Wireless Communication. Setting up simple wireless communication.

Note: The tutorial over wireless communication is the upgrade over my last post which was on Encoding-Decoding signals. The circuit here shows how to send the same encoded signals of that circuit without wires.Please go through my last post to learn how to make encoding decoding circuit.Click here, and if you already finished that, go on reading. Rest, alright!

What we will do:

Hey awesome guys...how are you. I am Vkas and after a small break I am ready for the next tutorial. Today I will go through the basics of wireless communication and show how to make circuit that can communicate wirelessly.

But before going ahead, I want to share a little update that took place in my life. I have joined masters program at Manipal University with Embedded systems as my specialization. I am really excited to study at one of the premier university of India...

Switching back to tutorials, wireless is the age we are living. I don’t think there is any need to describe what wireless is and what wireless devices we are using, what we are keen to know is how we ourselves can make a device that can send signals over wireless medium i.e. air.

The device we are going to make today can communicate in the range of 30 meters and the circuit is the upgrade over encoding-decoding circuit from my last post.

What it is...and How it is...:

There are two sides of communication, a Transmitter side which transmits the signal and the receiver side which receives the transmitted signal. For an instance, right now you are reading my blog. Here, I am transmitting the posts through internet on your computer screen and you are receiving these posts through your eyes and brain.

From our today’s small range circuit to NASA’s mars robots all have a transmitter (Tx) and a receiver unit (Rx).

The communication that takes place between Tx and Rx can be one way or two ways. One way communication is like your television remote. You can operate television through it but cannot do the same through the television. So, in the sense, communication is taking place in one way i.e. from remote to television.

On the other hand, two way communications can be understood by an example of mobile phone, were you can send the signal (your voice) and receive the signal (voice from another end).

In today’s post, we will learn how to do One Way communication.

The Modules:

The job of transmitting and receiving the desired signal is done through modules. In market they are available with the name – ‘RF modules 434Mhz’. The module comes in a pair and looks like the one shown below:

The word RF stands for “Radio Frequency”. The radio frequency has ability to cross obstacles plus it provides good coverage, 30 meters is actually good range when working at ground-zero level.

The RF Tx-Rx is used to transmit serial data. In simple language, you can send one signal at a time. Now let’s understand what technique it uses to make signals wireless:

Technique involved behind the scene of wireless transmission:

Before spitting the words like modulation, carrier frequency and message signals, I want to talk about Tortoise and the Crocodiles. Yes, you read it correct and I am damn serious and sure that you will understand the concept behind wireless transmission after reading this small “FACT”.

In forests of Amazon, crocodiles used to lay their eggs at the bank of river. Now, tortoises also live in same river but the fact is that tortoises are not so concern about their babies I mean they don’t take care of them after laying eggs. So, to give a small assurance to themselves that at least their babies can reach to the river and not get eaten up by birds and other animals, mamma tortoise lay her eggs in the nest of crocodiles. Now, what happens is when babies come out of the egg shells, the mamma crocodile takes babies of tortoise with her own babies to the river. Now, don’t think that why she is not eating them because according to science, mamma crocodile thinks that tortoises are also their babies. (Yup! they can eat them afterwards when she realize how stupid she was!)

Returning back to our topic, digital signals or message signals are not capable of traveling long distances in wireless medium. To take these signals to receiver a carrier is required which can deliver them to the receiver end. This carrier is called as carrier frequency which is in sinusoidal form. Now comparing this with our crocy-torty story, the baby tortoise is our message signal. Since it is not capable to reach the river of its own, mamma crocodile acts as a carrier frequency that carries the baby tortoise to the river (that is our receiver).

