This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based on a 741 that activates a buzzer with oscillator. R5 adjusts the sensitivity.
This well-known configuration, used in many car radios, is from the Philips Data Book of 1990. The...
With this circuit it is possible to expand the voltage range of a common multimeter, also...
This circuit for very long-time intervals was found in the March 1993 Radio Electronics magazine. Times...