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Description:

This is a single channel (on / off) universal switch that may be used with any Infra Red

remote control using 36-38kHz. (This is a very common remote handset frequency). Inplace of IR1 a TSOP1738 receiver may be used.

Notes

Any "button" of any remote control may be used to work this universal switch. The

button must be pressed for about one and a half seconds (determined by R3 and C2)

before the relay will operate. The circuit will remain in this state (latched) until reset. Toreset, any button is pressed on the remote handset and held for a short duration.

For example, if you were watching TV, you could press and hold any button on the TV

remote to trigger the circuit. In order not to change channel, you could press the button ofthe channel you are watching. You can connect anything to the relay, for example a lamp,

but make sure that the relay contacts can handle the rated voltage and current.

Circuit Operation:IC1 is an Infra Red module. IR modulated pulses are received and buffered by this IC. It

has a standard TTL output, the output with no signal is held high by R1. A replacementfor IR1 is the common TSOP1738 IR reciver. One gate of a CMOS inverter drives LED1

as a visible switching aid. Another gate buffers the signal and applies it to the time

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constant circuit, comprising R3,C2,R4 and D1. C2 charges via R3, and discharges via R4,

D1 prevents quick discharge via the low output impedance of the CMOS buffer. If using

a TSOP1738 then increase R4 to 470k.

The time taken to charge a capacitor is the product of resistance and capacitance, more

commonly known as the RC time constant. At one RC a capacitor will only charge to63% of the supply voltage. It takes 5 RC's for a capacitor to reach 99% charge. In this

circuit the capacitor charge has to reach the logic threshold of the CMOS invertor. As the

power supply is 5 Volts, the input threshold is around 3.6V, which takes about 3RC's orabout 1.5 seconds. Once reached the inventor triggers the 555 timer and operates the flip

flop. A simulation of received pulses, filtering and output pulse is shown below. Note

that this is not from the actual circuit ( in which case the reconstructed pulse would be

high for the duration of the 555 monostable) but only a spice simulation.

The pulses are further buffered and contain "jaggered edges" as shown above. These

edges are produced by the modulated IR data, and have to be removed. This is achieved

using a 555 timer wired as a monostable, IC3, having an output pulse duration R5, C4. A

clean output pulse is produced to activate the bistable latch, IC4. This is a D type flipflop, built with a TTL 7474 series IC and configured as a bistable. Any version of the

7474 may be used, i.e. schottky 74LS74, high speed 74HCT74 etc. The input is applied to

the clock pin, the inverted output fed back to the data input and clear and preset lines are

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tied to ground. For every pulse the relay will operate and latch, the next pulse will turn

off the relay and so on. Note that quick turn on and off of the relay is not possible. The

output pulse is set at about 2.4 seconds. and input delay by R3, C2 set about 1.5 seconds.

Parts List:R1 3k3R2 1k

R3 22k

R4 220k or 470k if using a TSOP1738R5 1M

R6 3k3

B1 12 VD1 1N4148

D2 1N4003

Q1 B109

LED1 CQX35A

IC1 IR1 available from Harrison Electronics or TSOP1838 or similarIC2 4049

IC3 CA555IC4 SN74HCT74 or SN74LS74

IC5 LM7805

Relay 12 Volt coil with changeover contactC1 100u

C2 22u

C3 100nC4 2u2

1. INTRODUCTION TO IR REMOTE CONTROL SYSTEM :

In modern electronics, electronics remote control system is well known system.

Infrared remote control kits available in the market are quite expensive and it some one wishes

to assemble one, their ICs may not be easily available. More over for simple ON-OFF function

such as controlling a lamp or fan we do not need very complex circuit.

The IR remote control circuit using photodiode and phototransistor sensor suffer

from major drawback of being affected by ambient light and a very low range.

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The IR remote control circuit described here can be used for any simple ON-OFF

function. This system has memories application than other remote control system.

The advantage is that this circuit is absolutely free form ambient lightinterference and provides control range of any to focusing lens.

The components use in this system is in so convenient manner thatwhole assemble is easier to built. This reduce complex city of the system

The advantage of this circuit lies in the fact that it can easily be converted into a

multichannel remote control system. The system comprise two unit transmitter, Receiver Both

transmitter and receiver can be assembled on a general purpose PCB.

Transmitter section consist of power supply, on oscillator and in output stage

including IR LEDS in the transmitter section IC 555 is wired as an a stable multivibrator with a

Centre frequency of about 36 KHZ. The transmitter is powered from a GP 22 size gv. battery.

The receiver uses IR sensor module which is commonly used in colour T.V. for

sening IR Singal from transmitter section. The IR singal from the transmitter sensed by sensor

and its output at pin and goes low which is in turn switch on transistor T1 (BC 557)

consequently capacitors start charging through resister R5, when voltage across capacitor C8

reaches about 3.5V IC 2 (Decade counter 4017) receive a clock pulse at pin 14 and its output at

pin 2 goes high. This result in forward biasing of transistor to (be 148) which energies a really

connected at its collector.

The output of IC 2 (pin 2) is also used for lighting LED, indicating presence of singal for thiscircutary 12 v-0-12v 25 mA transformer is used for supplying the power & IC 7805 is used for 5

v regulation purpose at its output. This regulated 5 v output is given to receiver section

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In the transmitter section ICI (555) is wired as a stable multi-vibrator with a

center frequency of about 36 KHZ. When switch SI is pressed, the circuit gets energized. Output

of ICI is a square wave. The two infrared LEDS connected at its output transmit IR beams

modulated at the same frequency (36 KHZ). The oscillator frequency can be shifted slightly by

adjusting preset VRI.

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The receiver uses an infrared sensor module which is commonly used in colour

television for sensing the IR signals from the transmitter section. The sensor module shown is

figure incorporates a detector diode, an SMD ( surface mounted device) IC which consists of a

band pass filter, an amplifier and a demodulator on a small PCB placed inside a small tin cube

enclosure to get rid of unwanted electromagnetic interference.

When switch S 1 on the transmitter is pressed, the IR LEDs radiate IR beams

with a modulating frequency of 36 KHZ. It may be noted that the IR LEDS are directly driven by

the 555 timer output, and no series current limiting resistor is used with them. This is because at

the high operating frequency, the internal resistance of the battery and the independence offered

by the wires and components leads are enough to keep the average LED current within its

specifications.

The IR signal from the transmitter is sensed by the sensor and its output at pin 2

goes low. This in turn switches on transistor T1, consequently capacitor C8 start charging through

register R5.

When voltage across capacitor C8 reaches about 3.5 V IC2 receives a clock pulse

at pin 14 and its output at pin 2 goes high. This results in forward basing of transistor T2, which

on conduction energises relay RLI connected at its collector. The output of IC 2 (pin 2) is also

used for lighting LED1, indicating presence of signal.

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