I am using an Arduino Pro Mini to detect a PWM signal from a radio control receiver. The input pin on the Arduino is supposed to be limited to 20mA current with a max current of 40mA. I plan on using a 220 ohm resistor in the circuit. Do I need a .1uF cap to ground (and what kind of cap)? Adding a cap seems like it will smooth the signal and make it more of a constant voltage signal. The following is part of my circuit so far. TIA

 

The current limit is for outputs. Inputs are high impedance, and you don't need the resistor. I don't think you need the cap either. That would slow it down, and RC servos are completely based on timing.

 

If you are converting PWM to a DC value, see attached for filter design
recommendations.


Regards, Dana,

 

I assume that you are using a signal from ta servo output on an R/C receiver. That pulse can be either positive or negative going, depending on the receiver you are using. Most nowadays give a positive pulse. The pulse will very in width from approximately 1mS to 2mS and will occur about every 18mS. You can connect the signal directly to the Arduino input pin to measure the length of the pulse. Use the "pulsein" command for this. For details see the url below:

https://www.arduino.cc/en/Reference.PulseIn