Published May 9, 2021 © GPL3+

Incorporating GPS and solar-power to environmental sensors

We developed a solar-powered sensing device, able to determine and track key environmental parameters in real time.

AdvancedWork in progress905

Incorporating GPS and solar-power to environmental sensors

Things used in this project

Hardware components

Adafruit Medium 6V 2W Solar panel - 2.0 Watt

Sensirion SCD30 CO2 sensor module

DFRobot Gravity: Analog Capacitive Soil Moisture Sensor- Corrosion Resistant

Seeed Studio Soil Moisture & Temperature Sensor

Rechargeable Battery, Lithium Ion

Adafruit Solar Lithium Ion/Polymer charger

Seeed Studio Grove - GPS

Software apps and online services

Arduino IDE

Story

1. Synopsis

The determination of environmental factors such as the humidity, light intensity or gas concentrations is essential in a wide range of applications, including crop production and field characterisation. However, in large-scale applications, where extensive lands are involved, the location data is also necessary to allow a mapping of these parameters at different positions.

To allow the monitoring of different environmental parameters whilst allowing their mapping in field applications, we designed a device that included a solar-powered Wio Terminal, where multiple sensors and a GPS device had been incorporated. The lcd screen on the Wio Terminal, not only allowed a display of the results, but it could also be used to show in a map the position where the different measurements had been taken. To power this project, we employed a solar panel and a rechargeable lithium-ion battery, that could be connected with the Wio Terminal.

2. Design of the device

For the complete determination of environmental parameters, we included 4 different sensors; SCD30, analog UV sensor, Capacitive moisture sensor and temperature sensor. The SCD30 device could be used for the simultaneous determination of air humidity, temperature and CO2 concentrations. As such, it provided a good characterisation of the field conditions. To complement this information, we included a UV sensor, which provided an idea of the light intensity, and two devices for the determination of soil temperature and humidity. These data was displayed on the Wio Terminal screen and automatically updated in the case of position or environmental sensors. In the case of soil measurements, the measurements were updated once the push button had been pressed, to avoid taking measurements that were not related with the soil status. The sensor interface using the Wio Terminal screen can be seen below.

Sensors employed within the present project for the measurement of environmental parameters (left). Display on the Wio Terminal showing the data measured by the sensors (right).

The power needed to run this project was provided by a Solar panel, obtained from Adafruit. This solar panel could be combined with a battery to allow a continuous measurement of the different parameters. As such, it could be incorporated for field applications, to determine different environmental parameters and record them. A complete view of the device we developed can be observed below.

Picture of the full device developed including the sensors, batteries, and solar charger.

3. Wio Terminal interface

The interface we designed made use of the three buttons on the Wio Terminal device, displaying a different screen on each button. When the system is set on the first button, the device shows the current data as measured by the different sensors and the GPS. After pressing the blue push button on the device, the sensor recorded the current data, including the location of the user, that can be later observed in the map. This position in the map could indicate the user the places where the measurements had been taken.

When the second button was pressed, the user could see the recorded data, and soil measurements were taken. Up to 10 different measurements could be taken and recorded by the user, and the number of each measurement is indicated on the screen as seen below. The position where each sample measurement had been taken is also indicated when the user switches to the third menu, with the map display.

Finally, on the third menu, a map of the field where the measurements are being taken can be observed. This map had to be downloaded by the user before conducting the measurements, and uploaded the the Wio Terminal following the tutorials by Seeed Studio. The images can be taken from different sources such as goolge maps, and the limits of the longitude and latitude have to be recorded and added to the programme to allow the correct positioning of of the coloured circle. The current position of the user was indicated by a red circle while the past position indicated in the second menu could be seen in blue. These three different display options can be seen below.

Pictures of the three different displays that can be used within the present project for the measurement of the environmental parameters.

4. Code

The code used for the display can be seen below. This code was based on previously reported projects on gps devices using Wio Terminals like this one from Seeed.

