This 1965 circuit uses a Philips 4068 tube to measure extremely small charges. The circuit has as indicator a micro ammeter and the transistors are of the time.
The purpose of this simple configuration, found in old documentation, is to trigger a buzzer if...
The sensor of this circuit is a large surface diode. We believe that a small solar cell can also...
This 3V-only circuit was found in old American documentation, but can be implemented with...