A very simple Ionization Smoke Detector with Interconnect and Timer alarm circuit can be constructed using the A5367 is 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.
The internal oscillator and timing circuitry keep standby power to a minimum by powering down the device for 1.66 seconds and sensing for smoke for only 10 ms. Every 24 on-off cycles, a check is made for a low battery condition. By substituting other types of sensors or a switch for the ionization detector, this very-low–power device can be used in numerous other battery-operated safety/security applications.
This ionization smoke 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 .
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.