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DIY Infrared Receiver

An infrared receiver may act as a switch or modulator. It receives signals from a source and in response, turns devices on or off, or changes their behavior. One common infrared source-receiver pairing is that of a photo-diode source with a photo-transistor detector. Photo-diodes and photo-transistors are semiconductors constructed to be sensitive to light.

To build a do-it-yourself infrared receiver, connect a photo-transistor to a regular transistor. The transistor's purpose is to amplify the photo-transistor's signal. Add two resistors to the transistor's base, to ensure that it receives the proper voltage. Use a capacitor at the base as well, to prevent DC noise from entering. Control the photo-transistor's sensitivity by placing a resistor at its collector. The infrared source may be a photo-diode, flashlight, lamp or a remote.

Things You'll Need

Phototransistor
2N3904 or 2N222 NPN transistor
Piezo buzzer
0.1 microfarad capacitor
3 4.7k-ohm resistors
1 22k-ohm resistor
1 47k-ohm resistor
10k-ohm resistor or potentiometer
Infrared source
9-volt battery
Battery holder
Breadboard
Jumper wires
Digital multimeter

Instructions

- 1
  Discover which of the transistor's leads are the emitter, base and collector. Determine the collector and emitter leads for the photo-transistor. The information for both may be found from their data sheets or packages.
- 2
  Insert the transistor into the breadboard so that each of its three leads occupies a separate column. Add the 22k resistor so that one end is placed in the column of the collector lead. Use a jumper wire and connect the resistor's other end to one of the holes near the red stripe at the top of the bread board. The red stripe indicates positive voltage. Attach one end of a 4.7k resistor into the same column with the emitter, but place its other end into a separate column. Use a jumper wire to attach this end to one of the holes in the row next to the blue stripe at the top of the bread board. The blue stripe indicates that the row is ground, or zero voltage.
- 3
  Add the second 4.7k resistor to the breadboard so that it is parallel to the transistor, but is a few rows down from it. Add the third 4.7k resistor so that it is also parallel, but put its right end into the same column with the left end of the second resistor. Insert a jumper wire between this shared column and the column with the transistor's base. Attach the left end of the second resistor to ground. Attach the right end of the third resistor to the positive voltage row.
- 4
  Connect the capacitor to the column with the base. Insert the photo-transistor into the breadboard. Attach a wire between its collector lead and the end of the capacitor, so that the photo-transistor is also connected to the base. Set the photo-transistor's emitter to ground.
- 5
  Add the 47k resistor so that it is parallel to the transistor. Attach its right lead to the base and use a jumper wire to attach its left lead to the positive voltage row.
- 6
  Connect the battery holder so that its black lead goes to ground, and its red lead goes to positive voltage. Add the battery to it.
- 7
  Observe the circuit's output with a multimeter. The output is at the transistor's emitter, parallel to the first 4.7k resistor. Place a jumper wire vertically in the emitter's column, and another one into the ground row. Attach the red probe of the multimeter to the wire at the emitter, and its black probe to the wire at ground. Turn the multimeter to a low voltage setting. Point the infrared source at the photo-transistor's viewing angle, and turn it on and off rapidly. The voltage reading will fluctuate.
- 8
  Test the circuit's output with a piezo buzzer. Use a jumper wire to attach one side of a 10k resistor or potentiometer to the transistor's emitter column. Attach the plus side of a buzzer to the resistor's right side. The buzzer's leads must not be in the same column. Attach the left side of the buzzer to the ground row. The buzzer will sound continuously. Point the infrared source at the photo-transistor as before, and switch it on and off. The buzzer's tone will be modulated.

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