Two-tone solar buzzer (CB20493E)

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

Drill Speed Control (CB1353E)
This simple half-wave control using an SCR, which may be TIC106, has been obtained from a US...
Sine Wave Oscillator Using an Inverter I (CIR097E)
The circuit shown here can be used to produce low-frequency sine wave signals from CMOS logic. The...
Variable Frequency Oscillator (CB4050E)
This VFO was found in a 1980s documentation. The central frequency is given by the crystal and the...