Using IR modules from VCRs

1) Intro

Some time ago, I came across the Lirc (Linux Infrared Remote Control) website and decided to build a serial port IR receiver. They had a list of suggested IR receiver modules, but I was unable to buy one, so I had to think of using something else.

A IR Receiver module is usually a photodiode and a 38khz detector. Most of them have 3 pins. VCC, GND, an output pin. If a 38khz carrier is detected, the output pin will become active. Some modules are active low, and others are active high. It is sometimes required to use an inverter(eg: 7404) to get the correct signal.

At first I thought to build a 38khz detector and to use a photodiode for receiving IR, but I soon realized that this would be too much trouble. Instead, I decided to use the IR module from one of my old VHS I had lying around.


2) Finding the module inside the VCR


 		This should be pretty easy. Just remove the plastic cover from the front panel, and you will probably see a small metal cage somewhere, as shown in the picture to the left.


3) Figuring out the pinout

There are 2 types of modules used in VCRs:
  1. Self-contained modules
  2. Built on board modules

1. Self-contained modules

Self contained modules are usually come with their metal cage soldered to the PCB, with 3 wires or pins coming out. Here are pictures of such modules:

The pinout is not usually too difficult to guess. If you're lucky, it will be printed on the pcb like this:

Otherwise, you can find the pinout by trial and error. Simply connect the ground, vcc. Connect the output pin to a led using a high resistor value like 1k. Also, limit the current in the VCC line if possible(using a resistor or a good power supply).

To test your pinout, aim a remote control to your module and press a button. The led will blink if you have the right pinout.

2. Built on board modules

Built on board modules have their metal cage soldered to the PCB, and a bunch of component (sensor, chips, resistor, caps...) directly soldered to the PCB. If you have this type of module, I recommend that you cut the PCB around it using a dremel or something.

Next, look at the board layout. Usually, this area is insulated with a ground plane. You will probably see 3 traces going inside the module like this:

One of them is VCC, another GND, and the last one is the output. You can easily guess which one is the ground and vcc. Just follow them on the PCB, and it will eventually connect to other chips. You can look theese chips datasheet to learn their pinout. If the trace connects to a VCC or GND pin, you got it. The remaining trace is the output.

4) Using the module

You can use these modules as an universal infrared receiver for your computer with projects like Lirc. You build an Infrared Break Beam detector. You can extend the range of your remote controls by building a repeater.

Written by Raphaël Assénat <raph@raphnet.net>, in the hope that it will be useful. Comments and suggestions are welcome.
Sun Sep 29 15:29:17 EDT 2002