Bike speedometer (CB20497E)

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

Sound level meter (CB8224E)
This circuit with a bargraph scale was found in a 90s Popular Electronics. The circuit measures...
Simple DC Amplifier (CB14028E)
This circuit with only one transistor was obtained in an old English documentation and can be...
AM Transmitter (CB16543E)
This small transmitter that we found in a 1988 documentation, has a range that depends on the...