During 2018, mi remote instructor Luis Carvao suggested to me the idea to complete the assignment with something usefull for my final project so he proposed to me a challenge that of course i can´t to decline so i bought a pair of trasnmitter and receivers with the idea to make a Wireles Communication with this popular modules :

The first reference i followed was trought "Seed Studio Oficial Wiki website" where they described their products :

For learn about them i was reading the things founded there but it not was much information:

SPECIFICATION

Frequency: 433Mhz.

Modulation: ASK

Receiver Data Output: High - ½ Vcc, Low - 0.7v

Transmitter Input Voltage: 3-12V (high voltage = more transmitting power)

Receiver Input Voltage : 3.3-6V (high voltage = more receiving power)

DEMOSTRATION SCHEME

So i founded another information more helpfull for learn things such as radio communications between two AVR microcontrollers can be easy when specialized modules are used.

Transmitter and receiver modules are tuned to work correctly at 433.92MHz. Transmitter can be powered from 3 to 12V power supply while receiver accepts 5V. 5V is common for AVR microcontrollers so no problems with interfacing.

Modules don't require addition components, just apply power and connect single data line to send information to/from and that's it. For better distances apply 30 – 35cm antennas. Modules use Amplitude-Shift Keying(ASK) modulation method and uses 1MHz bandwidth.

Radio transmission is a bit more complicated than wired communications because you never know what radio signals are present on air. So all matters how transmitted signal is encoded.

Two considerations which will expand the range and efficiency of these two devices. First of all, each transmitter device has ansupply voltage range of 2 – 12 volts. The higher the voltage, the stronger the signal strength. Commonly, the microcontrollers run at 5 volts, so must to do separate power, either from a non-voltage resisted incoming voltage, or a separate power supply sharing a common ground.

These devices take very little amperage, consider using a 12 volt power supply, and running voltage directly from it to the transmitter, while isolating the other circuitry's voltage through a voltage regulator.

I learned that this devices can to work very reliably when are close to each other on a table but when they are separated they were able to communicate, but approximately 20% of messages were corrupted.

These modules can work well for low performance, non-critical applications. For more demanding applications, more sophisticated (and more expensive) RF modules should be considered.

TRANSMITTER FEATURES

RECEIVER FEATURES

WIRING

So first i made was conected both to 2 microcontrollers as arduino with the idea to implemented them later on my final project boards powering them with to 9V supply batteries :

For programm the modules with arduino, i must to install some libraries first :

VIRTUAL WIRE LIBRARY

VirtualWire is an Arduino library created by Mike McCauleythat provides features to send short messages, without addressing, retransmit or acknowledgment, a bit like UDP over wireless, using ASK (amplitude shift keying).

Does not use the Arduino UART. Messages are sent with a training preamble, message length and checksum. Messages are sent with 4-to-6 bit encoding for good DC balance, and a CRC checksum for message integrity.

Why not just use the Arduino UART connected directly to the transmitter/receiver? :

" ASK receivers require a burst of training pulses to synchronize the transmitter and receiver, and also requires good balance between 0s and 1s in the message stream in order to maintain the DC balance of the message."

I downloaded it from here : Virtual library

LEARNING TROUGHT FUNCTIONS LIBRARY

 #include < VirtualWire.h  

To select the Transmitter Data Pin , void :

vw_set_tx_pin

To select the Receiver Data Pin , void :

vw_set_rx_pin

Setup the speed of transmission , The speed of Tx must be as same as On Rx .The speed will be a Number of Bit Per Second between 0-9600 , for short distance you can use fast speed , For long distance "Up to 90m" you must use lower transmission speed as much as possible :

vw_setup(uint16_t speed);

Start the receiver PLL running ,You must do this before you can receive any messages :

vw_rx_start();

You must do this before you can receive any messages. When a messageis available (good checksum or not), vw_have_message() will return true :

vw_rx_stop();

Block and wait until the transmitter is idle,called :

vw_wait_tx();

Block and wait until a message is available from the receiver, call :

vw_wait_rx();

Send a message with the given length, call :

vw_send(uint8_t* buf, uint8_t len);

Returns true if an unread message is available from the receiver.,call :

vw_have_message();

So i decided to use the reference programm modified by me for the transmitter with the idea to send a character as a number 1 and after 3 seconds will to send a 0 and then will to start the transmission.

