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Multi Purpose Rotary Machine - Mulling, Welding, Pottery, Photography Turntable

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Step 17: Motor Control #3 - Closed Loop Feedback

Picture of Motor Control #3 - Closed Loop Feedback
LM393-Pinout.png
tacho pulse circuit.png

The speed control circuit I built is loosely based round one built by Saulius Bandzevičius - I have included a pdf of his schematic in this step, but also check out his write up here. It uses Arduino and the PID Library created by Brett Beauregard.

The basic principal of this closed loop system is that the Arduino takes in the AC signal from the motor's tachometer (conditioned through the LM393 chip - pinout above), to determine the actual speed of the motor and compares that against the 'set speed' - the RPM you want the motor to be spinning. It then uses a PID algorithm to determine when to send control pulses to an optocoupled triac, which in turn activates and allows pulses of mains voltage to the motor...