Practice code oscillator (CB21696E)

In the figure we have an astable multivibrator driving a speaker to produce audio signals for Morse code practice.

Moisture Detector (CB22049E)
We found this sensitive moisture detector in an old documentation. The circuit uses a common JFET,...
Infrared Remote-Control Test (CB18824E)
This circuit, with the assembly in a contact matrix, was found in a publication from the 90s. The...
Darlington Modulator (CB14800E)
This modulator circuit for transmitters was found in American documentation from 1964. It can be...