Simple metronome (CB7285E)

Found in Popular Electronics from the 90s, this circuit uses a 2N2646 and a general-purpose transistor like the BC548. The pot can be 470k.

Three-input majority gate (CB7248E)
This interesting logic circuit was found in a manual of neon lamp applications. | Clique na imagem...
Pulsing Tone Alarm (CB4878E)
This variation of the previous circuit produces a pulsating sound when the sensor is activated. The...
Modulated Power Supply For LASER Pointer (CB1184E)
This circuit allows controlling a LASER pointer with an input logic signal. R has 10 ohm for 3 V...