Homebrew PCBs

Okay, I have uploaded a file named SingleChipPWM.pdf to the Files section. It has the schematic and a brief explanation of the circuit. I have built the circuit as shown, using 2 op-amps from an LM324 quad op-amp IC and a 12 volt single-polarity power supply. I have also built essentially the same circuit using 2 comparators from an LM339 quad comparator IC, using both 5 volt and 12 volt single-polarity voltage supplies, but with the addition of pull-up resistors, since the LM339 uses open-collector outputs.

Theoretically the circuit should work at a wide variety of voltages without altering the frequency or PWM set by the potentiometers (RV1 and RV2, respectively). I would presume it could be built with a dual op-amp chip just as well, and using split-polarity power supplies.

I'm guessing that Steve will encourage us to take further discussion of this over to Electronics_101, since this is more about circuit design than about PCB production ... :)

--- In Homebrew_PCBs@yahoogroups.com, <casy_ch@...> wrote:
>
> It would be nice if you could put it into the file or photo section of the group. Thank you.
> 
> Jean-Claude, Switzerland
> 
>   ----- Original Message ----- 
>   From: Roger Blair 
>   To: Homebrew_PCBs@yahoogroups.com 
>   Sent: Saturday, May 01, 2010 5:36 PM
>   Subject: RE: [Homebrew_PCBs] Re: Speed control for laminator motor
> 
> 
>     
>   I am interested in this also, if you don't mind sharing.
> 
>   Thanks,
> 
>   Roger
> 
>   From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com] On Behalf Of awakephd
>   Sent: Friday, April 30, 2010 07:38
>   To: Homebrew_PCBs@yahoogroups.com
>   Subject: [Homebrew_PCBs] Re: Speed control for laminator motor
> 
>   Richard, what kind of circuit do you have in mind for the PWM? If you're wanting to do something with discrete ICs rather than a
>   microprocessor, I put together a PWM controller that allows for variable frequency as well as variable pulse width (true PWM) -- and
>   it only requires 2 op-amps or comparators, so it can be made with a single chip (not counting the drive circuitry). This may be a
>   common design -- I may have re-invented the wheel! -- but I couldn't find anything like this when I was needing this circuit. I
>   specifically wanted something that generated true PWM, but allowed me to vary the frequency so that I could choose the best
>   frequency at which to run for a given application. Let me know if you're interested.
> 
>   --- In Homebrew_PCBs@yahoogroups.com <mailto:Homebrew_PCBs%40yahoogroups.com> , Richard Spelling <rls@> wrote:
>   >
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>   > 
>   > Went to bed tired and annoyed I couldn't easily find a slower gear motor
>   > for the laminator.
>   > 
>   > Dreamed about building a magical speed controller that would let me run
>   > the existing motor infinitely slow.
>   > 
>   > Realized I could use "temporal kinetic and thermal stabilization" since
>   > it's a worm gear motor.
>   > 
>   > I.E., I build a standard PWM controller but set the frequency real
>   > sloowwwwww.
>   > 
>   > Imagine having the speed turned down real low. Along comes a pulse. The
>   > motor spins up and turns the worm screw a revolution or two, then spins
>   > down. The board advances a fraction of an inch. An in-determinant amount
>   > of time later, along comes another pulse.
>   > 
>   > Yes, it's "jogging" the board forward and not continuous motion, but
>   > between jogs it sits between the rollers long enough for the heat to
>   > transfer through the paper.
>   > 
>   > I'm thinking about 10Hz.
>   > 
>   > Whatcha think? Just another crazy idear from Richard?
>   > 
>   > Now I just need to build the board.
>   > 
>   > Wait a second, I need my laminator to build the board to fix the laminator!
>   > 
>   > 
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>   > rcgAnjxf1FYgfzIrYMy3PBHKB2I1CcW6
>   > =z+Py
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>   
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