This circuit was found in an English documentation from the 90s. It uses a PLL CMOS 4046 and is powered by a 9 V battery. The sensors are two electrodes that must be held by the person.
This circuit was found in an American publication from the 1980s. The circuit generates pulses from...
This circuit is from 1977 Radio Shack documentation. The frequency depends on the capacitor. The...
Found in a 1993 Electronics Experimenter Handbook, this circuit uses a multimeter to measure...