yes the pot is definitely at +/-

this is only on breadboard..when i move this into my modular it will be running off of +/- 12volts.


was this originally made for 12 or 15 volt psus

yes the cmos i am running is all being driven by 12 volts.

thanks

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Last edited by loss1234 on Tue Sep 09, 2008 11:09 am; edited 1 time in total
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loss1234



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PostPosted: Tue Sep 09, 2008 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

i will check the gate level with a volt meter later to make sure i am getting +5

just realized i am actually using a +/- battery psu which is only putting out +/- 9volts to test on breadboard so that could be the culprit.

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haima



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PostPosted: Sat Mar 24, 2012 9:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
jnuaury wrote:
ian's 5pulser is equivalent to a stack of 5 window comparators!

Right. The LM3914 LED driver is nothing more than a stack of ten window comparitors (with adjustable threshold). As I have mentioned before, there are zillions of potential waveshaping/signal processing applications for this chip. For example, why not just feed it noise and see what comes out of each stage?

Very Happy

Ian


Sorry to dredge up this old thread, but Hey Ian! I tried this noise -> LM3914 thing... very cool Smile

I posted about it here, including a video: http://www.muffwiggler.com/forum/post-755225.html#755225
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loss1234



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PostPosted: Sun Mar 25, 2012 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

wow...what a blast from the past...thanks Ian for helping me so much in
the beginning!

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