Smoke-detector

  
This smoke detector uses a MEM 817 p-channel enhancement mode MOSFET as its buffer amplifier. Operation of the sensor is based on a decrease in the current when smoke enters the chamber, thereby causing a negative voltage excursion at the gate of the buffer MOSFET.
Smoke-detector - schematic

Quiescent voltage values at the output of the chamber vary from about -4 V to -6 V, and detection of smoke will result in an excursion of about -4 V. The MOSFET is connected as a source follower.




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