Tutorial: Arduino + Kit rf 433Mhz(Part3: Software)

 If you are reading this post, you have a Rf link kit working with the example code of Virtualwire. If not you should read part 2  of this tutorial. Today we are going to go through Virtualwire understanding all the functions of this library.

Virtualwire Library

Virtualwire is a library made by Mike McCauley. The library is distributed under an Open Source License. You can use it even if you are making money but you have to distribute your code with Open Source License. However, it's time to view all the functions of the library.

Transmitter 

For the transmitter we have the following functions:

• vw_set_tx_pin(pin); This function just sets the transmitter pin. The default pin is 12.
• vw_setup(uint16_t speed); is used to set the speed of the communication.
• vw_wait_tx(); is very usefull, you call it after sending the message and the arduino will wait until all the message has gone. Then the program would continue.
• vw_send((uint8_t*) message, message len);  This function is used to send the message. To understand how it works we will decompose it. The function is vw_send(); inside it you have to put the message.So, you have to put (message, message len). It's very simple. Also, you have this part  (uint8_t*), you have to write it before the message, it's like the function (byte*). 

Note: The function strlen(), is used to obtain the size of the string, the easiest way of doing that.

// transmitter.pde
//
// Simple example of how to use VirtualWire to transmit messages
// Implements a simplex (one-way) transmitter with an TX-C1 module
//
// See VirtualWire.h for detailed API docs
// Author: Mike McCauley (mikem@open.com.au)
// Copyright (C) 2008 Mike McCauley
// $Id: transmitter.pde,v 1.3 2009/03/30 00:07:24 mikem Exp $

#include <VirtualWire.h>

void setup()
{
    Serial.begin(9600);   // Debugging only
    Serial.println("setup");

    // Initialise the IO and ISR
    vw_set_ptt_inverted(true); // Required for DR3100
    vw_setup(2000);  // Bits per sec
}

void loop()
{
    const char *msg = "hello";

    digitalWrite(13, true); // Flash a light to show transmitting
    vw_send((uint8_t *)msg, strlen(msg));
    vw_wait_tx(); // Wait until the whole message is gone
    digitalWrite(13, false);
    delay(200);
}

Receiver 

The receiver have the following functions:

• vw_set_tx_pin(pin); This function just set the receiver pin. The default pin it's 11.
• vw_setup(uint16_t speed); is used to set the speed of the communication. It must be the transmitter speed.
• vw_rx_start(); You must call it before receive any data.

• vw_have_message(); Returns true if message has been received. This is similar to the "available" function of most other libraries.
• vw_wait_rx();Wait for a message to be received. This will only return when a message has been received, otherwise it will wait forever, and the  program won`t continue. 
• vw_wait_rx(timeout_ms); In this case the arduino will wait until the time waiting is more than the max time that you set.
• vw_get_message(buf, &buflen) This function is used to store the message in a string. Buf is the name of the string and buflen is name of the variable that store the maximum size of the string.Then when you need data you take from buf.
• vw_rx_stop() Disable the receiver process. 

// receiver.pde
//
// Simple example of how to use VirtualWire to receive messages
// Implements a simplex (one-way) receiver with an Rx-B1 module
//
// See VirtualWire.h for detailed API docs
// Author: Mike McCauley (mikem@open.com.au)
// Copyright (C) 2008 Mike McCauley
// $Id: receiver.pde,v 1.3 2009/03/30 00:07:24 mikem Exp $

#include <virtualwire.h>


void setup()
{
    Serial.begin(9600); // Debugging only
    Serial.println("setup");

    // Initialise the IO and ISR
    vw_set_ptt_inverted(true); // Required for DR3100
    vw_setup(2000);  // Bits per sec

    vw_rx_start();       // Start the receiver PLL running
}

void loop()
{
    uint8_t buf[VW_MAX_MESSAGE_LEN];
    uint8_t buflen = VW_MAX_MESSAGE_LEN;

    if (vw_get_message(buf, &amp;buflen)) // Non-blocking
    {
 int i;

        digitalWrite(13, true); // Flash a light to show received good message
 // Message with a good checksum received, dump it.
 Serial.print("Got: ");
 
 for (i = 0; i &lt; buflen; i++)
 {
     Serial.print(buf[i], HEX);
     Serial.print(" ");
 }
 Serial.println("");
        digitalWrite(13, false);
    }
}

Now what?

