2021-2022-BOUKEZZATA-BERTON-MESLOUH

Smart Device

Table of Contents

1. About The Project
2. Lora
3. LoRAWAN
4. KiCAD
5. Node-Red
6. DATASHEET

About The Project

After manufacturing the gas sensor, we would like to design a system from an ESP32 microcontroller to retrieve the data collected from the sensor and communicate the detection of a specefic gas towards a server with a LoRA module

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LoRA

We used the RN2483@jpmeijers library to connect the Lora module to the TTN server "The Things Network".

We've connected the 3 pins of the LoRA module to the ESP32

#define RST 21 //Pin de reset du module LORA
#define RX 18  //Pin RX du module LORA
#define TX 19  //Pin TX du module LORA

And We used the serial port 2 (baud 57600) of the ESP32 to communicate with the RN2483

rn2xx3 lora(Serial2);

To use the simple radio communication. you have to send with the serial monitor connected to your PC this commande (radio tx "hexa_msg")
To receive radio communication, you only have to listene on the serail port 2 All the RN2483 command lines end with "\r\n"

void initialize_radio()
{
  pinMode(RESET, OUTPUT);
  digitalWrite(RESET, LOW);
  delay(100);
  digitalWrite(RESET, HIGH); //reset the RN2483

  delay(100); //wait for the RN2xx3's startup message
  Serial2.flush();
}

void setup()
{
  Serial.begin(9600);
  Serial2.begin(57600, SERIAL_8N1, RXD2, TXD2);
  initialize_radio();
  Serial.println(Serial2.readStringUntil('\n'));
  Serial2.print("radio set pwr 14\r\n");
  Serial.println(Serial2.readStringUntil('\n'));
  Serial2.print("mac pause\r\n");
  Serial.println(Serial2.readStringUntil('\n'));
}

void loop()
{
  if(Serial2.available()) {
    Serial.println(Serial2.readStringUntil('\n'));
  }
  if (Serial.available())
  { 
    String Command = Serial.readStringUntil('\n');
    Serial.println(Command);
    Serial2.print(Command + "\r\n");
  }
}

LoRAWAN

To connect to the TTN server, you have to copy past the UEI key of the RN2483 with this command (sys get hwuei) to this line

String AppEUI = "44E53245F1200CDEEC2525661C76BA38"; //AppEUI du reseau sur TTN

Then initialze the LoRAWAN module

void initialize_LoRAWAN();

KiCAD

• The sensors are connected to an SPDT switch to commute between the two of them
• The resistor R6 is required to obtain the value of R_Alu.

• The operational amplifier (LTC1050) is used to filter and amplify the current passing through the sensors' resistance
• The amplifier must have a low offset votage
• To read the value of the gas sensor you ave to use this command

uint32_t read_aime_sensor () //Recuperation de la donnée du capteur AIME
{
  int sensor_aime_Value = analogRead(ADC_SENS);
  sensor_aime_volt=(float)sensor_aime_Value/4096*V3_3;
  float R_capteur=(1+R3/R2)*R1*V3_3/sensor_aime_volt-R1-R5; //formule justifiée en TD
  return R_capteur;
}

• The gas sensor works at least at a temperature of 200°C, so we control the R_poly heater with a PWM from the ESP32, and correct the system error with a PID.
• the resistor R4 is to define the current of the transistor surce (Is = beta * Ib)
• You have to define (a) and (b) of the temparture sensor

int a; //
int b; // R_aluminium = a * T(Kelvin) + b 

float temperature () // mesure de la temperature du capteur en fonction de R aluminium
{
  float T = a*(read_r_alu()) + b;
  T = T - 273; //conversion en Celcius
  return T;
}

---

int manage_PID(int consigne, int kp, int ki, int kd) //Correcteur PID pour maintenir la temprature a 200 degrés celcius
{
  int t_2 = micros();
  float delta_t = ((float) (t_2 - t_1))/1E6
  t_1 = t_2;


  e_t = consigne - temperature();
  e_integral = e_integral + e_t * delta_t; 
  float e_D = (e_t - e_t_1) / (delta_t);
  uint8_t C = kp*e_t + ki*e_integral + kd*e_D;

  t_2 = t_1;
  e_t_1 = e_t;

  C = fabs(C);

  if(C > 255) C = 255; //Pour borner la correction entre 0 et 255
 
  return C; //Duty cycle de la PWM de commande
}

void Cmd_PWM_Poly(int duty_cycle) //Commande de la resistance de chauffe en PWM
{
  ledcWrite(ledChannel,duty_cyle);
}

• The comparator (LT071) is used to release an interrupt on the ESP32 when the sensor detect a certain gas
• We have defined a refrence voltage on the V+ whith a volatage divider R7 and R8
• If the sensor detect a gas, the sensor voltage ADC dropdown and the output LT071 will be 1

we designed the PCB.

Node-Red

For the last part, we needed an application to setup the system and a dashboard to display the sensor values. For this, we used Node-red to connect the gas sensor with the TTN server via LORAWAN communication.

The dashboard of the system

DATASHEET

you can find the datasheet HERE