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Triangle-wave oscillator, or just one shot generator?

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2/9/2001 7:01 PM

Triangle-wave oscillator, or just one shot generator?

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#func.gif

or http://www.eed.usv.ro/misc/mirrors/cc/circuits/circ0280.htm

(same schemtaic-thanks Zach)

Is this only a one shot generator? Is there any way to make it into an ocsillator? I'd like to try this in an auto-Doc (nice name eh?) or Tremolo circuit...I don't think this would have the clicking problems associated with square wave generators.

Thanks for your help,

Krusty.

2/9/2001 9:42 PM

Triangle-wave oscillator

a one-shot is an entirely different animal. this is an oscillator... choice of triangle or square-wave output, with a single-ended supply (good for one 9V battery operation) and dc offset on the triangle/square wave that can be removed with a blocking capacitor (+ towards circuit output, choose a size based on the value of 'c' you are using). for lower frequency oscillation, try using 100k-1M for r, 10uF-1uF for c.

zachary vex

2/9/2001 10:13 PM

Thanks Zach. Good this is what I wanted to hear, that means that I made an error putting it together. All i got was a one shot, I'll try it out then complete this post...

...okay i'm back...still no go i'm using 560k for R and 4.7uF caps...I've tried all the permutations of cap polarity, to an LED for testing. Each time the blocking cap is reversed i get a pulse. Should the second cap be somthing different in value? Would voltage readings help debugging? I'm running two 741's on a 9V fresh battery, yea, I splurged.

Thanks,

Krusty.

2/9/2001 11:33 PM

are you limiting the current to the led to 10 mA max (preferably less)? be sure to put a series resistor in there or you'll draw too much current. probably 1.5 or 2 k should do. try the square wave output too... does it die with the led on or off? you may have to watch it's output with a scope or meter instead, because the led might be continuously lit by the bias on the output (it is floating around 4.5 volts and the waves rotate around that point, because you are using a single-ended supply.) you'll need to figure out some way to get the voltage down to the range you need it at for controlling the led... perhaps a string of leds or diodes in series would drop the voltage enough, or maybe even a big enough resistor, or maybe a largish cap in series with the output would let you see the led rise and fall with the oscillator. you may have to increase the size of the wave also by changing the 47k resistor going from the one op-amp's output to the other op-amp's input... i am a hack, and i'd fix this by hacking at it. RG can dissect the circuit for you quickly and tell you how to make it work, most likely. but i'd suggest playing hunches until you have a personal relationship with the circuit. 8^)

maybe put a blocking cap on the output, say 10 uF, and then plug it into an amp turned down pretty far. use a 1Meg or 100k pot for the R value and turn it until you hear the triangle wave working. then go from there trying to get the led into the operating range.

zachary vex

2/10/2001 12:48 AM

Hehe, okay I'll try to develop a closer relationship with it. I guess I might as well try implementing it in what I want instead of concentrating on the LED...i want to use it to drive the filterof a Dr. Q. And then a tremolo pedal. Do you know how to make an envelope controlled tremolo? In the end I want a modulation type box that has tremolo and Dr. Q type filters, operatable by pedal, LFO, or envelope follower.

...after a couple minutes tinkering with the LED...

I got something going at first it ramped up when i turned the pot, and ramped down when the pot was twiddeled the other way. Not much use (except a nice fader!)...this is all without that extra capacitor. I changed the C cap to 47uF. I've got a 6k resistor from the output to the LED. Then under the influence of some unkown force (it might just be love

) i change the R resistor from the output of IC2 and inverting input of IC1, to the output of IC2 and the NON-inverting input of IC1...and It's working, or at least oscillating, i don't think it's a triangle wave though...square wave output works now too...similar to triangle output, that is until i changed the 47k resistor (changes speeds). The 10k symmetry pot has to be "just right" with a little tender loving care...I think we've now solidified out relationship. Though just like women, i don't understand it.

Any more help is appreciated, as I don't think it's ramping up or down as it did with the pot. I think i'll try it with the filter as I await the next response.

