In this essay we will talk
about some general aspects when making cheap wireless communications systems
between low-cost embedded microprocessors, using in the code, the new library “RadioHead”.
We will focus in a famous platform based on Atmel embedded microprocessors
called Arduino working with the cheapest RF transmitters that use ASK
Modulation for setting up the essentials components of a functional low-cost
communication system. Firstly we have to tell some general aspects about the
platform we are going to use.
Arduino is a free embedded
microprocessors hardware platform that allows making easily, projects that need
the interaction of software and hardware. This platform has a big community of
users and also a lot of documentation, libraries, tutorial and examples, that
can be found in their web page. Furthermore, that platform is very cheap so is
suitable for any type of D.I.Y projects.
For wire communication systems,
Arduino Boards have an UART port for serial communication. In addition, some
Arduinos Boards as Arduino Mega or Arduino Due, have more than one UART port
and you can also make Virtual Ports with “SoftwareSerial.h” library in any
Arduino Board.
The problem with these
communication ports are that they cannot be use when we want to make wireless
communications. These types of communications need some codification in order
to detect corrupt messages and remove interference noise. These problems are
not frequent in wire communications but are very common in wireless
communications. So for wireless communication systems we need extra hardware
and also extra software to manage this hardware.
Around April 2014, Mike
McCauley published the first release of “RadioHead.h”, a new library that
allows making easily wireless communications between embedded microprocessors
as Arduino. The library can be used with a lot of transmitters and receivers of
data. That library will help solve the problems that appear when we star using
wireless communication systems.
In this essay we will implement
a system based in ASK modulation hardware but others are supported as well. We
select ASK because they are the cheapest ones, about 2$ each pair of Transmitter
(TX) and Receiver (RX) with a real range about 50 meters. With two Arduinos
micro of 3$ each and some batteries, we will have a complete wireless
communication system. This is the best hardware for making our first functional
wireless communication system. For this system any Arduino board is suitable,
if you are prototyping probably an Arduino Uno will be the best choice instead
of choosing an Arduino Micro which is normally used for finished projects. In
this part of the essay we are going set up the simplest wireless communication
system using the knowledge and the hardware presented above.
Firstly, after having selected
the hardware, we are going to set up all the connections that are needed in
order to start working with the hardware.
We just need 3 wires for each module. Two of them for
powering the TX/RX connected to the pins of the Arduino 5+ and Gnd, and the
other for passing the data. In our system we will use default pins, D12 in TX
and D11 in RX for transmitting the data.
Secondly, we have to start
working on the software but first we need some general knowledge about
Radiohead library. The library has two parts. The first one is “Drivers” and
the other is “Managers”. For working with this library you have to choose one
driver and one manager. This design of the library is very useful because if
you improve your hardware you will just need to change the driver and not to
change all the code, which in most cases is very complex.
In our case we selected the
“RH_ASK.h “driver, if we want to use other hardware we just change the driver
that the hardware we selected needs. We also need a manager, as you have read
above. In our case we will use the simplest one “RHDatagram”.
Without entering in complex
details about the code, we are going to update the example to test that the
hardware is wire correctly and prove if or system is functional or not. So,
we plug both Arduinos to the computer and using Arduino IDE (for more
information about basic use of Arduino check Arduino.cc) upload the example
codes that you will find in the Radiohead library (the links are below).
If everything is okay you will
receive in your RX module the string “Hello World”. In this case you have
successfully implemented your low cost communication system using the new
library Radiohead. Now you can improve it by changing the managers and making
strongest communications.
For concluding, we have seen
that wireless communication systems between low-cost embedded microprocessors are
complex than wire communication systems, because they need extra hardware and
software in order to work. Using the previous concepts we have made our
low-cost platform using Arduino with a pair of ASK Modules and the RadioHead library
that helps to deal with all the typical problems in our wireless communication system.
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