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Infrared modulated barrier: receiver

Infrared modulated barrier: receiver

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■ What is it for?
Second part: the receiver. It is responsible for capturing the radiation of the transmitter and processing it. When the harness is cut, the relay takes off and controls a gong, a bell or an alarm ...

■ The schema
Some transistors and an integrated circuit, the radiation of the emitter is picked up by the diode D1. T1 and T2 amplify the signal. The value of the connection capacitors makes it possible to efficiently filter the undulations at 100 Hz due to the infrared emission of the incandescent lamps. T3 ground the input 2 of a monostable and, by T4, discharges the capacitor C4. This association constitutes a missing pulse detector. Our receiver therefore receives a train of pulses; As soon as a pulse is missing, the timer gives a signal. It is transmitted to the relay REL by the transistor T5, the direct connection of a relay to the 555. This relay is glued permanently and takes off at break, in the event of power failure or if the wire connecting it to the relay The alarm is disconnected. The time constant chosen for the timer is slightly longer than the period of the pulses. The relay is powered in 12 V, the installation in 5 V, with filtering by an integrated 5 V regulator.

No adjustment is necessary, the usual precautions regarding the orientation of the components are to be taken. The regulator integrated circuit is installed on the metal face to the outside. The relay can cut 8A at 20 A. The installation of the receiver requires some precautions. The diode must not be placed in the sun to avoid saturation, nor will the diode be protected against rainfall, which may reduce the range and, as a limit, attenuate the signal received and cause a command. Radiation protection does not apply to the transmitter. An increase in range can be achieved by installing a lens in front of the receiving diode.
Since the emitting diode is directive, the transmitter must be directed carefully to the receiver.

Nomenclature of components
Resistors 1 / 4W5%
R1: 100kr R2: 1.5Mr R3: R6: 47kr R4: 22kr R5: 1.5Mr R7: 10kr R8: 1.5Mr R9: 6.8kr
C1, C3: 2.2 nF ceramic
C4: 47 nF MKT 5 mm
C5: 220 mF radial chemical 6.3 V
C2: 10 mF chemical radial 16V
Ci 1: integrated circuit TLC 555 or NE 555
CI2: integrated circuit 78 (L or M) 05
T1, T2, T3, T5: NPN transistor BC548
T4: PNP transistor BC 308
D1: diode BP104
D2: silicon diode 1N 4148
Relay REL

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