A smoke detector is part of a sophisticated alarm system. Which within the system is a professional, most will include Section detector gas, room filling ions. Or sensitive to radio signals. However, this circuit does not have to be so complicated. Just another 2 LDRs and LED detection.
Only the number of IC LM1801, the circuit helps the device is much less. Designed for this purpose. It consists, in Section controlled by the Zener voltage. Second output reference voltage output, the compare unit. And Transistor output resistance current 500 mA with diode clamp.
Figure 1 the circuit.
This circuit does not require a transformer. Can be connected directly to the home. So there are diode – D1 rectifier as ACV, R2 serves to reduce the voltage at IC1 properly. Capacitor C2 filters the power was smooth. By a Zener diode in the circuit to control the voltage constant.
The principle of this circuit Is The balance of the two LDR. We put both of them in the LDR Bridge system. Any changes. Of resistance. Which is a result of temperature or age of the device has no effect on the circuit.
Another part of Bridget’s is R1, R4 all integrated into the input of the circuit to the junction of R4 and R13. The other input of the circuit by comparing the voltage at circuit point of R2 and R3. The point of the arms of Bridget’s R1 and R12. The circuit in this manner to provide both LDR voltage Bias voltage equal. To work effectively.
In the installation, should install LDR in place that When a gas leak out Light from the LED (D2) is reflected back into the LDR (R13). Makes voltage drop across it down. Resulting circuit SCR Th1 stimulation compared to the current siren horn mouth as P1 to adjust the sensitivity of the circuit.
The hardest thing. To build this circuit are installing the LED and both LDR.In principle, the LED should held between the two LDR. And ensure that no air flowing through the LED and R12 in a small sealed box.
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