Red alert for a frost warning!

This project gives an indication of the outside temperature by the changing appearance of a three-color light-emitting diode (LED). Above a certain threshold (nominally 6 degrees C), it will be off. As the temperature falls, it will progressively appear Green (below 6C), Yellow (below 4C), and Red (below 2C). These operating points could be changed over a small range to suit the application.

The Ice Alert will be found particularly useful by car drivers. However, readers will find many other applications for it. For example, gardeners could use it to monitor the temperature inside a greenhouse or at the ground surface from a point inside the house.