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Published on Oct 9, 2010
Here we have a jog dial from a video machine which I've taken apart. It provides a quadrature resolver output (sine waves 90° out of phase) which can be used to control digital data by adding or subtracting counts from it. In my circuit I used a D flip-flop to develop a logical direction signal (one input to D, the other to CLK). The direction and one of the two inputs are then used to drive a chain of 74191 counters (three counters for 12 bits in my case). The counters then provide data to a 12 bit DAC which has a 5V reference. This means I have a 0-5 volt adjustable supply with 4096 points of precision. A piezoelectric disc is connected to the data line from the digitizer to provide auditory feedback. The control also includes an electric brake (clutch) which can be used to hold it still. In my project the MAX/MIN logic from the counter chain stops the knob when the counter is full or empty.