This circuit was published in the July 1993 issue of Electronics Now magazine. It uses a sensor from the time and triggers a buzzer with a Sonalert-type oscillator.
This ultra-simple polarity indicator uses common green and red LEDs and can work with 3 to 9 V...
We found this circuit in 1964 General Electric documentation. The circuit works with mechanical...
This circuit was obtained in a technical publication from the 1970s. It fires a diac and thus a...