Diagram for Reference

A very simple Ionization Smoke Detector with Interconnect and Timer alarm circuit can be constructed using the A5367 low-current, CMOS circuit that provides all of the required features for an ionization-type smoke detector. A very nice thing at this ionization smoke detector circuit CMOS ic manufactured by Allegro MicroSystems is the interconnection features , which allows as many as 125 units to be interconnected so that if any unit senses smoke all units will sound their alarm. In addition, special features are incorporated to facilitate alignment and test of the finished smoke detector.

This detector needs to be powered by a 9 volts DC power supply (or a 9 volts battery ) .Circuit require few external components and is very easy to be configured . As you can see in this diagram , the sound alarm is “produced “ by an piezoelectric element .

Ionization Smoke Detector Circuit Diagram

Use an external resistor in point A to adjust sensitivity for a particular smoke chamber. Select resistor from point B is to reduce sensitivity during Timer mode.A resistor to VSS or VDD may be added to point C pin to modify low battery voltage threshold. Value of components marked with D will vary, based on the piezoelectric horn used.

An internal timer is provided that can be used in various configurations to allow a period of reduced smoke detector sensitivity, referred to as Timer (or Hush) mode. Internal test circuitry allows low battery check by holding the FEEDBACK and OSC CAP pins low during power-up, then reducing VDD and monitoring the HORN1 pin

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