Obtained from a 1969 documentation, this circuit can operate at frequencies up to 500 Hz, counting up to 999. The circuit makes use of neon lamps of the time.
Found in Radio Electronics, this simple indicator circuit uses general-purpose transistors common today....
We found this circuit in an old publication from Argentina. The relay must be of the sensitive type,...
Suggested by Texas Instruments in 1980s documentation, this circuit uses a component of the era....