//simple Tx on pin 12
//Written By : Mohannad Rawashdeh Modified by Pilar Caballero
#include < VirtualWire.h  
char *controller;

void setup() {
pinMode(13,OUTPUT);
vw_set_ptt_inverted(true); //
vw_set_tx_pin(12);
vw_setup(4000);// speed of data transfer Kbps
}

void loop(){
controller="1" ;
vw_send((uint8_t *)controller, strlen(controller));
vw_wait_tx(); // Wait until the whole message is gone
digitalWrite(13,1);
delay(3000);
controller="0" ;
vw_send((uint8_t *)controller, strlen(controller));
vw_wait_tx(); // Wait until the whole message is gone
digitalWrite(13,0);
delay(3000);

}

In this is the code for the Receiver :

//simple Tx on pin D12

//..................................
#include < VirtualWire.h 
void setup(){
vw_set_ptt_inverted(true); // Required for DR3100
vw_set_rx_pin(12);
vw_setup(4000); // Bits per sec
pinMode(13, OUTPUT);

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, &buflen)) {
if(buf[0]=='1'){
digitalWrite(13,1);
} 
if(buf[0]=='0'){
digitalWrite(13,0);
}
 }
  }

PROGRAMMING MY BOARDS

Hello World Transmitter Exercise :

Message Transmitter Program:

#include VirtualWire.h 

void setup(){
    Serial.begin(9600);	  // abre el puerto de serie
    Serial.println("Transmisor listo"); // Imprime "listo" en el monitor serial
    pinMode(13, OUTPUT); //configura el pin 13 como salida, se usara el led integrado.
   
    vw_set_tx_pin(12);          // Configura el pin 12 como TX
    vw_set_ptt_inverted(true);  // Requerido para DR3100
    vw_setup(2000);	        // Bits por segundo
}

void loop(){
    digitalWrite(13, HIGH);      // Parpadeo para mostrar actividad
    char msg[] = "Faito Kite is talking";   // Mensaje a enviar
    vw_send((uint8_t *)msg, strlen(msg)); //Enviando...
    vw_wait_tx(); // espera hasta que el mensaje se haya enviado
    Serial.println("Transmitiendo..."); // Imprime transmitiendo en el monitor serial
    delay(125);                 // Pausa antes repetir el ciclo
    digitalWrite(13, LOW);      // Parpadeo para mostrar actividad
    delay(125);                 // Pausa antes repetir el ciclo
         
} 

Receiver Program:

#include VirtualWire.h 

int count;

void setup(){
    Serial.begin(9600);	// abre el puerto de serie
    Serial.println("Receptor listo"); //Imprime "listo" en el monitor serial
    pinMode(13, OUTPUT); //configura el pin 13 como salida, se usara el led integrado.
    
    vw_set_rx_pin(12);       //Configura el pin 12 como TX
    vw_set_ptt_inverted(true); //Requerido para DR3100
    vw_setup(2000);	     //  Bits por segundo
    vw_rx_start();       // Inciar el receptor
}

void loop(){
    digitalWrite(13, HIGH);      // Parpadeo para mostrar actividad
    //uint8_t buf[VW_MAX_MESSAGE_LEN] = {};
    uint8_t buf[VW_MAX_MESSAGE_LEN]; //Almacenar en buffer los datos recibidos
    uint8_t buflen = VW_MAX_MESSAGE_LEN; //Determina el numero de caracteres recibidos
    if (vw_get_message(buf, &buflen))   {// Si hay un mensaje recibido ejecuta...
  
	int i; 
  Serial.print("Rx: "); //imprime Rx en el monitor serial
	
	for (i = 0; i < buflen; i++)  {  //rutina para impresion del mensaje recibido

  char c = (buf[i]); // guarda el caracter recibido para despues imprimirlo
  Serial.print(c); //imprime el caracter recibido en el monitor serial
	Serial.print(""); //deja un espacio en el monitor serial
	}
  count++;  //incrementa contador
  Serial.print(count);  //imprime el contador en el monitor serial
	Serial.println("");   // salto de linea monitor serial
    }
    
delay(125);                 // Pausa antes repetir el ciclo
digitalWrite(13, LOW);      // Parpadeo para mostrar actividad
delay(125);                 // Pausa antes repetir el ciclo
}

Results

After some attemps later i decided to change the speed of transmissions to 4000 bits per second but nothing happens.

MY FINAL PROJECT

Thinking in my final Project i begin with the CO2 Sensor Callibration explained in my

Final Project Process Page at Programming processes section.

