pretty much all of which would involve some kind of thermometer, thermistor, thermocouple, or other thermo-adjacent device. But what if you need to measure something really hot, hot enough to ...

[Clovis Fritzen] has given us an ingenious example, in the form of a PCB ruler with a built-in thermometer ... the minimum of components, a thermistor for measurement, and a couple of LEDs ...

The thermistor inside the thermometer detects how much electricity can pass through it. When the temperature rises, the electrical resistance changes. A tiny computer inside the thermometer ...