LED Outdoor Thermometer

I had a Radio Shack indoor/outdoor thermometer that I used for may years. It finally croaked, and I needed a replacement. I only wanted to know the outdoor temperature. A requirement was that the display be visible night and day without pressing buttons. Another requirement was to eliminate batteries and the nuisance of replacing them. So I designed this one, using a ATmega48 and a 4 digit numeric LED display, powered by a ubiquitous 5V switching wall wart. It uses an LM19 Celsius temperature sensor, but a single line of code could be added to convert to Fahrenheit if desired.

Outdoor thermometer

There's nothing special about this project, the output of the LM19 is sampled by the ATmega48 A/D and the temperature calculated. There is an array for storing a few samples and the display shows the average.

Thermometer Outdoor photo 1Thermometer Outdoor photo 2

The only thing of note is the two buttons at the bottom of the circuit board. The LM19 accuracy is plus/minus 2.5 degrees C. The buttons are used to program in a correction factor. Each press changes the temperatore one tenth of a degree. The left button is down, and the right button is up. The correction factor is stored in flash memory so it is remembered in case of power loss.

Thermometer outdoor schematic
(Click to enlarge)

Download C source code for the thermometer

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