Found in American documentation from the 90s, this circuit triggers a buzzer with a Sonalert-type oscillator when the temperature of the sensor reaches a certain value set in R2.
I found this circuit in an English magazine from July 1982. The circuit is still viable because all...
In this version from the 60s, the indicator is a light bulb, but the circuit can be modernized with the...
This crystal-controlled circuit with 60 mW output power is in the Radio Electronics magazine of...