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Les langues disponibles
Optics
Fibroptonic
Ref : 202 012
3 Experiment no. 10
Remote alarm triggered by light
This set-up could serve as an alarm clock sensitive to daylight.
ENGLISH
2.3 Experiment
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When we toggle the receiver's switch to On, the green LED comes on only if we
illuminate the photoresistor sufficiently. An infrared signal passes through the
optical fibre and the red LED also comes on.
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When the phototoresistor is lighted with a pocket torch, the signal received when
viewed on the oscilloscope has on amplitude of 0.3 to 0.6 V for a supply voltage of
6 V.
•
If we light the photoresistor with a pocket torch in an oscillating motion, the green
and red LEDs go on and off alternately. The signal observed on the oscilloscope
is almost periodic.
Various applications
3.1 Equipment:
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Transmitter
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Receiver
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Optical fibre
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6, 9 or 12 V Power supply
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Pocket torch
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Photoresistor module
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LF sine-wave signal generator (amplitude 0.5 V and frequency 1 to 2 kHz).
3.2 Set-up and experiment
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Repeat the set-up of figure 14 by connecting the signal generator to the black and
yellow terminals of the transmitter (black to the ground of the LFG). One of the 2
devices (power supply or LFG) must have a floating ground because of the set-up
on the transmitter side.
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Place the 2 switches on EXT and On (transmitter unit)
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Set the sound level to the maximum (potentiometer of the receiver)
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Illuminate the photoresistor with a pocket torch and the alarm is triggered (the
sound level is greater and the triggering threshold lower if a 12 V DC power supply
is used). The torch can be moved quickly from left to right and right to left alternately
over the photoresistor.
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