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					                                                                                                                         CIRCUIT IDEAS




INFRARED REMOTE CONTROL TIMER                                                                                    S.C.
                                                                                                                      DWI
                                                                                                                         VED
                                                                                                                            I




                                                                            Fig. 2: IR receiver section
DIPANJAN BHATTACHARJEE                          whose frequency may
                                                be varied with the help


T
        his infrared remote control timer can   of potmeter VR3.
        be used to turn an appliance on/off         When switch S1 of
        for a period of 0.11 second to 110.0    the transmitter is
seconds.                                        pressed, the modu-
    The circuit comprises two sections,         lated IR rays are gen-
namely, the transmitter section and the         erated, which are re-
receiver section.                               ceived by photodiodes
    Fig. 1 shows the IR transmitter sec-        in the receiver section
tion. The astable multivibrator NE555 (IC1)     and amplified by the
is used to generate a 10kHz modulated IR        amplifier circuit. The
signal. The output of IC1 is connected to       output of op-amp goes
the base of pnp transistor T1 via resistor      low to trigger the
R2. Two infrared LEDs (IR1 and IR2) are         monostable. Then high
connected in series between the collector       output at pin 3 of IC3
(via resistor R3) and ground.                   activates the two-
    When switch S1 is pressed, the IR LEDs      changeover relay RL
transmit the modulated IR signal of 10-11       via transistor T3
kHz. This frequency can be changed with         (BC548) for a preset
the help of VR1 potmeter.                       time.
    In the receiver section shown in Fig.           The on/off time
2, two photodiodes (IR3 and IR4) receive        can be set in the timer
the IR signal transmitted by the IR trans-      with the help of VR3
mitter. Transistors T2 and T3 amplify the       and C10. Switch S2 is
weak signal. The amplified signal is fil-       used to reset the
tered by capacitors C6 and C7. The ampli-       monostable. If you
fied and filtered signal is now fed to the      want to turn the appli-
inverting input pin 2 of op-amp IC2 (IC         ance on for a preset
741). The output of IC2 is further con-         time, connect the ap-
nected to trigger pin 2 of timer NE555 (IC3)    pliance via relay RL(a).
that is used as a monostable multivibrator      On the other hand, if
                                                        you want to
                                                        turn the appli-
                                                        ance off for a
                                                        preset time,
                                                        connect the ap-
                                                        pliance via re-
                                                        lay RL(b). The
                                                        timer can be re-
                                                        set by pressing
                                                        reset switch S2.
                                                             The circuit
                                                        works up to 3
                                                        metres without
                                                        using any fo-
                                                        cusing lens.
                                                        However, you
                                                        can increase
                                                        the operating
                                                        range by using
                                                        focusing lens.
                                                             This circuit
                                                        costs around
Fig. 1: IR transmitter section                          Rs 100.

                                                                                                          MAY 2003   ELECTRONICS FOR YOU

				
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