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IR Beam Breaker(LM311)

2017-08-11 00:57  
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This article briefly describes the IR Beam Breaker (LM311). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, can be more effective to grasp this principle. Do you know the circuit, for example, can understand and buy these components: LM311 .

This is an Infrared beam breaking alarm ideal to use in entry or passages.It is based on the working of the popular IR sensor ModuleTSOP1738 which senses 38 kHz Infrared pulses from the IRLEDof the transmitter. Range of the circuit is about 5 meters if the transmitter and receiver are properly aligned

TSOP1738 IR sensor module responds to only 38kHz pulsed infrared rays. It will not sense continuous IR ray from the IRLED.So a transmitter circuit(as one in TV remote handset) based on 555 IC is required. Any standard transmitter circuit based on 555 IC can be used. But its output should be 38kHz exactly.TSOP1738 gives 5 volt output and 5mA current in the off position.

That is when IR rays are not available.Its output is current sinking so that when it receives 38kHz IR rays, output becomes zero.Pin 2 of the module should get a supply voltage between 4.5 to 6 volts.Higher voltage above 6 volts will destroy the device. The module is generally immune to ambient light, but may responds to sources of noice such as electronic ballasts.Figure:1 Circuit diagram

Figure 1 Circuit diagram

Out put from the IR module is given to the inverting input of IC1. LM311 is a precision voltage comparator . It looks like the common Op Amps like LM741, CA3130,CA 3140,TL071 etc.But its pin connections and output are different from other Op Amps.

Pin 2 Non inverting
Pin3 Inverting
Pin 1 Ground
Pin8 Vcc
Pin7 Current sinking Output

Figure:1 LM311 pinouts

Figure 2 LM311 pinouts

The non inverting input of IC1 is connected to a potential divider comprising R1 and R2. When the IR sensor gets IR pulses from the transmitter, output of IC1 remains high. When the IR beam breaks, output from the sensor becomes high which triggers IC1. It then sinks current to activate buzzer andLED.



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