Code Sidetone Generator (CB26323E)

This code practice circuit was found in a 1990s issue of Radio Amaterur Today magazine. It produces an audio tone with the 555.

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Electronic Roulette (CB6362E)
This circuit that draws 1 out of 8 LEDs was found in an 80's American documentation. The circuit...
Current relay (CB22522E)
This protective circuit for power lines was found in a Radio Electronics from November 1957. The...
Precision current drains (CB15421E)
In figures 1 and 2 we have two current drains that can be made with operational amplifiers and...