I'm using a QRD1114 sensor for a line-follower. Datasheet: http://www.fairchildsemi.com/ds/QR/QRD1114.pdf
Im hooking it up with this schematic:
However, I'm unsure how the value for the 10K resistor was calculated? It's acting as a potential divider, right?
For the LED im guessing that the value of 220 was taken from doing:
R=(Input Voltage - Max Forward Voltage)/(Optimum forward current)