This circuit is from an August 1984 Radio Electronics magazine. It monitors the state of a RAM backup battery. Resistor R1 determines the battery charge.
This circuit is from 1987 documentation. The operating system used is not common today, but two...
This transmitter for modulated infrared remote control was found in documentation from the 90s....
This commercial receiver was sold in the 1960s in Japan. It is a 6-transistor superheterodyne...