Here is a tiny DS1621 based PC thermometer using PC’s RS232 port for transferring data and getting the power. It displays the measured temperature on the taskbar. It plugs in any free PC com port.
The measurement range of DS1621 is wide; -20 °C to +125 °C with a resolution of 0.5 °C. It can also use the Fahrenheit scale.
The software allows data logging. You can set the sampling rate at 1 reading per 1,5,30 or 60 seconds.
The software supports up to 8 DS1621 temperature sensors.
The circuit uses the com port power by regulating the voltage with LM2936Z-5.0 regulator. So no external power supply is needed.
The circuit is easy to build an includes no programmable device such as a microcontroller. There is no calibration process you have to apply.
DS1621 uses the I2C protocol for communication. The project page provides detailed information about the data transfer, PC software and construction. PCBs for both SMD type and thru-hole parts are available.