AN-1158 Rotary Encoder to Analog Converter

In the past, Direct Current (DC) motor speed sensing was done by using a tachometer which converts speed directly to DC voltage. An analog Proportional-Integral-Derivative (PID) controller took this voltage and compared it with a reference voltage to generate a command signal to speed up or slow down the DC motor. But more recently, the method for speed feedback employs optical encoders which generate pulses instead of analog voltages.

With this, microcontrollers are used instead of analog PID controllers. A microcontroller receives the input pulses, transforms them into digital feedback signals, compares them with a digital reference and feeds it a digital control algorithm to create a motor speed command. All this adds additional hardware and requires software for motor speed control. The GreenPAK™ implementation shown is a Pulse–to–Voltage converter and can save this hardware and software cost, and an analog PID can still be used with DC motors having encoder feedback.


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