The integrated circuit used is uncommon today. The circuit was obtained in the Philips integrated circuits manual of 1990. The reference voltage-range is from 0.5 to 9.0 V.
This circuit is from a July 1970 Radio Electronics magazine. The sensors are metal probes. The 18 V...
This commercial medium and short-wave radio was manufactured in Japan in the 60s. The circuit has...
General Electric suggests this circuit in an 80's documentation. The circuit makes use of PUTs...