With this circuit it is possible to measure RF signals with a common multimeter. Signals up to 200 MHz can be detected. The diode supports general-purpose equivalents.
The circuit is from the 1994 National Semiconductor Linear Applications Handbook. The component used is...
This circuit, which is present in other points of this website, was found in a 90s Hands On...
This simple circuit produces a tone when triggered by any vibration picked up by the sensor. The...