Practice code oscillator (CB21090E)

Found in Popular Electronics from the 90's, this circuit consists of an audio oscillator for Morse code practice.

S-meter (CB1405E )
The S-meter is signal strength meter, coupled to telecommunications receivers to indicate the...
Operational Connected Optocoupler Shield (CB16018E)
This circuit is suggested by Motorola, making it possible to use an optical coupler of type 4N26...
Dynamic Analyzer (CB12833E)
Dynamic analyzer is another name given to a signal follower or signal chaser. This circuit is from...