555 timer – the hunt for good PWM – updated

Updated 4th/Sept/2015: Previous circuit has some flaws. This one below is now OK. Thanks to Ling for helping spot it.

PWN circuit

The circuit above DOES give a PWM signal. I verified it on my scope šŸ™‚ Click on the image for a bigger picture.

Pin 1 = to ground.

Pin 2 = Jumper it to pin 6.Ā  Also, a 4.7uF capacitor goes here, the positive side (longest leg) to pin 2 and the negative terminal (shorter leg) to ground.

Pin 3 = one wire of your speaker (doesn’t matter which)

Pin 4 = to 9VĀ  (9V was the voltage used – from a 9V battery)

Pin 5 = unused

Pin 6 = One leg of a 15K resistor goes here, the other leg into pin 7

Pin 7 = a 1K resistor (brown black red) to +5V (Vcc)

Pin 8 = to 9V

Connect the 9V rails together (suggestion: use a long red jumper, i.e. 9V to 9V. and connect + and – of a 9V battery to the power rails. Not sure if the circuit works with 5V. Will try later.)

Connect the two ground rails (suggestion use a long black jumper)

TheĀ pot (a 10K pot is good here) attaches to each leg of the 15K resistor – You should use crocodile clips for this – to an outer pin of the pot (it doesn’t matter which outer pin). The other leg of the resistor has a different crocodile clip going to the central pin of the pot.

Thanks to Ā Dorian McIntire. His video is here: https://www.youtube.com/watch?v=m1lDBUWdfKE

The next circuit described below is not-PWM but it gives good tones nonetheless :).



This circuit http://www.reconnsworld.com/audio_tonegenerate.html works well at giving an adjustable tone but from my investigation of it, it isn’t PWM generated. I took my scope and analysed the output (pics maybe to follow later). When I adjusted the tone, the peak stayed exactly the same. It didn’t broaden (or shrink) like a PWM signal does.

Instead, the new tone was created by just adding more pulses; examination of the sound spike or “pulse” showed that the pulse stayed exactly the same – it’s “duty cycle”, i.e. the width of the pulse didn’t change. So if you don’t care whether your tone generator is PWM or not, then this gives quite a good range of frequencies.- but it’s not PWM based as far as I could tell.


One thought on “555 timer – the hunt for good PWM – updated

  1. If you wanted to use the PWM circuit at the very top for controlling a motor, then you would need to modify the circuit. Motors contain “coils” which can give off “inductive spikes” (large currents due to coil inductance) and damage components in circuits (especially IC’s !) so you would have to modify the circuit. The video below shows a PWM circuit for a motor:
    https://www.youtube.com/watch?v=Cal0sDwYB_w by PawnozTV


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