Two-tone solar buzzer (CB20493E)

This circuit was found in a 1991 publication. The transistor can be a general-purpose type.

Monostable with Schmitt Trigger (CB15967E)
This circuit serves as the basis for applications such as timers and alarms, being its base two of...
XTAL Short Wave Transmitter (CB14892E)
This transmitter operates in the 80-meter range, around 3.5 MHz, with an exact frequency value...
Touch Relay (CB18273E)
With the circuit shown in the figure, it is possible to connect or disconnect a load controlled by the...