The S-meter is a signal strength meter used in communication receivers. This circuit was found in a 303 Circuits from the 90s, European publication.
This circuit was found in a 1987 magazine. It measures monitors the heartbeat through a...
This crystal-controlled circuit was obtained from a 1980s documentation. The power supply should be 5...
This circuit is from 1957 Raytheon documentation. The phone must be high impedance with 600 ohms...