Building an Infrared Transmitter for Your PC
By Gabriel Torres on May 9, 2006


Several motherboards have the necessary hardware for the installation of an infrared transmitter/receiver, requiring only the installation of a module containing the infrared sensor. The great problem, however, is that this module is not easily found on the market and, when it is, its price is high. In this tutorial we will show you how to build this module spending barelly nothing. Any user who knows how to use a solder iron can assemble it.

Infrared device

Figure 1: Homemade infrared receiver/transmitter for your PC.

With this module, which was designed by our friend Alain Gailland, you will be able to make the communication among your PC and other devices that have infrared connection - also called IrDA such as palmtops, notebooks and cellular phones. But to do so your motherboard has to have this interface. To know whether or not your motherboard has this interface, you should look for a connector called IR, IRDA, IRCON, SIR, SIRCON or something like that in its manual or in the motherboard itself. This connector usually has 4 or 5 pins and you will need the manual to know the meaning of each pin (+5V, GND, TX and RX), because the function of each pin will vary depending on the motherboard model.

On Figures 2 and 3 we give as an example parts of ASUS A7N8X De Luxe motherboard manual. You will usually find the IR header on the motherboard layout page (Figure 2). We've drawn a red arrow for you to see it. On this motherboard this header was labeled "IR_CON1".

IR Header
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Figure 2: ASUS A7N8X De Luxe motherboard layout. The red arrow indicated the IR header.

The IR header pinout can be found under the "connectors" section of the manual, see Figure 3.Keep in mind that this pinout vary depending on the motherboard, so you need to check on your motherboard manual the correct pinout used on your board.

IR Header Pinout
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Figure 3: Pinout for the IR header on ASUS A7N8X De Luxe motherboard.

The Circuit

You will have to buy two 2N4041 or any general purpose NPN transistor (BC548, for example), a 10 nF capacitor (a.k.a. 0.01 uF), a 4K7 resistor (yellow, purple, red), a 47 K resistor (yellow, purple, orange), a 15K resistor (brown, green, orange), a 22 ohm resistor (red, red, black) and a 1 K resistor (brown, black, red) (all of them 1/8 W or 1/4 W). As for the infrared LED and the infrared photo-diode, use Radio Shack 276-142. All these components can be bought at Radio Shack.

Infrared device schematics

Figure 4: Infrared device schematics.

When assembling the circuit, the only special care you will need is to make the transmitter (LED) and receiver (photo-diode) become perfectly aligned, side by side, as shown in Figure 1.

After assembling the circuit, you will have to connect it to the motherboard IR connector. Notice that we have marked four points in the circuit: Vcc, Gnd, TX and RX. These points should be connected to the corresponding points in the motherboard IR connector.

It is also important that you configure the IR interface to operate in full-duplex mode at the motherboard setup to achieve higher performance.

After the device is connected, it should be automatically recognized by Windows, and it will show an infrared icon on the task bar near the clock (lower right corner). As soon as you approach your cellphone, handheld or notebook infrared sensor to the device you build, Windows will alert you that it found another computer nearby, allowing you to transfer files between the device and your PC.

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