[WheelWatcher] feeding clock signal of wheel watcher into a pid controller as voltage signal

[Vatana An <rathborey@xxxxxxxxx>]

Hello Pete,
 I have a need to use a pid controller so both of my wheels can be 
controlled to move at the desired speed. My input voltage will be the 
voltage that I feed into the servo motor (which has been modify to be a dc 
motor). The wheel watcher will generate a clock signal to see how fast the 
wheel is moving and output it to the oopic-r as clock signal. My question is 
that how can I convert the clock signal coming out of the wheel watching 
into a voltage signal so that I can feed it into my pid controller? Do I 
need any extra hardware? If so do you have such hardware available for sale?
 Thank,

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Vatana An