Two-tone solar buzzer (CB20493E)

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

Who is the Fastest? (CB203E)
Only one LED is turned on when S1 and S2 are pressed. The LED that will be on is just the...
Stereo FM Transmitter (CB8459E)
This circuit was found in a 90s Radio Electronics. The FM encoder or multiplexer is an uncommon...
6 or 12 V x 3 A Power Supply (CB1189E)
This source whose voltage depends only on the zener diode used, can supply currents up to about 3 A....