Electromagnetic Waves also called Electromagnetic Radiations are basically defined as
superimposed oscillations of an Electric and a Magnetic Field in space with their direction of
propagation perpendicular to both of them. In simple words, electromagnetic waves are
oscillations produced due to crossing over of an electric and a magnetic field.
The direction of the propagation of such waves is perpendicular to the direction of the force of
either of these fields as seen in the above figure. Like all waveforms, these have some
properties as well. Let us have a look at the properties of electromagnetic wave propagation.
Properties of Electromagnetic Wave Propagation
These waves travel at the speed of light.
These waves do not require any medium for propagation.
Electromagnetic waves travel in a transverse form.
Electromagnetic waves are not deflected by electric or magnetic field.
These waves can be polarized.
Electromagnetic Waves undergo interference and diffraction.
The wavelength(λ) and frequency (v) of the EM waves can be related as:
c= v.λ
where c = velocity of the wave.
Antenna is a metal rod or dish that catches radio waves and turns them into electrical signals
feeding into something like a radio or television or a telephone system. Antennas like this are
sometimes called receivers. A transmitter is a different kind of antenna that does the opposite job
to a receiver: it turns electrical signals into radio waves so they can travel sometimes thousands
of kilometers around the Earth or even into space and back. Antennas and transmitters are the
key to virtually all forms of modern telecommunication.
Transmitter and receiver antennas are often very similar in design.
Working of the circuit
Transmitter section - This section comprises of a HT12E encoder chip, RF transmitter and
Antenna are shown below
a) HT12E Encoder - The HT12E IC converts the parallel data into serial data for passing it to
the RF transmitter. HT12E encoder IC belongs to the 212 series of encoders. It is paired with 212
series of decoders having the same number of addresses and data format. These ICs are mainly
used for interfacing RF and infrared circuits. HT12E is capable of encoding 12 bits, out of them
8 are address bits and 4 are data bits. Thus the encoded signal is a serialized 12-bit parallel data
comprising of 4-bit data to be transferred appended with the address byte. The pin diagram and
configuration of HT12E are shown below
Figure 1 Pin diagram and pin configuration
b) RF Transmitter - The RF transmitter consists of an electrical oscillating circuit which
generates the radio wave, a modulator which perform hybrid ASK modulation of the wave
according to the digital data received from the encoder, and an amplifier which increases the
strength of modulated signal for transmission.
The RF transmitter module is a small PCB sub assembly. The pin configuration of transmitter
module is as follow - :
PIN NO. FUNCTION NAME
1 Ground(0V) Ground
2 Serial data input pin Data
3 Supply Voltage ; 5V VCC
4 Antenna output pin ANT
The serialized data from encoder is received at pin 2 of the module and passed on to the antenna
from pin 4 of the module.
Transmitter design
Receiver
This section comprises of Antenna, RF receiver and HT12D decoder chip. The modulated RF
signal is received by the antenna and passed to the RF receiver.
a) RF Receiver - The RF receiver consists of an amplifier that amplifies the received signal, a
demodulator or detector which extracts the modulated signal from the carrier wave, a modulated
signal amplifier and an output transducer.
There are two types of RF receivers - Super heterodyne receiver and super regenerative receiver.
The receiver module has 8 pins and has following pin configuration.
PIN NO. FUNCTION NAME
1 Ground(0V) Ground
2 Serial Data output pin Data
3 Linear output pin ; not connected NC
4 Supply voltage ; 5V VCC
5 Supply Voltage ; 5V VCC
6 Ground(0V) Ground
7 Ground(0V) Ground
8 Antenna input pin ANT
The carrier wave from the antenna is received at the pin 8 of the module. The extracted data in
serial form is output at pin 2 of the module.
b) HT12D Decoder - The signal extracted from the RF receiver is passed to the HT12D decoder.
It converts the serial data back to the parallel data after separating data and addresses. HT12D
belongs to the 212 series of decoders and can be paired with 212 series of encoders having the
same number of addresses and data format. HT12D is capable of decoding 12 bits, out of them 8
are address bits and 4 are data bits. The 4-bit data is of latch type and when passed to the output
data pins it remains unchanged until the new data is received.
The pin diagram and configuration of HT12D is as follows - :
There are two types of RF receivers - Super heterodyne receiver and super regenerative receiver.
The receiver module has 8 pins and has following pin configuration.
PIN NO. FUNCTION NAME
1 Ground(0V) Ground
2 Serial Data output pin Data
3 Linear output pin ; not connected NC
4 Supply voltage ; 5V VCC
5 Supply Voltage ; 5V VCC
6 Ground(0V) Ground
7 Ground(0V) Ground
8 Antenna input pin ANT
The carrier wave from the antenna is received at the pin 8 of the module. The extracted data in
serial form is output at pin 2 of the module.
b) HT12D Decoder - The signal extracted from the RF receiver is passed to the HT12D decoder.
It converts the serial data back to the parallel data after separating data and addresses. HT12D
belongs to the 212 series of decoders and can be paired with 212 series of encoders having the
same number of addresses and data format. HT12D is capable of decoding 12 bits, out of them 8
are address bits and 4 are data bits. The 4-bit data is of latch type and when passed to the output
data pins it remains unchanged until the new data is received.
The pin diagram and configuration of HT12D is as follows - :
The data in this RF module is transmitted as 4-bit data. The data to be transferred is hard-wired
with the help of switches at pins 10 to 13 of the HT12E IC designated as D0 to D3 respectively
according to the pin configuration of the IC. Here 10K ohm resistors are used at data pins as
pull-up resistors. The address of the transmitter is also hard-wired. Here all address pins are
grounded to allot transmitter an address of 0x00. The pin 14 of the IC is grounded to enable
transmission as it is active LOW. A switch can also be connected to pin 14 of the IC to reset
transmission. To set the oscillator, a resistor from 750MΩ to 1MΩ can be connected between pin
15 and 16 of the encoder IC. Here a 1MΩ resistor is used in the circuit. The serialized data is
passed on from pin 17 of the encoder IC to the pin 2 of the RF transmitter. A modulated carrier
wave is output from pin 4 of the RF transmitter and transmitted through the antenna.
At the receiver end, the modulated carrier wave is detected by the receiver antenna and passed on
to pin 8 of the RF receiver. The demodulated signal is output from pin 2 of the RF receiver
which is sent to pin 14 of HT12D decoder IC for converting to parallel data from the serial form.
A resistor between 30KΩ to 50KΩ can be connected between pins 15 and 16 of the decoder IC
to match the oscillator settings. Here, a 50KΩ resistor is used in the circuit. These values of the
resistances are dictated as according to the datasheets of HT12E and HT12D ICs. The address at
the decoder IC is again hard wired and should match with the address at encoder IC to enable the
pairing of transmitter and receiver.
Here all address pins are grounded to match the 0x00 address at the transmitter end. The received
data is fetched at pins 10 to 13 of HT12D which are designated as D0 to D3 respectively
according to the pin configuration of the decoder IC. In the experiment, received data is detected
with the help of LEDs. An LED serially connected to a 1KΩ pull-up resistor is interfaced to each
data pin to detect the digital signal at the respective pin. If the LED glows that means a HIGH
signal is receiving at that pin else a LOW signal is receiving at that pin. As the data is changed at
the encoder IC on altering the on/off status of the switches at data pins of the encoder IC, a
similar change in the on/off status of the LEDs connected to data pins of the decoder IC is
reflected.
