Smoke detectors are generally used in advanced alarm systems. Most of this professional devices use gas-detectors, ionization rooms or radioactive elements as sensors. In this circuit we are not using any of this complicated components. Instead of these, we are using two LDRs and one LED.
LM1801 special-purpose IC ,which is designed especially for smoke detectors, provides us building this circuit by using the minimum number of components. It includes one internal zener supply, two reference voltage outputs, one voltage comperator, fixing diodes and one 500mA output transistor.
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