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Bidirectional DC motor speed controller issue?!
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R2-B2:
Hi all,

Trying to design a bidrectional DC motor speed controller for a pet project I'm working on. I've attached a circuit diagram below of what I'm working with. In summary:

1. I've got a dual ganged 100k potentiometer which is the only input, one half controls the polarity that the motor see's and the other half controls the reference voltage that a comparator is looking at for PWM (If the polarity is +ve, then the wiper references the top terminal of the pot, and if the polarity is -ve then the wiper references the bottom terminal of the pot due to the arrangement of the transistors around the second half of the pot - so the total resistance seen from the pot is only ever 50k at it's midpoint and 0 at each extremity)
2. There's a 555 timer built in as an Astable Multivibrator - making a roughly 50% duty cycle square wave.
3. The output of the timer feeds in to an Integrator in the form of a ramp generator.
4. The Integrator's output is then the Vin for the comparator.
5. The comparators output then goes via a couple of transistors that feed into the bases of a transistor H-Bridge around the motor.

My problem . . . it doesn't seem to work - nothing happens other than there being a slight smell of burning . . . I'm not an electronics expert by any stretch, but I can't suss where I'm going wrong. Would anybody be able to point me in the right direction? Really appreciate your help!

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