Op Amp PWM output

Thread Starter

mhtraylor

Joined Jul 21, 2009
11
SgtWookie, not sure I'm ready for the Navy manuals. I was in Artillery in the Marines, simple stuff :) I've read through the site's book a few times, I pick up something new every time but still trying to get it all down.

My original schematic was two different circuits from Mims' mini-notebooks tied together, apparently very improperly. I assembled it and it did dim an led, but I think I was just somehow unintentionally controlling the voltage.
 

SgtWookie

Joined Jul 17, 2007
22,230
SgtWookie, not sure I'm ready for the Navy manuals. I was in Artillery in the Marines, simple stuff :)
A Gun Bunny! :D Welcome, brohamski - I was a wingnut. ;) Went through a predecessor course to NEETs a long time ago. Only time I saw arty fire was at ITR on Camp Pen; they shot a 105 Howie. Wasn't too long after that all of the 105s were retired, as almost none of the gun books were kept up during Vietnam; they were having failures and didn't know which gun would break next.

I've read through the site's book a few times, I pick up something new every time but still trying to get it all down.
Take your time, dude. Don't be afraid to ask questions.

Try jumping into one or two of the NEETS books. They're designed to get techs through the program as quickly as possible, with very good explanations of how stuff works. Where you might run into a snag is with the trigonometry; I was stalled on that for a week back in the day until some Navy Chief basically put his foot in my keister.

My original schematic was two different circuits from Mims' mini-notebooks tied together, apparently very improperly. I assembled it and it did dim an led, but I think I was just somehow unintentionally controlling the voltage.
That's probably it. Which mini-notebook were you reading from? I have several of them around here; some of them are very old and dog-eared. The newest one I have is 10 years old.
 

Wendy

Joined Mar 24, 2008
23,415
I screwed up and loaned some of my Mim's books to a high school student while I was in college. I don't really regret it, but I miss the books. I'll replace them eventually.

You'll find this is a very patient bunch. Wookie and I are pretty constant, and the mods do a great job of keeping hecklers and other lesser types at bay.
 

Thread Starter

mhtraylor

Joined Jul 21, 2009
11
We actually had a couple of 105s at Okinawa, but I think they kept them around for show (or to let the mysterious Arty mechs play with them). But you ain't seen nothing like all batteries of a battalion 155s unloading on a grid square :)

Thanks guys for all the help. I've built SgtWookie's PWM with success, but I'm going to start from scratch and learn more theory before I start designing my own. I download the NEETs and am going to go through them. I'm sure I'll have plenty of questions.

The Mims' circuits came from the Op Amp mini-notebook: square wave generator and basic comparator.
 

SgtWookie

Joined Jul 17, 2007
22,230
OK, the "Timer, Op Amp & Optoelectronic Circuits & Projects" - in my version (2000 printing) the square wave generator is on page 78, and there are several "basic comparator" circuits that start on page 58.

The biggest problem with your schematic was that you tied one of the inputs of the 2nd opamp to +V, so the output would never change.

Forrests' schematic provided for lots of adjustments for thresholds and timing that for your purposes (basic PWM) kind of overcomplicated things a bit.

If you compare Forrests' circuit to the one I posted, you'll note that Forrests' R1, pot R2 , and R3 are replaced by my R2 and R1, respectively - the pot was omitted.
Forrests' R6 and pot R7 were replaced by R3 in my schematic.
Forrests' R4 and pot R5 were replaced by R4.

I elected to use a 2nd opamp to compare a reference level (generated by R5, VR1, R6) to the triangle waveform that occurs on C1. This way, you can get a PWM output that goes all the way from 0% to 100%, which would have been difficult to impossible to achieve with a single opamp.
 
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