Optek OPB625 Optical Swtich

[squide]

This is probably a no-brainer... How do I connect the cathode and anode pins on this sensor to the FRC? Here's the datasheet:

http://www.optekinc.com/pdf/OPB625.pdf

I have pins 2, 3, and 4 connected to the FRC counterparts, but I'm unsure about 1 and 5. Thanks!

[Kevin Watson]

This is probably a no-brainer... How do I connect the cathode and anode pins on this sensor to the FRC? Looks like you can safely run about 20mA through the LED (maximum is 50mA per page one). Then looking at the top-center graph on page three, it looks like the corresponding forward voltage at this current is about 1.3 volts. Since it would be handy to power the LED from the built-in +5 volt power supply, you need to find a resistor that will drop 3.7 volts (5 - 1.3) at 20mA. Plugging this into ohm's law, the value of the resistor should be 3.7/0.02 = 185 ohms. The closest resistor with a 5% tolerance is 180 ohms. Now you need to know the power rating of the resistor. Using the equation P = I^2 * R, the resistor will need to be able to safely dissipate 0.072 watts. Adding some margin to that, I'd go with a 1/8th watt (or larger) 180 ohm resistor, wired in series with the LED. The cathode side (labeled 'K') goes to ground, the Anode side goes to +5. The resistor can go on either side of the LED.

-Kevin