Code used for the present project

#include <Seeed_FS.h>
#include "TFT_eSPI.h"
#include <SPI.h>
#include <SD/Seeed_SD.h>
#include <Wire.h>
#include "SparkFun_SCD30_Arduino_Library.h"
#include <RawImage.h>
#include <SoftwareSerial.h>
#include <TinyGPS++.h>
    
//We define the class types for the different sensors we will be employing throughout the programme (gps, and light and gas sensors)
SCD30 airSensor;
TinyGPSPlus gps;

//We also define the class types for the display of objects in the screen
TFT_eSPI tft;

//We indicate the pins for the GPS device
SoftwareSerial mySerial(2, 3);

//Here we define the variables employed in the code
double dist_LAT = 34.9722899, dist_LONG = 138.3868869;
String p_hour, p_lat, p_lng, p_alt, p_sat, p_date;
String p_my_speed, p_my_course, p_dist_dTo, p_dist_cTo;
String pdist_LAT, pdist_LONG;
String sdist_LAT = String(dist_LAT);
String sdist_LONG = String(dist_LONG);
String Date[10], Dat;
int menu = 1;
byte RX1;
uint8_t Cut = 78;
char buffer[64], Data [64], Message;   // buffer array for data receive over serial port
int count=0;                           // counter for buffer array
double Val1, Val2;
int count3 = 0;
int y, Latc, Lonc, i, j, Lat[10], val1, val2, val3, s, p, z, tUV, tlux;
float tTemp, tHum, tCO2, Buff;
uint8_t val[2];
double LatLim1, LatLim2, LonLim1, LonLim2;
String N_Stemp, p_Temp, p_Stemp, N_mois, N_EC, N_CO2, N_Hum, N_Temp, p_STemp, p_mois, p_EC, p_CO2, p_Hum;
int Log_f = 0;
String N_date, hour0;
unsigned long p_time;
int N_y, N_m, N_d;
String hr1, min1, sec1;
String F_name, N_Mois, p_Mois, nhour0[5];
bool sd;
float tEC, tMois, tStemp;
int l, Lng[10];
String N_lux, N_UV, p_lux, p_UV;
int Num = 0;
int k = 1;
float lux[10], Temp[10], Hum[10], CO2[10], Stemp[10], EC[10], Mois[10],  UV[10];
String Longitude[10], Latitude[10], Alt[10], Sat[10];
static const int MAX_SATELLITES = 40;
float uUV, ulux, uCO2, uSTemp, uHum, uTemp, uEC, uMois;

//We will initialise the custom types from the TinyGPS++ library, to determinethe position, elevation, and number of satellites
TinyGPSCustom ExtLat(gps, "GPGGA", 3); 
TinyGPSCustom ExtLng(gps, "GPGGA", 5); 
TinyGPSCustom totalGPGSVMessages(gps, "GPGSV", 1); 
TinyGPSCustom messageNumber(gps, "GPGSV", 2);     
TinyGPSCustom satsInView(gps, "GPGSV", 3);         
TinyGPSCustom satNumber[4]; // to be initialized later
TinyGPSCustom elevation[4];
TinyGPSCustom azimuth[4];
TinyGPSCustom snr[4];

//Define the addresses of the soil probe device for the determination of Temperature, conductivity and moisture
const byte Addr[] = {0x01, 0x04, 0x00, 0x00, 0x00, 0x03, 0xB0, 0x0B};

struct
{
  bool active;
  int elevation;
  int azimuth;
  int snr;
  int dsp;
} sats[MAX_SATELLITES];

    volatile uint32_t newlines = 0UL;
    
    static void handleRxChar( uint8_t c )
    {
      if (c == '\n')
        newlines++;
    }

void setup() {

  mySerial.begin(9600);
  tft.begin();
  tft.setRotation(3);

//This command initialises the SD device included in the Wio terminal
        if (!SD.begin(SDCARD_SS_PIN, SDCARD_SPI)) {
   sd = false;
   }
       else {
          SerialUSB.println("initialization done.");
//First, we need to initialise the devices that will be used on this project, and the Serial communications
  Wire.begin();
  airSensor.begin();
  Serial.begin(9600);
        sd = true;
    }
        for (int i=0; i<4; ++i)
    {
      satNumber[i].begin(gps, "GPGSV", 4 + 4 * i); // offsets 4, 8, 12, 16
      elevation[i].begin(gps, "GPGSV", 5 + 4 * i); // offsets 5, 9, 13, 17
      azimuth[i].begin(gps, "GPGSV", 6 + 4 * i); // offsets 6, 10, 14, 18
      snr[i].begin(gps, "GPGSV", 7 + 4 * i); // offsets 7, 11, 15, 19
    }

//We set the initial values for some of the variables employed throughout the loop 
p = 0;
j = 0;
p = 0;
s = 1;
Num = 0;
count = 0;

//These variables indicate the minimum and maximum values of latitude and longitude on the displayed map 
LatLim1 = 50;
LatLim2 = 55;
LonLim1 = 50;
LonLim2 = 60;

