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Infrared Toggle Switch for Home
Appliances
Introduction Modern IR
remote controls generate modulated pulse train
of 38KHz frequency when any key on the remote is
pressed. With the use of capacitive filtering we
will convert the stream of pulses into one pulse
regardless of the key entered. This way, we will
be able to toggle a relay switch with any key
pressed on the remote. This project has been
tested with varieties of IR remote control
devices like that for TV, DVD, digital camera,
etc., and it worked well.
Circuit Diagramm
The TSOP 1738 IR
receiver module detects the 38KHz input pulses
received from the IR remote control device. Under
stand-by condition, the output pin of the IR module
is at logic High, and when it detects the train of
pulses, they appear at its output. The output from
IR receiver is fed to a PNP transistor (BC557) with
a series base resistor of 4.7K. At the collector of
the NPN transistor, the train of pulses will be
inverted. There is a 10uF capacitor and 100K
resistor connected from the collector to ground. The
function of capacitor is to convert the train of
pulses into a single pulse, and the resistor is to
provide the discharge path for the capacitor.
So lets see what happens when a key on the
remote is pressed. During standby, the output of IR receiver module
is High, so BC557 is cut off. The capacitor is fully discharged, and
the collector of BC557 is at ground. When a key is pressed on the
remote, the train of pulses arrived at the base of BC557 turns it ON
and OFF very fast. When it is ON, the capacitor gets charged through
the collector current of BC557, and when it is OFF, the capacitor
starts to discharge
through 100K resistor. But the train of
pulses is so fast (38000 pulses per second) that the capacitor
doesn't get chance to discharge. So, the bottom line is, every time
a key is pressed from the IR remote, a positive going clock pulse is
generated at the collector of BC557 transistor.
Next comes CD4017, a decade counter. It counts
low-to-high going pulses up to 10 that are arrived at its CLK pin
(14) and pulls the corresponding output (Q0-Q9) High. When it is
just turned on, Q0 goes High, and when it gets a first low-to-high
pulse (when a key is pressed from the IR remote) at CLK i/p, Q0 goes
Low and Q1 goes High. Q1 output is connected to a LED through a
current limiting resistor to indicate the ON/OFF status. The Q1
output is also used to drive a relay switch through a NPN transistor
(BC547). I used 5V DC relay that requires about 70mA current from 5V
source to turn ON. This current is provided by BC547.
Complete
circuit before putting inside the box
Packing
inside a box for safety as it deals with 120V
AC.
Now, lets see what happens when a
key is pressed again. The counter advances by 1, Q1 goes Low (relay
is OFF), and Q2 goes High. If we connect Q2 to Reset input of
CD4017, the counter is going back to the initial condition (Q0 High,
Q1 and all others Low), and is ready to get another key press signal
to turn the relay ON. This way the switch is toggled every time a
key is pressed from the remote.
Power Supply
The power supply for the circuit
is provided through a 5V regulator IC LM7805. A 12V
step-down transformer with a bridge rectifier and a
capacitor filter provides an unregulated DC input to
LM7805. The regulator IC provides a constant 5V
supply for the circuit. Be
careful on the output side of the relay that connects to 120V AC
line. A reversed biased
diode parallel to the relay input is for back emf protection.
Switch in
Operation
Download
yahoo.com
The
infra-red (IR) toggle switch project described
here is aimed to provide control mechanism for
electrical appliances that do not have remote
operation features. The goal is to construct a
black box where you can plug-in your 120V AC
appliance and control ON and OFF operations with
any modern IR remote control devices.
Below are some snapshots showing the IR toggle
switch in operation
Device OFF
Device ON
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