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this instructable will show you a neat little circuit to generate PWM (Pulse Width Modulation), that is quick and easily built from components that are likely to be in your collection already!

Parts List:

  1. 1x 555 Timer IC
  2. 1x 100K Linear Pot
  3. 1x 100nF Capacitor (Ceramic or Propylene Film)
  4. 1x 10nF Capacitor (Ceramic or Propylene Film)
  5. 2x small signal diodes (1N4148/1N5818 etc)
  6. A 12V DC Power Source

The frequency of the output is dependant on the values of R1 (the pot) and C1. If you require a specific frequency, you can work it out using the following formula:

Frequency = 1.44 / (R1 * C1)

In order to drive inductive loads (motors, solenoids etc.) it is highly recommended to add a transistor/MOSFET onto pin 7 (the PWM output) -- don't forget a free-wheel diode if you do!

If you require finer adjustment of the PWM output you can always add a low value pot in series with R1 (suggested value is ~5K linear).

Hi, i want to use in for a HHO generator, is it possible.
<p>Hi,</p><p>This wouldn't be suitable for a HHO generator as it can not provide enough current to support electrolysis nor is it at a fast enough frequency</p>
Thanks fir the quick response, do you perhaps have any ideas for me that would be suitable?
<p>I would like to use this circuit to control a treadmill motor at around 100 vdc.</p><p>How would you feed that kind of high voltage into a circuit like this?</p>
<p>You would have to use a dedicated power supply unit to bring the high voltage down to something accepted by this circuit, such as 12VDC. You can then use a high voltage/high power transistor to PWM control the motor.</p><p>You would connect the base of the transistor to pin 7 of the 555, the negative of the motor to the collector of the transistor and then the emitter of the transistor to the main negative supply.</p>
I took your design and added the Treadmill motor as you see in my diagram.<br>Also changed R1 to 10K and C1 to 1uF.<br>Does this look logical to you. I'm not too boned up on tronics, I have a background in controls engineering which deals mostly in on/off states of 120VAC conditions. Tronics always seems to me like everything is going around in circles unlike controls which has a power rung and a neutral rung laid out in a ladder diagram fashion. Even the programming looks like a ladder.<br>Anyway....I'd like to build this circuit for a drill press conversion to multi-speed in my shop.<br>Did I hack it up, or am I close?<br>Thanks
<p>Very, very close!</p><p>You'll need to run the AC line through a fuse and the transformer first and then through a bridge rectifier. I also recommend adding an electrolytic capacitor on the rectifier output to get rid of the 100Hz/120Hz ripple on the DC line. Something from 100uF to 1000uF @ 35VDC rating should do nicely. I've attached a diagram to make this a little easier to understand.</p><p>Aside from that, all looks good!</p>
<p>If I under stood you correctly, this is just to feed the control circuit. I would still feed the motor from the BR that I already have in my circuit. Is that correct?</p>
The bridge rectifier from my last comment would be producing 14/15VDC tops when not under load.<br><br>The best thing to do would be add in a secondary bridge rectifier, rated for the high current of the motor, directly across the mains. I would then recommend adding a suppression capacitor across the motor too.
<p>Thanks for the help, I really apreciate it. Forgive my lack of knowledge, but your reply was as I thought would be the case. What rating should the capacitor be and should that be in parrelel with the blocking diode?</p>
No worries, I always find giving it a go is a good way to learn!<br><br>The capacitor value shouldn't matter too much, something from 22uF to 100uF should do just fine. It will need to be rated for at least 250VDC though and probably be a safety capacitor as it is directly across your mains supply.
<p>I reworked the circuit a little with all your suggestions (see attached).</p><p>I'm going to order some parts and build it, and test it.</p><p>I'll let you know how its going after I let out all the smoke, which seems like the usual with me and tronics.</p><p>Thanks a BUNCH!!</p>
Sounds good! Sometimes letting the magic smoke out is half the fun...<br><br>Obviously, play safe around the mains and good luck with your build!
I have a feeling you are missing a THR connection... Maybe a short to TRIG?
Nope, no THR connection required
Trg and Thr are internally connected to the comparators that set and reset the output. When Vtrg &lt; 1/3 Vcc the output flip-flop is set. When Vthr &gt; 2/3 Vcc the output is cleared. How is this circuit supposed to clear it's output with no thr connection?
My apologies, I haven't looked at this circuit in a while - you are correct, connect THR to TRG
<p>Do you have another design for that just with a 10K pot?</p>
<p>If you replace the 100K pot with a 10K pot, you'll have to times the value of C1 by 10 - replace C1 with a 1uF capacitor, electrolytic doesn't matter.</p>
<p>Nice design.</p>

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