In this article we discus a simple IC 555 based proximity detector circuit which can be used for detecting human trespassing from a distance.
An infrared proximity detector can be considered as one of the most valuable and widely used circuits in electronic automation application range.
We can typically see it being used in automatic water dispensers, automatic hand dryer units and some specific variants may be witnessed in the automatic doors of department stores.
Working principle of the proposed proximity detector circuit using IC 555
In the design a generation of rapid bursts of peak voltage pulses from the IC LM555 is implemented at a relatively lower frequency rate, which is transmitted via the infrared LED as jets of IR beams.
These transmitted pulses are focused toward the area which is required to be monitored, and is reflected back when a subject or intruder is detected over a phototransistor diode positioned strategically for receiving these reflected signals..
Once this happens the received signals go through processing in order to enable an attached relay mechanism and subsequently an alarm device to get activated.
To test the above implementation an object may be introduced across the zone of the IR beams and the response may be checked by monitoring the relay operation, such as by moving hand in the focused area, within a distance of about 1 meter.
When the reflected signals hit the phototransistor, it develops a potential difference across the 1M pot (adjustable) and triggers the associated Darlington stage, which in turn activate the right hand side 555 stage configured as a monostable circuit.
The relay gets activated in response to this and stays ON depending on the monostable predetermined time delay set by the 1M and the 10uF capacitor.
Parts List fro the proposed IC 555 based IR proximity detector circuit.
2 IC LM 555
2 IC sockets 8 pin
1 relay 12 V 5 pin
1 Infrared Phototransistor General Purpose
1 Infrared Diode General Purpose
2 capacitors. 10 uF / 50 V
1 1N4148 diode
1 red led 5mm
1 68 H
1 470 R H All 1/2 W
1 10k 1/4 w resistor to be connected in between 1M preset center lead and the BC547 pair