Two-tone solar buzzer (CB20493E)

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

Flyback Tester (CB23812E)
This circuit appeared in a Radio Electronics magazine in March 1962. The circuit uses two...
Light detector (CB8788E)
Using an LDR as a sensor, this circuit from a 90s Hands-On Electronics triggers a relay in the...
12V To 6 or 9V Reducer For Car (CB4441E)
This simple reducer can supply devices that require currents up to 1 A. The power transistor must be...