IrDa transcievers (infrared light transmitter and recievers) are used for wireless comunications for example between cell phones and computers. Normally PCs are bought without without any IrDa transciever; you can buy them as accessories, but they are bulky and expensive. These devices you typically want to occupy no space, but still 'see' your desktop, since sight contact is required for the transmission of data through IrDa. Beyond the tranciever chip with the light emitting diode and the receiving photodiode (an Agilent HDSL 1100, packaged in black plastic with two half sphere IR lenses) only common resistors and capacitors are used, mainly for protecting the chip and signal from voltage spikes. I decided to build one myself, for improving my soldering skills, and get an IrDa as tiny as possible. I implemented the reference scheme from the manual of th IrDa chip (local copies 1, 2).
So let's attach the capacitors and resistors
Same from above (already nearly finished)
Here's the finished product. With the red swich one can swich between the SIR and the faster but at the time not yet so well supported FIR standard. BTW the first time I attached it to my computer one capacitor went up in smoke. Damn the malodour lasted longtime! It was a special capatitor with a polarity. Now I know, and the IrDa is working well.