Low battery indicator (CB9133E)

This circuit was found in Maxim's documentation from the 80's. The integrated circuit is from that time, uncommon today.

Transistor Tester (CB10768E)
I found this circuit in a 1992 Electronics Experimenter Handbook. The circuit can be easily...
Timer (CB5018E)
This egg timer has been found in an English magazine that no longer exists in 1982. The...
Overvoltage Switch CA3140 (CB24965E)
This comparator application circuit was obtained from the June 1986 Radio Electronics magazine. The...