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How to Wire IR Diodes

LEDs are diodes optimized to produce light when they are given a current. Infrared or IR diodes are LEDs especially constructed to produce light in the infrared spectrum. They are usually combined with detectors such as phototransistors, photodiodes or photoresistors. This allows them to be used in electronic devices such as alarms, remote controls and light switches.

To wire an IR diode, place it in series with a current limiting resistor. Test the IR diode by constructing a detector circuit. The detector circuit may be a phototransistor wired in series with a LED.

Things You'll Need

Infrared diode
Phototransistor
2 270-ohm resistors
Green led
2 9 V batteries
2 battery holders
2 solderless breadboards
Jumper wires

Instructions

IR Diode Circuit
- 1
  Connect the battery holder to the breadboard, making sure that the leads are in different columns. Attach one lead of the resistor to the column that the holder's red lead is in, but place its second lead into another column.
- 2
  Place the positive lead of the IR diode into the same column that the resistor's second lead is in. The diode's positive lead is usually indicated with the longest leg. At the same time, insert the diode's negative lead into a separate column.
- 3
  Wire the diode's negative lead to the battery holder's black lead. Do this by inserting a jumper wire between them. Place this circuit to one side.
Phototransistor Circuit
- 4
  Connect the second battery holder to the second breadboard. Again, the leads must not be in the same column.
- 5
  Identify which lead of the phototransistor is the collector, and which is the emitter. Do this by studying its original package, or a data sheet. The collector may be the shorter lead.
- 6
  Attach the phototransistor's collector lead to the red lead of the battery holder. Insert the emitter into a separate column.
- 7
  Add the first lead of the remaining 270-ohm resistor to the emitter column, but insert its second lead into a different location. To this new column, add the positive lead of the green LED. Connect the LED's negative lead to the column that the black battery lead is in.
IR Radiation Detection
- 8
  Place the batteries inside the holders for the two circuits. Check to see that the wires are firmly in place. Use a digital multimeter to measure the voltage across the diode. Do this by placing the red probe on the plus side of the diode, and the black probe on the negative side. Check the voltage across the phototransistor the same way.
- 9
  Carefully lift the IR diode circuit. Tilt it so that it is at an angle.
- 10
  Hold the IR diode circuit so the diode is above the phototransistor. The green led will light.

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