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Electronics => Beginners => Topic started by: RiccardoR on April 23, 2017, 08:41:24 am

Title: PWM Controller
Post by: RiccardoR on April 23, 2017, 08:41:24 am
Hi everyone
I'm new to building circuits and this site
I was looking for some help with my circuit
I am currently get a square wave out of both 555 timers , and the motor also runs.
My only issue I seem to be struggling with is that my variable resistor isn't working as it's doesn't want to vary the speed of the motor
Any help would be great
Thank you !
Title: Re: PWM Controller
Post by: jb79 on April 26, 2017, 02:32:16 pm

A PWM control for a motor can be done with one NE555 only. For example, you could use this: (

U1 should have a pullup on the trigger-input to be sure that the level is high enough if the output of U2 can't deliver the necessary current in high state. Otherwise that might cause problems.
The values of the resistors and capacitors in the schematic should be ok, could you check if you insert the correkt one on the correct position in the circuit?

You said you checked the waveforms, so you have an oszi available? If there is no error with the circuit you should see a different lengh of the pulses at U1 output when turning the poti.
Title: Re: PWM Controller
Post by: rstofer on April 26, 2017, 05:39:59 pm
U2 pin 3 (out) should have a free running square wave output.  According to one of the online calculators, this should be about 7.8 kHz.

U1 pin 3 (out) should have an adjustable width pulse, still at 7.8 kHz with a pulse width of 55 us (if I used the calculator correctly) at midpoint (5k).  At 10k the width would be 110 us. ( (
Title: Re: PWM Controller
Post by: Zero999 on April 26, 2017, 06:14:59 pm
Alternative, just use the LM393, with one half configured as an astable and the other as a comparator. The duty cycle can easily be varied from 0% to 100%.