The document describes a circuit designed to control home appliances using radio frequency (RF) communication from a remote location. The circuit uses an RF transmitter and receiver operating at 434 MHz to transmit encoded signals from up to 100 meters away. An encoder converts parallel input signals to serial data for transmission, and a decoder at the receiver converts the signals back to parallel to control up to four relays and appliances. The circuit provides a low-cost way to wirelessly control appliances like lights and fans using RF signals.

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PRODUCT DEVELOPMENT LABORATORY II
PRODUCT: HOME APPLIANCES CONTROL USING RF COMMUNICATION
OBJECTIVE: To design an analog circuit that can control home appliances using a remote
based on Radio Frequency Communication.
FEATURES:
 Circuit has been designed without using a microcontroller development board and hence
cost efficient.
 The appliances can be controlled from 100 meters range. Further range can be extended to
a larger distance by increasing the height of antenna.
 User friendly (to understand the control/working and its applications).
COMPONENTS USED
Sl No. Component Specification
(Tx‐Transmitter Rx‐Receiver)
Quantity Approx. Price
(in Rs.)
01 Encoder HT12E (Tx) 01 60
02 Decoder HT12D (Rx) 01 60
03 RF module (ASK) RF Transmitter (Tx) (434 MHz) 01 110
04 RF module (ASK) RF Receiver (Rx) (434 MHz) 01 110
05 Relays 12V Relay SPDT (Rx) 04 80
06 Relay Driver ULN2003 (Rx) 01 20
07 Switches Push Button Switches (Tx) 05 25
08 Resistors 1M, 330R, 33K, 220R (Tx + Rx) 01
(220R‐4)
15
09 Diode LED (Green and Red) (Tx + Rx) Green‐4
Red‐2
20
10 IC Base IC Base (Tx + Rx) 05 30
11 Connectors Female Connectors (4 pins) 03 09
12 Connecting wires Jumper wires (F/M‐F) (Tx + Rx) Bunch 5 per piece
13 Antenna Can be made using connecting
wires (Tx + Rx)
14 Load Bulbs, Fan ( Motor) etc. (Rx) 04
15 PCB Vero Board (PCB 4*4, 2*3) 02 80(Total 700)

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BLOCK DIAGRAM
Output of the decoder is connected to the relay driver which is then fed to relays that
control the loads.

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COMPONENTS DESCRIPTION
HT12E
The 212
encoders are a series of CMOS LSIs for remote control system
applications. They are capable of encoding information which consists of
N address bits and 12‐N data bits. Each address/data input can be set to
one of the two logic states. The programmed addresses/data are
transmitted together with the header bits via an RF or an infrared
transmission medium upon receipt of a trigger signal. The capability to
select a TE trigger on the HT12E further enhances the application
flexibility of the 212
series of encoders.
Features
‐ Operating voltage ‐ 2.4V‐12V for the HT12E.
‐ Low power and high noise immunity CMOS technology.
‐ Low standby current: 0.1 uA (typ.) at VDD = 5V.
‐ Four words transmission for the HT12E.
‐ Built‐in oscillator needs only 5% resistor.
‐ Data code has positive polarity.
‐ Minimal external components.
‐ Pair with Holtek’s 212
series of decoders.
‐ 18‐pin DIP, 20‐pin SOP package.
HT12D
The 212
decoders are a series of CMOS LSIs for remote control system
applications. They are paired with Holtek’s 212
series of encoders (refer to
the encoder/decoder cross reference table). For proper operation, a pair
of encoder/decoder with the same number of addresses and data format
should be chosen. The decoders receive serial addresses and data from a
programmed 212
series of encoders that are transmitted by a carrier using
an RF or an IR transmission medium. They compare the serial input data
three times continuously with their local addresses. If no error or
unmatched codes are found, the input data codes are decoded and then
transferred to the output pins. The VT pin also goes high to indicate a valid
transmission. The 212
series of decoders are capable of decoding
informations that consist of N bits of address and 12‐N bits of data. Of this
series, the HT12D is arranged to provide 8 address bits and 4 data bits.
Features
‐ Operating voltage: 2.4V~12V.
‐ Low power and high noise immunity CMOS technology.
‐ Low standby current.
‐ Capable of decoding 12 bits of information.
‐ Binary address setting.

