Found in the May 1971 Radio Electronics magazine, this is the circuit for a commercial high-impedance instrument. The circuit uses 4 transistors and is powered by 2 9 V batteries.
This 1980s documentation circuit uses a 741 in a different high-speed comparator configuration. The feed...
This circuit activates a relay with a frequency signal determined by the adjustment components. The...
This simple circuit, based on an astounding 555, was found in a 2001 documentation. The circuit...