This filter was found in an American publication from the 1980s. The circuit can be implemented with any operational amplifier. The power supply must be symmetrical.
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...