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Photodiode Alarm(NE555)

2016-02-20 11:06  
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This article briefly describes the Photodiode Alarm (NE555). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, you can better grasp this principle. In this circuit, you can learn about and purchase these components: NE555.

This Photodiode based Alarm can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered. The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1.

TheNPNtransistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

Figure:1 Photo-Diode Alarm Circuit

Figure 1 Photo-Diode Alarm Circuit

Figure:1 IR Transmitter Circuit

Figure 2 IR Transmitter Circuit

A simple IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IRLEDs are enclosed in black tubes.

 

 


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