Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
Found in an American documentation from the 90s, this sophisticated circuit is suitable for...
This Wheatstone bridge has a thermistor or NTC sensor, allowing the measurement of temperatures by...
This circuit shows how to get 5 V under low current from an operating amplifier 741. I got this...