Based on a 555, this 80's American documentation circuit detects the voltage of a battery and can then disconnect the charger. The transistor may be a general purpose type.
The resistors R determine the frequencies of the oscillator together with C. The circuit is from a...
This configuration can be implemented with equivalent operations. The circuit is from the 1990...
This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates...