2: Pin configurations of TSOP1738, IR LED and BC547 To prevent unwanted reflection of the IR beam, the finished unit should be mounted such that it does not face a nearby wall.įig. Finally, fit the standby indicator LED1 inside a suitable LED holder such that it slightly protrudes from the front panel. Fit the time-control potentiometer (VR2) in an appropriate position. The dome-shaped face of the TSOP1738 should stick out from the front panel. Fit IR LED1 with a reflecting hood at a recessed position on the front panel of the enclosure. Assemble the circuit on a general-purpose PCB and enclose in a small plastic cabinet. 2 shows the pin configurations of TSOP1738, IR LED1 and transistor BC547. The circuit works off regulated 5V DC.įig. AC mains supply to the load to be switched-on is routed through the pole and normally-opened contacts of RL1 as shown in the diagram. LED1 enables you to locate the switch in the dark. This turns off the standby indicator (LED1) and transistor T1 conducts to drive the 5V relay (RL1). This, in turn, triggers the monostable wired around IC2 and its output pin 3 goes high for a period determined by the 2.2-mega-ohm potentiometer and capacitor C5. When a short IR burst is received by IRX1 (as you wave your hand in front of the switch), the demodulated pulses are fed to the trigger input (pin 2) of the second LMC555 (IC2). Everything required for IR signal processing, including the PIN diode and preamplifier, are assembled on a lead frame and the epoxy package is designed as an IR filter. The TSOP1738 is an integrated miniaturised receiver for infrared remote control systems. The receiver section is built around IR receiver module TSOP1738 (IRX1), timer LMC555 (IC2) and a few discrete components. A 220-ohm series resistor (R3) ensures that the current consumption of the IR transmitter is not out of arrangement.įig. This frequency can be tuned using a 10-kilo-ohm preset (VR1). The multivibrator produces 38kHz pulses (at low duty cycle) that drive an infrared LED (LED1). The IR transmitter is built around timer LMC555 (IC1), which is wired as an astable multivibrator. It has two sections: transmitter and receiver. 1 shows the circuit of the touch free timer switch. A 220-ohm series resistor (R3) ensures that the current consumption of the IR transmitter is not out of arrangementģ.6 IMPORTANCE AND FUNCTION OF THE MAJOR COMPONENTS USED IN THIS CIRCUITįig. The system has two sections: transmitter and receiver. This is achieved by detecting the infrared light reflected by your hand onto a receiver device. The simple touch free timer switch circuit presented here can be operated by moving your hand in front of it. For example, we commonly see use of infrared proximity sensors on public drinking fountains and in public washrooms. This type of infrared proximity circuit is widely used as an electric switch where physical contact is not desired for hygiene purpose.
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