//These commands set the pin used on the programme, for the measurement of UV light intensity as input pins
pinMode (A7, INPUT);
pinMode (A4, INPUT);
pinMode (A6, INPUT);

//These commands initialise the push buttons in the Wio Terminal
pinMode(WIO_5S_PRESS, INPUT_PULLUP);
pinMode(WIO_KEY_A, INPUT_PULLUP);
pinMode(WIO_KEY_B, INPUT_PULLUP);
pinMode(WIO_KEY_C, INPUT_PULLUP);
pinMode(WIO_5S_LEFT, INPUT_PULLUP);
pinMode(WIO_5S_RIGHT, INPUT_PULLUP);
}

void loop() {

//These commands take the measurements from the SCD30 sensor
if (airSensor.dataAvailable())
{
tTemp = airSensor.getTemperature();
tHum = airSensor.getHumidity();
tCO2 = airSensor.getCO2(); 
}

//Since the UV sensor has an analog output, we read the signals form the pins where it has been connected
for (i=0; i<10; i++){
tUV = tUV + analogRead (A7);
}

tUV = tUV/10;

//We convert the environmental measurements to string variables by using the following command 
//These will be the variables displayed on the screen
N_UV = String(tUV);
N_Temp = String(tTemp);
N_Hum = String(tHum);
N_CO2 = String(tCO2);
  
long N_mjd;

//Command to save the data from the sensors and the GPS to a SD card. This function will be executed every 6s
while (mySerial.available() > 0) {
char c = mySerial.read();
gps.encode(c);
}

//calculate the latitude and longitude values, and transform it to a string for the display
    double lat0 = gps.location.lat();
    double lat1 = (lat0 -int(lat0))*60;
    double lat2 = (lat1 - int(lat1))*60;
    String lat3 = String(int(lat0))+':' + String(int(lat1))+':'+String(lat2) + ' ' + String(ExtLat.value());
    double lng0 = gps.location.lng();
    double lng1 = (lng0 -int(lng0))*60;
    double lng2 = (lng1 - int(lng1))*60;
    String lng3 = String(int(lng0))+':' + String(int(lng1))+':'+String(lng2) + ' ' + String(ExtLng.value());

//calculate the time and transform it to a string for the display
    int hr = gps.time.hour()+9;
    if (hr>24) hr -= 24;
    String hr0 = '0'+String(hr);
     hr1 = hr0.substring(hr0.length()-2); 
    String min0 = '0'+String(gps.time.minute());
     min1 = min0.substring(min0.length()-2); 
    String sec0 = '0'+String(gps.time.second());
     sec1 = sec0.substring(sec0.length()-2);
    hour0 =  hr1+':'+min1+':'+sec1;

//Calculate date and transform it to a string for the display
    if (gps.date.isUpdated()) {
        int y = gps.date.year();
        int m = gps.date.month();
        int d = gps.date.day();
        if(m<3){y--; m+=12;}
        long mjd = int(361.7015*y)+int(y/400)-int(y/100)+int(30.59*(m-2))+d-678912;
        if(gps.time.hour()>14) 
            N_mjd = 58580+(mjd-51412);
        else
            N_mjd = 58579+(mjd-51412);
        long n = N_mjd+678881;
        long a = 4*n+3+3*(4*(n+1)/146097+1);
        long b = 5*((a % 1461)/4)+2;
        N_y = int(a/1461);
        N_m = int(b/153+3);
        N_d = int((b % 153)/5+1);
        if (N_m>12){N_y++; N_m-=12;}
        N_date = String(N_y)+'/'+('0'+String(N_m)).substring(('0'+String(N_m)).length()-2)+'/'+('0'+String(N_d)).substring(('0'+String(N_d)).length()-2);
    }

//When the user presses the pushbutton on the Wio terminal, the RS485 communications are triggered for the soil measurements
//The location where the measurements have been taken is also fixed and displayed on the Wio terminal screen
if (digitalRead(WIO_5S_PRESS) == LOW) {

//The Soil measurements will only take place if the Wio terminal is on the data display mode
if (menu ==1){  

//This code saves the current position at the moment of initialising the measurement, for display in the lcd screen
lng0 = lng0*100;
Lng [p] = map(lng0, LonLim1, LonLim2, 0, 240);
Lat [p] = map (lat0, LatLim1, LatLim2, 0, 320);
lng0 = lng0/100;

//We perform the soil temperature and moisture measurements
for (i=0;i<10;i++){
tStemp = tStemp + analogRead (A4);
tMois = tMois + analogRead (A6);
}
tStemp = tStemp/10;
tStemp = tStemp*(-0.0826) + 108.65;
tMois = tMois/10;
tMois = tMois*5/1024;