So, this is how transmission of digital signals takes place. Now comes another part which is different techniques of sending this modulated signal. Hey, I am not going over every technique but just for you knowledge, the digital modulation techniques are:

Amplitude Shift Keying (ASK)

Frequency Shift Keying (FSK), and

Phase Shift Keying (PSK)

The transmitter-receiver module that we are using today works on “Amplitude Shift Keying (ASK)” technique to establish wireless communication. Actually ASK is the most basic and simplest technology used to transmit signals over wireless or wired medium. Amplitude is the property of any waveform that represents the magnitude of waveform. I know this is going pretty nerd, so have a look at the animation below:

In ASK technique, a message signal and the carrier signal are blended together (modulated) and then sent through an on-off switch. As the switch is pushed that is turned ON, the modulated signal gets transmitted which is received at the receiver side as binary 1 and when the switch is released that is turned OFF, it represents a binary zero at the receiver end. Due to this On-Off technique, the ASK technique is also called as On-Off keying.

Now, as we know the technology working behind the wireless RF transmission. Let’s have a look at the modules we are going to use in our tutorial.

When observing the receiver-transmitter pair, you will notice a metal component on its surface; this part is called the oscillator. Remember, in our last tutorial I gave a brief explanation about it. This oscillator part is responsible for generating sinusoidal waves. Now, observe the receiver part, it is little bigger than the transmitter, it also have an oscillator and the IC present on its chip removes the message signal from the carrier frequency and gives out the data at Data out (D-out) pin.

The last the most important thing left is the Antenna part, i will explain it during practical implementation of circuit.

The components you will require:

1. Encoder-Decodercircuit from the previous tutorial.

2. Breadboard (one extra, for receiver circuit)

3. RF module 434MHz. (Transmitter-Receiver pair)

4. Battery 9volts.

5. Enthusiasm (important one by the way!)

If you have the circuit from previous tutorial than before making connections on breadboard, remove the wire that connects encoder-decoder data pins, Take off your entire decoder circuit (HT12D, resistors, etc.) and place it on another breadboard which will act as receiver. Now what you will have is two separate breadboards. One act as transmitter and other one as receiver.

Making Transmitter part:

Step 1.

Take the Encoder part, insert the transmitter module nearIC HT12E and connect the data out pin of the IC to the Data in pin of the transmitter. Leave the antenna pin as it is we will get back to it at last. Also provide it with proper biasing as shown in image below:

Step 2.

Completing the transmitter part, now take the decoder part that is our data decoding IC HT12D. Insert the receiver module near to it and provide it with proper biasing by connecting vcc and ground. Connect theHT12D decoder’s Data-in pin with the receiver’s Data-out pin and that’s it, our receiver part is also ready.

Leave the antenna pin for the moment. Keep all other components from the previous tutorial as it is. Do not take them out from the breadboard and we are done!

Step 3.

Now connect the circuit with the power supply. If you followed all the steps with due respect, you will see that VT pin of the decoder pin starts glowing. This pin is showing that the encoder and decoderare in coverage area and is ready to receive the data from the transmitter side. After this happens, push the reset buttons you connected at the encoder part and you will see that LED corresponding to the switch turns ON.

Step 4.

Now, while testing the circuit, take the transmitter to some distance or bring any obstacle between transmitter receiver, you will see that the LED connected at VT pin starts blinking or sometimes turns OFF. This is happening because we have not yet connected Antenna to the modules. So, let’s see how we calculate the size of antenna and connect it to the module:

Calculating length of RF Antenna:

Whether it is big antennas at radio or TV station or a small one like our circuit, the value of antenna is calculated using same method.

Wavelength of antenna is equal to the ratio of frequency on which our device is working and the speed of light. Therefore:

λ = f/c

λ = 434000000/300000000

So, λ = 1.44 meters

To have best range, the antenna should be one-fourth of the antenna size. Such that:

Size of antenna = λ/4

Hence, 1.44/4=0.36 meters or 36 cm.

Therefore size of antenna should be 36 cm.

So, now we know the length of antenna, we will now make one, well it is very simple. Take a 36 cm long single core wire (same wire you are using in breadboard connection) and insert it in the antenna pin of transmitter. Do the same with another antenna of 36 cm at the receiver end.

Test the circuit by taking transmitter at some distance. You will notice enhanced connectivity and your circuit will become capable of crossing any obstacle in between.

So, from today’s post, we saw a very basic wireless circuit. We will go advance in coming up tutorials when I will show you how to make a wireless robot.

Yep, circuit diagram, the moral of the story is shown below:

Transmitter Circuit: