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First published on: 1-12-2005
Automatic Washbasin Tap Controller
Akshay Mathur and Abhay Mathur
Make your washbasin tap work automatically when you put your hands just below the water tap outlet. This infrared-based system detects any interruption of the IR rays by your hands or utensil and water automatically starts flowing out of the tap.
The circuit is built around 555 timers and comprises transmitter and receiver sections. Both the transmitter and the receiver work off 5V DC. The IR rays continuously emitted by the transmitter fall on the receiver. As soon as an obstacle comes in between the receiver and the transmitter, interrupting the IR rays, the output of the IR sensor goes low momentarily to trigger the timer circuit in the receiver and water comes out for eleven seconds through the tap.
The receiver circuit comprises the sensor module, monostable timer and relay driver circuit (see Fig. 2). The sensor module TSOP1738 is sensitive to IR radiation modulated at 38 kHz. Its normally high output goes momentarily low when any IR radiation is detected or interrupted.
The relay driver circuit consists of resistor R8, transistor BC548 (T2) and free-wheeling diode D1. Diode D1 protects the relay from damage by high voltages generated by the back emf when the relay is de-energised.
The time period for which the timer goes high can be calculated as follows:
Ton=1.1 R6C5=1.1×100×103×100×10–6=11 seconds
When you put your hands between the IR LED and IR sensor, the relay energises to make the solenoid open up the valve and water flows out of the tap.
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