MY SENSOR:

References about Gas Sensors

I found at the Arduino Offical Web page some refrences about the use of this kind of sensors, there you can find basic overwiew with data sheets about the family but i decided copied to this page for never forget the basics things :

Introduction

The MQ series of gas sensors use a small heater inside with an electro-chemical sensor. They are sensitive for a range of gasses and are used indoors at room temperature.

They can be calibrated more or less (see the section about "Load-resistor" and "Burn-in") but a know concentration of the measured gas or gasses is needed for that.

The output is an analog signal and can be read with an analog input of the board i designed.

Read the datasheet

Try to find a few datasheets for the sensor, and read them careful.

Since there are no electronic components inside, therefor most sensors can be used with AC and DC voltages.

Be careful when connecting it for the first time. If the pins are connected wrong, the sensor could get damaged, or it could be broken instantly. There are also shields available with these sensors pre-installed.

Wiring

The preferred wiring is to connect both 'A' pins together and both 'B' pins together. It is safer and it is assumed that is has more reliable output results. Although many schematics and datasheets show otherwise, you are advised to connect both 'A' pins together and connect both 'B' pins together.

In the picture, the heater is for +5V and is connected to both 'A' pins. This is only possible if the heater needs a fixed +5V voltage.

The variable resistor in the picture is the load-resistor and it can be used to determine a good value. A fixed resistor for the load-resistor is used in most cases.

The Vout is connected to an analog input of the Board designed

The heater

The voltage for the internal heater is very important.

Some sensors use 5V for the heater, others need 2V. The 2V can be created with a PWM signal, using analogWrite() and a transistor or logic-level mosfet.

The heater may not be connected directly to an output-pin of the Arduino, since it uses too much current for that.

Some sensors need a few steps for the heater. This can be programmed with an analogWrite() function and delays. A transistor or logic-level mosfet should also in this situation be used for the heater.

If it is used in a battery operated device, a transistor or logic-level mosfet could also be used to switch the heater on and off.

The sensors that use 5V or 6V for the internal heater do get warm. They can easily get 50 or 60 degrees Celcius.

After the "burn-in time", the heater needs to be on for about 3 minutes (tested with MQ-2) before the readings become stable.

Load-resistor

The sensor needs a load-resistor at the output to ground. It's value could be from 2kOhm to 47kOhm. The lower the value, the less sensitive. The higher the value, the less accurate for higher concentrations of gas.

If only one specific gas is measured, the load-resistor can be calibrated by applying a know concentration of that gas. If the sensor is used to measure any gas (like in a air quality detector) the load-resistor could be set for a value of about 1V output with clean air.

Choosing a good value for the load-resistor is only valid after the burn-in time.

Burn-in

Some datasheets use the term "preheat", but it is the time to burn-in the sensor. This is meant to make the sensor readings more consistent. A time of 12 or 24 hours is usually used for the burn-in time.

The Burn-in is achieved by applying normal power to the sensor (to the heater and with the 'A' and 'B' pins connected, and with a load-resistor). In some special cases a specific burn-in is needed. See the datasheet if the sensor needs such a specific burn-in.

Interesting links

Machine olfaction (electronic nose) using MQ-series gas sensors:Electronic Noise

This instructable uses a Figaro sensor and explains how to use them: http://www.instructables.com/id/How-To-Smell-Pollutants/

The Figaro sensors work the same as the MQ series sensors.

Wikipedia has an article about electrochemical gas sensors: http://en.wikipedia.org/wiki/Electrochemical_gas_sensor

MQ135 : A Sensor For Air Quality

- The heater uses 5V.

An example how to use it:

Learning Basics

An example with calculation of the CO2 value:

Meter Using MQ 135.

Search for datasheet:

Meter Using MQ 135.

Networking: Master Test I from Pilu Caballero on Vimeo.

Faito v. 01 : High Bright Led Board from Pilu Caballero on Vimeo.

1TESTVOLTAGE_SERIAL from Pilu Caballero on Vimeo.

PROGRAMING INPUT DEVICES : TEST MQ135 WITH LITHIUM ION POWER SUPPLY from Pilu Caballero on Vimeo.

The processes for callibrated the sensors was a fight but finally i can detect some differents atmospherics gases. You can know more about this process in my Final Project Process Page :

Process Web Page

OUTPUT DEVICES Receives information data from INPUT DEVICE blinking bright Leds described at Electronics section with mapped values from the analog sensor.

High Bright Leds from Pilu Caballero on Vimeo.

Testing Slave Board with a Bright Led from Pilu Caballero on Vimeo.

All the Files about this programs are at my :

Final Project Page at WEEK FILES SECTION.