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Yes, you can do this, but it's not 100% straightforward since you want (presumably momentary N.O. switches) to both increase and decrease the resistance. Here is one way, there may be better ways:
simulate this circuit – Schematic created using CircuitLab
I have wired Y0 to Y3 so pressing both switches at once returns the servo to the null position. ...
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The voltage across L1A is referenced to Vin not ground. It can't be easily used for feedback in that form, Q2 and associated circuitry resolve that.
Just using a divider from L1A to ground would not give a voltage proportional to the output.
The purpose of R3, Q2, I2 and R4 is to create a voltage that is referenced to ground to feed the Flyback Error ...
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For the offset compensation, Ccomp is integrating the current out of the gm amp. There's a clock and switches on the input and output of the amplifier that switch the polarity of BOTH the input and output, presumably with a 50% duty cycle.
Therefore, any offset in the amplifier increases the voltage on Ccomp during 1/2 clock cycle and decreases it during ...
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speed up-to 50 pulses per second (not critical)
pulse-width 1 to 2 milliseconds.
Build a 50Hz oscillator with a 1.5 second pulse width connect use your positive or negative voltage to skew the on-time of the oscillator, eg by appying iot to one of the timing nodes of the oscillator through a resistor.
maybe something like this:
simulate this circuit – ...
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