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‐ Received codes are checked 3 times.
‐ Address/Data number combination.
‐ HT12D: 8 address bits and 4 data bits.
‐ Built‐in oscillator needs only 5% resistor.
‐ Valid transmission indicator.
‐ Easy interface with an RF or an infrared transmission medium.
‐ Minimal external components.
‐ Pair with Holtek’s 212
series of encoders.
‐ 18‐pin DIP, 20‐pin SOP package.
RF ASK Module (434 MHz)
The RF module, as the name suggests, operates at Radio Frequency. The
corresponding frequency range varies between 30 kHz & 300 GHz. In this
RF system, the digital data is represented as variations in the amplitude
of carrier wave. This kind of modulation is known as Amplitude Shift
Keying (ASK).
Why RF is preferred over IR?
Transmission through RF is better than IR (infrared) because of many
reasons.
‐ Firstly, signals through RF can travel through larger distances making
it suitable for long range applications.
‐ Also, while IR mostly operates in line‐of‐sight mode, RF signals can
travel even when there is an obstruction between transmitter &
receiver.
‐ Next, RF transmission is more strong and reliable than IR
transmission.
‐ RF communication uses a specific frequency unlike IR signals which
are affected by other IR emitting sources.
This RF module comprises of an RF Transmitter and an RF Receiver. The
transmitter/receiver (Tx/Rx) pair operates at a frequency of 434 MHz. An
RF transmitter receives serial data and transmits it wirelessly through RF
through its antenna connected at pin4. The transmission occurs at the
rate of 1Kbps ‐ 10Kbps.The transmitted data is received by an RF receiver
operating at the same frequency as that of the transmitter.
The RF module is often used along with a pair of encoder/decoder. The
encoder is used for encoding parallel data for transmission feed while
reception is decoded by a decoder. HT12E‐HT12D, HT640‐HT648, etc. are
some commonly used encoder/decoder pair ICs.

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RELAY
A relay is an electrically operated switch. Many relays use
an electromagnet to mechanically operate a switch, but other operating
principles are also used, such as solid‐state relays. Relays are used where
it is necessary to control a circuit by a low‐power signal (with complete
electrical isolation between control and controlled circuits), or where
several circuits must be controlled by one signal. A relay switches one or
more poles, each of whose contacts can be thrown by energizing the coil.
Normally‐open (NO) contacts connect the circuit when the relay is
activated; the circuit is disconnected when the relay is inactive. It is also
called a "Form A" contact or "make" contact. NO contacts may also be
distinguished as "early‐make" or "NOEM", which means that the contacts
close before the button or switch is fully engaged. Normally‐closed (NC)
contacts disconnect the circuit when the relay is activated; the circuit is
connected when the relay is inactive. It is also called a "Form B" contact
or "break" contact. NC contacts may also be distinguished as "late‐break"
or "NCLB", which means that the contacts stay closed until the button or
switch is fully disengaged. SPDT ‐ Single Pole Double Throw, a common
terminal connects to either of two others. Including two for the coil, such
a relay has five terminals in total.
RELAY DRIVER ULN2003A
The ULN2003A is a high‐voltage, high‐current Darlington transistor array. It
consists of seven NPN Darlington pairs that feature high‐voltage outputs with
common‐cathode fly back diodes for switching inductive loads. The drivers can
be paralleled for higher current capability, even stacking one chip on top of
another, both electrically and physically has been done. Generally it can also be
used for interfacing with stepper motor, where the motor requires high ratings
which cannot be provided by other interfacing devices.
Features
 500 mA rated collector current (single output)
 50 V output
 Includes output fly back diodes
 Inputs compatible with various types of logic
Typical usage of the ULN2003A is to drive relays, lamp and LED
displays or stepper motors Logic buffers, Line drivers, Hammer driver.

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CIRCUIT DIAGRAM
TRANSMITTER RECEIVER

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WORKING
This circuit utilizes the RF module (Tx/Rx) for making a wireless remote, which could be used
to drive an output from a distant place. RF module, as the name suggests, uses radio frequency
to send signals. These signals are transmitted at a particular frequency and a baud rate. A
receiver can receive these signals only if it is configured for that frequency. A four channel
encoder/decoder pair has also been used in this system. The input signals, at the transmitter
side, are taken through four switches while the outputs are monitored on a set of four LEDs
corresponding to each input switch. The circuit can be used for designing Remote Appliance
Control system. The outputs from the receiver can drive corresponding relays connected to
any household appliance.
This radio frequency (RF) transmission system employs Amplitude Shift Keying (ASK) with
transmitter/receiver (Tx/Rx) pair operating at 434 MHz. The transmitter module takes serial
input and transmits these signals through RF. The transmitted signals are received by the
receiver module placed away from the source of transmission. The system allows one way
communication between two nodes, namely, transmission and reception. The RF module has
been used in conjunction with a set of four channel encoder/decoder ICs. Here HT12E &
HT12D have been used as encoder and decoder respectively. The encoder converts the
parallel inputs (from the remote switches) into serial set of signals. These signals are serially
transferred through RF to the reception point. The decoder is used after the RF receiver to
decode the serial format and retrieve the original signals as outputs. These outputs can be
observed on corresponding LEDs.
Encoder IC (HT12E) receives parallel data in the form of address bits and control bits. The
control signals from remote switches along with 8 address bits constitute a set of 12 parallel
signals. The encoder HT12E encodes these parallel signals into serial bits. Transmission is
enabled by providing ground to pin14 which is active low. The control signals are given at pins
10‐13 of HT12E. The serial data is fed to the RF transmitter through pin17 of HT12E.
Transmitter, upon receiving serial data from encoder IC (HT12E), transmits it wirelessly to the
RF receiver. The receiver, upon receiving these signals, sends them to the decoder IC (HT12D)
through pin2. The serial data is received at the data pin (DIN, pin14) of HT12D. The decoder
then retrieves the original parallel format from the received serial data.
When no signal is received at data pin of HT12D, it remains in standby mode and consumes
very less current (less than 1μA) for a voltage of 5V. When signal is received by receiver, it is
given to DIN pin (pin14) of HT12D. On reception of signal, oscillator of HT12D gets activated.
IC HT12D then decodes the serial data and checks the address bits three times. If these bits
match with the local address pins (pins 1‐8) of HT12D, then it puts the data bits on its data
pins (pins 10‐13) and makes the VT pin high. An LED is connected to VT pin (pin17) of the
decoder. This LED works as an indicator to indicate a valid transmission. The corresponding
output is thus generated at the data pins of decoder IC. A signal is sent by lowering any or all

