Surely, some of you have had the pleasure of ripping into an old printer or scanner to harvest some really cool components? Some of you have run across some nice stepper motors, power supplies, small DC motors, solenoids, and -- of course-- optointerrupters in various sizes, shapes, and forms.

Not too long ago, I was building a robotic controller with an old CDROM stepper. I and wanted to have a way to safeguard the very end of the travel path on the lead screw. I used an optointerrupter. I found another optointerrupter and used it on the other end of the lead screw. I wanted one more to show the home/reset position. I dug through all of my printer supplies and found this (depicted above with question mark) little "doo-dad!" It's another optointerrupter, but it's wired a little differently. What the Heck? I found many of these on HP printers. They aren't marked. Most optointerrupters that are shown in diagrams have An "E" for the emitter, and have an "S" for the sensor. HP usually has a small breadboard form-factor with three wire leads extending from the board just like the picture above. Some have been used as rotary encoder sensors.

Fear Not, for I have figured the "little booger" out, and it's just another optointerrupter, just smaller.

This instructable will demonstrate how to use the tiny optointerrupter it to switch an LED on and off.

Supplies

Arduino
salvaged "little booger", optointerrupter
2M Ohm Resistor
180 Ohm Resistor
A Breadboard
330 Ohm Resistor
LED Light
A handful of Male-Male Cables

Step 1: The Wiring Is a Little Different

Understand that this optointerrupter is slightly different.

Once again, a standard optointerrupter will have a simple LED, "E", on one end and a sensor, "S", on the other.

The Standard Optointerrupter

The LED, "E" end, is just like any other LED -- it needs a resistor. I like to use a 220 Ohm resistor on that end of the standard optointerrupter. Most common IR LEDs use lots of amperage-- nearly twice as much as a common white LED. A 180 Ohm resistor is also adequate on a 5v current.

The "S" side (sensor) is hooked up to ground and the arduino data pin to collect the input. To make sure the data pin is not triggered and remaining in the ground state, a leak is created on the arduino side with a 10k Ohm resistor to bring the arduino pin back to "+" (HIGH).

The Tiny Optointerrupter

But wait, The little optointerrupter on the board only has three wires coming from the small indepentent breadboard. ...and it doesn't have any "E" or "S" printed on it. Yes, you can desolder the little optointerrupter from the board-- but you should do this instead.

Look at the first picture in my series of pictures above. This is the easiest way to use the optointerrupter for an arduino. I tried a number of resistors between the collector and arduino and the best performance seems to be with this set of resistors, a Two Mega-Ohm, and a One Hundred-eighty Ohm , on a 5v circuit.

Step 2: Wiring Up

Wire up the Optointerrupter and the LED as shown above. If it's wired correctly, you should be able to see the little infra-red light from the optointerrupter's LED side with a phone camera.