Hello,
I found a circuit that works well for 12v motor control using PWM driven by an LM324, but I'm now hearing the pulse wave on the audio output.
The motor controller is for a tape player to get variable speed. However, I'm hearing a variable pulse width around 85Hz almost as loud as the audio on the tape.
Putting a diode in series feeding the + of the motor helps, but not enough. A diode and capacitor across the motor doesn't help the hum at all.
I've heard of the pulse being audible in the motor itself, but can't figure out how it's making its way to the output. Could it be because the audio circuit and motor circuit share the same ground and + supply? If so, is there a way to isolate?
I suppose I could try a notch filter, but I don't know how well that would work.
Thanks!
I found a circuit that works well for 12v motor control using PWM driven by an LM324, but I'm now hearing the pulse wave on the audio output.
The motor controller is for a tape player to get variable speed. However, I'm hearing a variable pulse width around 85Hz almost as loud as the audio on the tape.
Putting a diode in series feeding the + of the motor helps, but not enough. A diode and capacitor across the motor doesn't help the hum at all.
I've heard of the pulse being audible in the motor itself, but can't figure out how it's making its way to the output. Could it be because the audio circuit and motor circuit share the same ground and + supply? If so, is there a way to isolate?
I suppose I could try a notch filter, but I don't know how well that would work.
Thanks!