We found this circuit in a 1957 Raytheon transistor publication. The circuit can be assembled with more modern transistors with minor changes. The handset must be high impedance magnetic.
This sensor works as an electronic push button, activating a power relay. The circuit must be...
This circuit is based on an old operational amplifier, having been found in documentation from the...
Found in a Maxim documentation, this 1980s circuit drives 4 LEDs on a bar scale. The circuit does...