Two-tone solar buzzer (CB20493E)

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

MW Receiver ZN414 (CB4547E)
This circuit was obtained from an English magazine from 1985. The N414 is a complete, not easy to...
Simple photometer (CB20507E)
This 3-component circuit uses an analog indicator. We found it in an old publication....
Relaxation with Operational Amplifier (CB25325E)
The figure shows the basic circuit of a relaxation oscillator with operational amplifier. The...