Help with 555 timer PWM

Thread Starter


Joined Aug 14, 2012
Hello gurus

I am trying to learn about PWM and got a circuit from here. Now I have assembled the components on a solderless breadboard. My first attempt did not work at all. I had checked everything I can think of. I started again from scratch, now it works but the pot isn't doing squat. The motor just runs. The motor I am using is this one. My question is simply: Is this schematic correct or am I doing something wrong? I must add that I'm not entirely sure what to do with the wiring around pins 4, 7 and 8. Currently, I've got the 10K resistor from the line where 7 is bridge to the line where 8 is, and then 8 bridged to 4, 4 bridged to +12v and then also bridged to ground with a 0.1uF capacitor. I don't know what the circles at pin 4 and the +3-18 at the top mean. Any help would be greatly appreciated. Thanks

John P

Joined Oct 14, 2008
I suggest that you put an LED, with a resistor in series with it, connected to Gnd from pin 3 of the 555. That way you can verify that the output really is doing what you expect, which you can see by the brightness of the LED. If there's anything wrong with the FET or the motor, you can't separate that from the action of the 555, so you need a diagnostic method.


Joined Jun 30, 2011
The +3-18v at the top is your voltage input.

You'd have your 12v here.

4 and 8 are connected directly to your 12v rail. C3 is a bypass cap so needs to be close to pin 8 and pin 1. Pin 7 is your output, the 10k resistor is there (I think) to make sure the Mosfet switches off properly and doesn't stay open.

You should really have a diode across the motor and possibly a electrolytic capacitor across the power rail as seen in this example.