Bike speedometer (CB20497E)

This circuit can be powered by a solar cell. The circuit is from a 1991 documentation having a phototransistor as sensor.

Field Strength Meter (CB6539E)
Found on an 80's Elektor, this circuit uses common components, being the diode a general purpose...
Microwave Oscillator (CB21748E)
This 1.6 GHz oscillator with 40 mW of output power was found in a Popular Electronics from...
Audio Oscillator 4049 (CB8794E)
Found in a 90’s Popular Electronics, this circuit uses two CMOS inverters to generate a signal of...