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I'd like to construct a device which can control a servo in one of two modes - passthrough the original signal, or override with own values.

Am I correct in thinking that I can just smooth out the original signal with the right resistor and capacitor and treat it as an analog input?

More context:

I've already got a typical RC model receiver connected to the servo itself. I'm planning to insert maestro mini in between, with original signal attached as an analog input.

Now, according to the datasheet, that servo controller reads the analog input at 20kHz, which seems like it wouldn't catch the expected level, but rather a single point from the PWM signal. Is my capacitor idea enough here?

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As far as i know , the accurate way of capturing such signal is to use the input capture ( Timer module ) in a microcontroller .

The reason analog read after using an RC filter wouldnot work IMO is that the Servo signal works between 0% to 10% duty cycle at 50Hz , that means even with filtering of multistage low pass filter you will have a hard time reading correct values because the resolution is low (steps)

You might also find high resolution ADC (more than 10bits) reading difficult because of noise issues.

check this figure to see what i mean filtered PWM

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