Hello! I'm using Adafruits MotorShield to control the speed of a cassette walkman. Despite using 64khz for the PWM I'm still getting that horrible audible whining from the motor! Is there a simple solution to this or is it a tricky and costly one? Thanks, Goatboy
Don't use PWM but smooth it and get a variable DC voltage, then there is no audio from the motor.
Don't use PWM but smooth it and get a variable DC voltage, then there is no audio from the motor.
Sorry for not understanding but what do you mean"smooth it" and if I were to use variable voltage can I still use the arduino?
If you connect an electrolytic capacitor across the output you will filter out the high frequency signal that is generating the interference. The motor speed can still be controlled because the smoothed voltage will be a DC value proportional to the PWM output. The value of the capacitor depends on the motor current but start with 100 microfarads and work up till the interference stops.
That sounds easy enough! When you say across the output do you mean at the terminal or can I attach the capacitor to the motor directly? I know I'll blow myself up one of these days ;D
You can attach it to the motor although it will be more effective if its connected across whatever is driving the motor. The negative lead from the capacitor goes to ground (or the negative side of the motor).
Electrolytic capacitors are marked with a maximum voltage rating, choose one appropriate for the motor voltage.
Will try it now!! Thanks for your help Goatboy
Interesting :-? It did reduce the sound but I got some immense crackling like static plus the speed wasn't stable. Is it the case that the higher the capacitor value the more current drawn because the h-bridge on the MotorShield heated up quicker. Could it be that the MotorShield is already using smoothing and adding an extra capacitor is interfering? Goatboy
Actually I'm getting all those problems now without the capacitor so I better start again!
Must of buggered the walkman!! But I tried it out on an ordinary motor and it works a treat! I'm glad I bought that box of capacitors now! ;D Thanks
what happened goatboy?
did you make your microcontrolled walkman? sounds a cool idea, i used to do this manually with a variable psu off a Hornby train set, the sounds were great being from cassette tape. real smooth. ( i used an old sony walkman)
made lots of strange sounds lol : P
just wondering if you got rid of the crackling..interference.
Christ! That brings back memories qweety! I've been skipping from one thing to the next with all the arduino world. But yeah, I remember trying to get a solution for the noise picked up by the circuitry and I don't believe there is a cheap solution I'm afraid. I love the idea of tape and using multiple cheap walkmans to play with sounds so I'll get around to it again but the motor always becomes noisy when you really slow it down!!! :-/
so you're using tape + the magnetic heads as a instrument?
i used to work with the guy that invented the first endless loop mellotron!
-sj