Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

a Photodiode Amplifier with Trigger (CB4579E)
In the figure we have a sensor circuit that makes use of common transistors and a photo diode as...
Diode Coupled Multivibrator (CB19521E)
This unusual configuration, but which has already been explored in other articles, uses diodes in the...
Proximity Switch 567 (CB15008E)
This circuit uses a modulated signal from a PLL 567 to operate safely with an infrared emitter. The...