(N + 1) Wires Connect N Hall-Effect Switches

  
Hall-effect switches have several advantages over mechanically and optically coupled switches.
(N + 1) Wires Connect N Hall-Effect Switches - schematic

Their major drawback is that they require three wires per device. This circuit, however, reduces this wire count to N+1 wires for devices. Amplifier IC1A is configured as a current-to-voltage converter. It senses the sensor assembly"s output current. When the Hall-effect switch is actuated, the sensor"s output current increases to twice its quiescent value. Amplifier IC1B, configured as a comparator, detects this increase. The comparator"s output goes low when the Hall-effect switch turns on. The circuit also contains a fault-detection function. If any sensor output wire is open, its corresponding LED will turn on. If the power-supply line opens, several LEDs will turn on. A short circuit will also turn an LED on. Every time an LED turns on, Ql turns on and the alarm relay is actuated.




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