Swith For diagram

This smoke detector circuit diagram is based on the SD2 CMOS Photo-Electric Smoke Detector Integrated Circuit manufactured by Supertex INC and include almost all needed components to build a very simple and high efficiency smoke detector project .As you can see , this smoke detector circuit diagram is very simple an require few external components .

SD2 Smoke Detector Circuit diagram
The LED predriver output pulses an ex­ternal transistor which in turn, switches on the infrared light emitting diode at a very low duty cycle. The desired IR LED pulse period is determined by the value of the externai timing resistor. The Smoke Sensitivity is adjustable through a trimmer resistor which varies the IR LED puise width. The light sensing element is a silicon photovoltaic cell which is held at near zero bias to minimize leakage currents. The circuit can detect signals as low as 1 mV and generate an alarm. The IR LED pulse repetition rate increases when smoke is detected. The IR diode can be RCA Type SG 1010A or Spectronics Type SE 5455-4 Clairex and the IR Photo detector can be Vactec VTS4085 .

Because the SD2 CMOS Photo-Electric Smoke Detector IC is designed for use in low power, battery operated, consumer applications it needs a 9 volts DC power supply (or a 9 volts battery ).