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the pins 10‐13 of HT12E and corresponding signal is received at receiver’s end (at HT12D).
Address bits are configured by using the by using the first 8 pins of both encoder and decoder
ICs. To send a particular signal, address bits must be same at encoder and decoder ICs. By
configuring the address bits properly, a single RF transmitter can also be used to control
different RF receivers of same frequency.
To summarize, on each transmission, 12 bits of data is transmitted consisting of 8 address bits
and 4 data bits. The signal is received at receiver’s end which is then fed into decoder IC. If
address bits get matched, decoder converts it into parallel data and the corresponding data
bits get lowered which could be then used to drive the LEDs.
Amplitude Shift Keying (ASK)
It is a form of amplitude modulation that represents digital data as variations in
the amplitude of a carrier wave. In an ASK system, the binary symbol 1 is represented by
transmitting a fixed‐amplitude carrier wave and fixed frequency for a bit duration of T seconds.
If the signal value is 1 then the carrier signal will be transmitted; otherwise, a signal value of 0
will be transmitted.
Antenna Specification
‐ The recommended length of the antenna is 17cm.
‐ Coiling the antenna up will shorten the range.
‐ For best reception mount it vertical and on a suitable ground plane, (a conducting surface)
as high as one can manage.
IMPLEMENTATION AND TESTING
The circuit is simulated using NI Multisim and the transmitter and receiver circuits were
tested on breadboard. The final circuit was implemented on Vero‐board by manual
Soldering. After soldering the components on to the PCB, the boards were thoroughly cleaned
for removing any residual flux and wire leads. All the components are checked for their values
and proper orientation if applicable. Before ICs were inserted into the sockets, power was
applied to the board and voltages were measured at the IC power points. Other DC voltages
were also checked if possible. Then power was removed from the board, and ICs were inserted
into the sockets, checking the proper orientation. Power was again applied to the board
expected voltages and signals were monitored. The supply voltages were monitored and
verified. Working was tested and the product was completed.

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APPLICATIONS
 Radio remote control is used to control distance objects using a variety of radio signals
transmitted by the remote control device. As a complementary method to infrared remote
controls, the radio remote control is used with electric garage door or gate openers,
automatic barrier systems, burglar alarms and industrial automation systems.
 Home appliances control and industrial applications
 RF is used in jamming circuit for military purposes.
 A remote controlled device primarily saves a lot of time and energy. Its significance in
today’s world is immense when people don’t have to unnecessarily waste their time in
operating the appliances by being near to the appliance. They can operate it while they’re
engrossed in whatever task they’re doing and don’t have to bother leaving it in between.
 The remote control can extend up to a long distance depending on the frequency used
and the efficiency of the circuit. It is an advantage that it can be operated from distances.
 Tediousness of operating the appliance in its close proximity is done away with. The circuit
has the advantages that it can be easily implemented using easily available and low cost
components. The maintenance is also easy.
Advantages
‐ Highly Sensitive
‐ Very low noise
‐ Low cost and reliable circuit
‐ The appliances can be controlled from 100 meters range. Further range can be extended
to a larger distance by increasing the height of antenna.
‐ Can handle heavy loads up to 7 Amperes.
CONCLUSION
The product to demonstrate the remote controlled operation of multiple home appliances is
designed.

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REFERENCES
1. http://arif‐ece.blogspot.com/2010/05/tv‐remote‐controlled‐home‐appliance.html
2. http://arif‐ece.blogspot.com/2010_05_01_archive.html
3. http://www.circuitstoday.com/category/remote‐circuits
4. http://www.satsleuth.com/schematics.htm
5. http://www.printsasia.com/book/Electronic‐Projects‐for‐Beginners‐Using‐Easily‐
AvailableElectronic‐Components‐with‐A‐Primer‐on‐Basic‐8122301525‐9788122301526
6. http://www.dapj.net/hobby/?paged=2
7. http://extremeelectronics.co.in/