Proximity Detector Circuit Using NE555 PCB

Posted on Feb 6, 2014

This post shares a proximity detector circuit comprising mainly NE555 IC. This circuit can be used for burglar alarms based on beam interruption, with the added advantage that the transmitter and receiver are housed in the same enclosure, avoiding any wiring problems. This proximity detector is constructed using an infrared diode detector. Infrare

Proximity Detector Circuit Using NE555 PCB
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d detector can be used in various equipment such as burglar alarms, touch-free proximity switches for turning on a light, and solenoid controlled valves for operating a water tap. Briefly, the circuit consists of an infrared transmitter and an infrared receiver (such as Siemens SFH506- 38 used in TV sets). The transmitter part consists of two 555 timers (IC1 and IC2) wired in astable mode, as shown in the figure, for driving an infrared LED. A burst output of 38 kHz, modulated at 100 Hz, is required for the infrared detector to sense the transmission; hence the set-up as shown is required. To save power, the duty cycle of the 38kHz astable multivibrator is maintained at 10 per cent. The receiver part has an infrared detector comprising IC 555 (IC3), wired for operation in monostable mode, followed by pnp transistor T1. Upon nreception of infrared signals, the 555 timer (mono) is turned on` and it remains on` as long as the infrared signals are being received. When no more signals are received, the mono goes off` after a few seconds (the delay depends on timing resistor-capacitor combination of R7-C5). The delay obtained using 470kilo-ohm resistor and 4. 7 µF capacitor is about 3 seconds. Unlike an ordinary mono, the capacitor in this mono is allowed to charge only when the reception of the signal has stopped, because of the pnp transistor T1 that shorts the charging capacitor as long as the output from IR receiver module is...

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