This well-known circuit version of the siren was obtained in a Colectro Handbook from the 70s. The transistors are of general use, with Q2 being a BD136 for greater power with power from 6 to 12 V.
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
Suggested by National Semiconductor, this circuit can be applied to almost any operational...
This circuit was found in Radio Electronics from the 90s. The circuit can generate signals up to...