Thanks,

Krusty

2/10/2001 3:17 AM

quote:
"Do you know how to make an envelope controlled tremolo?"

one of my first inventions was something i called the dynatrem (i even had a friend do all the artwork up for screening boxes, but never used it). the harder (louder) you played the faster it went, and as the signal died out it slowed down. i gave up on it when i realized it wouldn't fit in a 1590B and it drew too much power (over 20 mA, against my rules.) i know more now, but i just don't feel that excited about going back... ever onward, for me!

i'm sure if you stick with it you'll get what you want out of the circuit. if you want to control the speed of the trem (once you get one working) with the envelope of the guitar volume, that seems easy enough to put together... take the envelope controls from a Dr. Q or whatever is easiest and use the variable resistance device that controls the filter(it may be a vactrol or even a transconductance amp, i dunno) to control the trem speed on your trem instead. voila! it's just a matter of tweaking until you get the speeds right. sounds like it could be fun. if you start with an envelope detector from an auto-wah that already uses a vactrol, you'll just be putting the vactrol's output where the R is in the trianglewave generator you are tinkering with now.

if you need to drive an led with that circuit you are working on, don't be afraid to add another component to your wave generator's output before the led... maybe a transistor driver would work. look for led drive circuits you can nab from other circuits that cycle an led's brightness... heck, you might find a better led driver for your trem in an actual trem circuit!

one thing to keep in mind when you are trying to make things work that you don't fully understand... it may be working, and you don't just notice it. or it may be so close to working that you can almost taste it, but you need to INCREASE a value that you were certain should have been decreased, or turn something upside down and connect it to the positive rail rather than going to ground (like your led). you never know. i cyclically subsititute inverted PNP/NPN transistors or fets or mosfets when i have a hunch i need a driver but don't know what... just keep in mind that the emitter likes the positive rail in a PNP and likes the negative rail on an NPN. i get lucky... it's a war of attrition to eliminate everything that DOESN'T work.

now, i'm off to the lab to do it some more. i need to raise board space on my new invention by one-half square inch... to do it, i have to eliminate the two most expensive support components on the board (biggest, too.) so far, no luck, but do i care? hah! i spit on failure. plegh! i try, try, try, try, and try again. sheer perseverance is the only method that truly works. how do you think people figured out how these things worked in the first place? 8^) the person who quits first FAILS. the person who keeps working while the rest of the world sleeps gets to plant the flag at the top, hopefully before his oxygen runs out. keep breathing.

zachary vex

2/10/2001 7:03 AM

Triangle oscillator...and finally Auto-Doc is working!

Well good luck with your endevour...I definately work while the rest of the world sleeps...this board gets really dead after 3:00 am here (8:00 am forum time).

I did get an interesting effect with the LED when I put a cap near it (I forget where now)...off/bright/dim/off/dim/off/bright/etc...

One question about these variable resistors:

What's the difference between a vactrol/varistor/optoisolator/LED&LDR?

And I've got no idea about a transconductance amp.

...back from tinkering for 20 minutes...well it stopped working since I last played with it, must because my dog walked on it and kicked over my whole box of capacitors (recently organized too). So i've been trying to get it back to its previous state of square-waveness, but what do you know, it's doing nice smooth triangle wave now!

For everyone's reference (and mine especially)...I'm using a 0.47uF (connected as per schematic, changed from previously 47uF) and a 1meg (or 2.2 meg for slower rate, pot across it for variable speeds) resistor for R. 6k resistor from triangle out directly to an LED going to negative (an LED to positive works too, just don't try both of them together!)...

...Another couple of minutes tweaking...Perfect! I've got my Auto-Doc working beautifully!! Peak, range, and speed all variable!

So if I were to change this filter to a "no-pass" it would be tremolo (though with an envelope contol filter it wouldn't control speed, I think it would be nice attack delay!!)...and other kinds of filters will also work then too. And switchable from trianlge to square wave (though probably have to put a small value cap to get rid of clicking). So if I can get a little help with the different kinds of filters, and put on enough switches I'll be able to have a multi-filter modulator, controllable by envelope, LFO, and foot (if I connect an external Pot).

Sweet, Sweet!

Thanks for your assistance Zach, greatly appreciated!

Maybe I'll post some sound samples and even a schematic if I get this all done.

You think I could even add another section that uses the envelope to control speed of oscillation instead of amplitude? Overboard is the way to go!!

Thanks again,

Krusty!

(can't you just tell i'm stoked, even at 2:00 am!!)

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