Does anyone know where I can get a cheap temperature sensor with a RS232 output ? I have now moved my server out into my garage as we discussed here a few months ago. All seems to be fine so far, it has been out there for about 8 weeks so far. I am currently using a small cheap max/min thermometer, which tells be the temperature has stayed between 5°C and 21°C. It never appears to vary by more than 10°C over a 24 hour period.

However, I would like a more useful monitoring system, so I have been looking for temperarure sensors that I can plug into the serial port on the server (I want to throw the data at mrtg to give me pretty graphs). The problem is that everything seems to be so expensive as it is aimed at industrial uses. I refuse to pay $150+ for a thermometer ! I don't need this think to be stunningly accurate, I am more interested in changes in the temperature rather than the absolute temperature anyway.

So, does anyone out there know of any cheaper RS232 temperature sensors ?

I would like to measure humidity as well, but the prices for humidty sensors seems to be even worse.

Failing that, does anyone have a schematic for a simple circuit that I could build to provide this functionality ? (if I can remember where I put my soldering iron)