Damjan Lapuh wrote:
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Does anybody know how many mA I can squeeze from serial port?

Damjan, rephrase the question to: how few mA... :o)

I have recently done a project which also needed supplying through the serial port. I used both RTS and DTR lines as power supply.

From the port of a desktop PC you can get a good few milliamps, perhaps 7.5 for each line. This is because these ports are most usually made with drivers that are fed directly with the PC's +/- 12V. A laptop however is a different story, because these use a MAX 232 type of driver, often of a 3V variety. If you are planning on using 5V devices in your device, expect no more than about 2 mA per line.

My device has a 3V supply voltage. I used an 89C2051, running at 3.68 MHz and built the RS-232 level converter with discrete components to get the lowest possible power consumption. It can be done, but you really need to pay a lot of careful attention to your design.

Best regards,
Rob.