I (theoretical physicist, all the basic theory, no further electrical engineering background) am just diving into Arduino and I have a very basic question:
I am playing with a Zilog ePIR motion detector (https://www.sparkfun.com/products/9587) in hardware mode. I would like to use a fixed resistor to supply a voltage of, say 0.2V to Pin 3 (DLY), to set a delay for the motion detection switch-off (the whole thing runs on 3.3V). From Kirchhoff's voltage law I would think that I need the internal resistance of the module to calculate a ratio with the series resistor. I am getting R = R_Module*(3.3V-0.2V)/0.2V. However: I don't know any internal resistance, nor can I measure any between GND and DLY. How do I calculate the needed resistor? Am I thinking totally wrong?
I am using the circuit from http://macherzin.net/article17-Arduino-Sensoren-Infrarot-ePIR Bonus question: How did the author know that he needs an 80 Ohm resistor if he connects the module to 5V?