Diode temperature display

How it works

A 1N4148 diode acts as the temperature-sensitive element. Its forward voltage changes with temperature when its operating current is controlled. The converter and display-driver circuitry turn that voltage into a numeric indication.

The original application places the sensor near a car radiator and derives 5 V with a 7805 regulator. A vehicle electrical system also requires attention to transients, reverse polarity, and regulator heat.

On the bench

Calibrate against at least two known temperatures over the intended range. This experiment is not a replacement for an engine-protection sensor or a certified temperature instrument.

Resources & provenance

Rewritten from the original circuits/msr/r3j19ns_msr002.php page. Component values and historical performance claims have not been independently bench-tested. The circuit figures have had their watermarks removed.