This temperature may look like several dozens thermostats that measure temperature and performs some action (switches relay) when temperature threshold is reached. Actually this is what this one does - it activates a relay with fan connected when temperature reaches 40ºC.

There is another thing what makes this device little bit different from others - it accepts TV remote control commands. By pressing 1, 2, 3 and 4 buttons each of four relays can be turned ON/OFF manually. Design is based on AT89C51 microcontroller which reads LM35 temperature sensor data via ADC0804 ADC. Compares temperature value to given threshold and in case of alarm it sends relay activation signal via ULN2003 Darlington transistor array chip. Grab project files, build and keep things cool.