This circuit triggers an alarm in the event of a power failure. The circuit is from an 80's documentation, being powered by 9 V battery. The parts are common today.
This circuit uses PNP transistors that can be BC558, but if the power is reversed, BC548 can be...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...
This circuit was found in the Linear Technology Applications of 1997. The circuit uses components from...