With this code you will be able to send string of data, but if you try to send a variable you will see that the Arduino IDE print some errors. In the next tutorial we will learn how to send multiple variables using Virtualwire.

Tutorial: Arduino + Kit rf 433Mhz(Part 2: Set up)

Today we are making the setting up for our RF link kit. If you don't now what's it an RF link kit please read the part 1 of this tutorial. So let's start then:

Software Set Up

Arduino Folder

First of all we have to install the library Virtualwire on the arduino IDE. We have to open a folder named "libraries" and copy the folder VirtualWire, that you download before, inside. This folder is in the arduino folder where the program files are kept. Then we have to restart the arduino IDE. Let's prepare the hardware.

Transmitter Set Up

Transmitter

First we going to set up our transmitter. In my case I will use an arduino Uno. We only need to connect the pin 12 from your arduino to the transmitter data pin. You have to look the data sheet because in function of the manufacturer the collocation of the pins could change.

If you want to have good range you should connect the transmitter to a 9v battery. This modules can be powered between 3 to 12 V. More volts means more range.If you use more than one battery you must connect the grounds, if not it won't work.

Antenna

Also, you have to put an antenna. For this modules a simple piece of wire with 15 cm long will be enough. I found some antennas for this modules, so another option it's to buy the antenna.I couldn't try them yet.

Receiver Set Up

Receiver

However, we have to connect the receiver. The connection it's similar. You have to attach the date pin to the pin 11 on your arduino board  and power the receiver. In this case you can power directly from your arduino because the receiver works with 5v. Also, you should put an antenna, the same as the transmitter will be enough.

Equal to the transmitter, the receivers from different manufactures could have different pins distributions.

Test

 Now it's time to charge the code. To be sure that all works fine, we will charge the example code. They two code examples are   File =>Examples=> VirtualWire=> transmitter   and    File => Examples=> VirtualWire=> receiver.

Then open the serial monitor and if you receive the data your set up it's correct.If not read "A tip for solve possible problems"

This all for this part of the tutorial, on the next part we will read the code and understand all the functions on the VirtualWire library. Leave some comments and propose ideas writing to controlrobotics@rodrigomompo.com

A tip for solving possible problems

A good form to test if the problem is form your code or from your hardware, its making the connection trough a wire. Again you need to make sure that all the grounds are connected if you want a positive result.

Tutorial: Arduino + Kit rf 433Mhz (Part 1: Introdución)

When you start making  more complex projects, you will probably need to read a sensor far away from your arduino or read/send information between two arduinos. Sometimes you can use a piece of wire but when you can´t use it, you will need some wireless solutions.

Kit Link Rf 433 Mhz

There are a lot of options but many of theme could be a bit expensive for some projects. Instead, you can use an  RF link kit that cost about 3$  each!!. The most common frequency is 433 Mhz but you can find 315  Mhz kits as well. Whit this kits you can send data from one arduino to  another.

How a RF link kit works  ?

This kits use only one digital pin for transmitting (TX) and one pin for receiving  (RX) the data. So, you have to take the data from one arduino, convert it in a binary sequence of 0 and 1, send it and then  when you receive the binary sequence, transform it  in data.

In the next part of this tutorial,we will start setting up the hardware and programing the software. For the next part of the tutorial you will need:

Prototyping wire Male/Female

Hardware

• Two arduinos 
• Kit Rf 433 MHz 
• Some wire 
• Two breadboards or prototyping  wire to connect the TX and RX module to the arduino

Software

• Arduino IDE
• Library VirtualWire

Welcome to ControlRobotics

Today, I'm starting a new project. In this blog I will try to resolve common problems that arise while you are  developing your home projects. Furthermore, I will post some interesting projects to do in your free time and other interesting information about  DIY electronics. However, I would like to post finished DIY projects from the followers and other interesting stuff. So you can propose your ideas and projects on google+ or send it to  controlrobotics@rodrigomompo.com.