Simple infrared receiver circuit (SIRC) for the PC serial port
The simplest circuit for infrared reception connects the output of the infrared receiver directly to a certain pin of the serial port. That means that the PC has to decode whatever is received, mainly by counting the elapsed time between signal edges.
One of the most well known circuits is the one described in the project LIRC. However, it is possible that, as mentioned in the project page, on some computers (mainly laptops) it might not work well because of its excessive simplicity. Apart from the advanced circuit suggested there, and after looking around to some of the commercial equivalents (PB Fast Media, Animax), the solution for that problem relies on adding a transistor so that the voltage levels that are seen from the PC are correct according to the RS-232 standard.
Power is obtained from the serial port itself, with the supply current coming from both RTS and DTR lines. For the sake of simplicity, an integrated linear regulator (78L05) is used to obtain the supply voltage of 5 volts, but a zener diode with its adecuated regulation resistor could be used as well. Another more modern infrared receiver could be used too.
To use this type of hardware with the PCRC software, it is enough to select under origin for the serial port settings the option SIRC. Since the decoding of the signal is done by software, it is possible that if the computer's CPU gets busy, some signal edges are undetected and certain commands pass without being recognized.
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