N_Stemp = String (tStemp);
N_Mois = String (tMois);

Date[p] =  N_date;
nhour0[p] = hour0;
Alt[p] = String(gps.altitude.meters());
Sat[p] = String(gps.satellites.value());
Temp[p] = tTemp;
Hum[p] = tHum;
CO2[p] = tCO2;
UV[p] = tUV;
Stemp[p] = tStemp;
Mois[p] = tMois;
Latitude[p] = lat3;
Longitude[p] = lng3;

//These lines determine the number of points that will be displayed on the map screen
p++;
count++;
if (p>10){
  p = 0;
  count = 10;
}

//The value of s determines the first time that the titles of the measurements are displayed on the Wio Terminal screen
s = 1;  

  }
}

//This condition will show the value of the measurements
if (menu == 1){
  
//The first time that the menu is displayed, we need to initialise the screen colour and the measurement titles
    if (s==1){
    tft.fillScreen (TFT_BLACK);
    tft.setTextSize(3);
    tft.drawString("GPS",50,3);
    tft.drawString("SCD30",30,150);
    tft.drawString("Soil",200,3);
    tft.drawString("Light",200,150);
    tft.setTextSize(1);
    tft.drawString("Date",20,33);
    tft.drawString("Time",20,53);
    tft.drawString("LAT",20,70);
    tft.drawString("LONG",20,87);
    tft.drawString("ALT (m)",20,107);
    tft.drawString("Satellites",20,127);
    tft.drawString("Temp (oC)",20,180);
    tft.drawString("Hum (%)",20,200);
    tft.drawString("CO2 (ppm)",20,220);
    tft.drawString("Temp (oC)",180,33);
    tft.drawString("Moisture (V)",180,53);
    tft.drawString("UV ",180,180);
    }

    if (N_date != p_date || s == 1) {    //Displays the date
      tft.fillRect(50,33,70,20,TFT_BLACK);
      tft.drawString(N_date,50,33);
      p_date = N_date;
    }
    
    if (hour0 != p_hour || s == 1) {    //Displays the time
      tft.fillRect(50,53,100,16,TFT_BLACK);
      tft.drawString(hour0,50,53);
      p_hour = hour0;
    }
    
    if (lat3 != p_lat || s == 1) {      //Displays the latitude
      tft.fillRect(50,70,110,10,TFT_BLACK);
      tft.drawString(lat3,50,70);
      p_lat = lat3;
    }
    
    if (lng3 != p_lng || s == 1) {      //Displays the longitude
      tft.fillRect(50,90,87,10,TFT_BLACK);
      tft.drawString(lng3,50,90);
      p_lng = lng3;
    }

    if (String(gps.altitude.meters()) != p_alt || s == 1) { //Displays the altitude
      tft.fillRect(70,107,107,10,TFT_BLACK);
      tft.drawString(String(gps.altitude.meters()),70,107);
      p_alt = String(gps.altitude.meters());
    }
    
    if (String(gps.satellites.value()) != p_sat || s == 1) {  //Displays the number of satellites
      tft.fillRect(90,127,110,10, TFT_BLACK);
      tft.drawString(String(gps.satellites.value()),90,127);
      p_sat = String(gps.satellites.value());
    }
    
    tft.fillRect(0,140,320,2,TFT_YELLOW);
    tft.fillRect(160,0,2,240,TFT_YELLOW);


if (N_Temp != p_Temp || s == 1){ //Displays the environmental temperature
    tft.fillRect(80,180,32,16,TFT_BLACK);
    tft.drawString(N_Temp, 80, 180);
    p_Temp = N_Temp;
}

if (N_Hum != p_Hum || s == 1){ //Displays the air humidity
    tft.fillRect(90,200,32,16,TFT_BLACK);
    tft.drawString(N_Hum, 80, 200);
    p_Hum = N_Hum;
}

if (N_CO2 != p_CO2 || s == 1){ //Displays the concentration of CO2
    tft.fillRect(80,220,32,16,TFT_BLACK);
    tft.drawString(N_CO2, 80, 220); 
    p_CO2 = N_CO2;
}

if (N_Stemp != p_Stemp || s == 1){ //Displays the temperature in soil
    tft.fillRect(240,33,32,16,TFT_BLACK);
    tft.drawString(N_Stemp, 240, 33);
    p_Stemp = N_Stemp;
}

if (N_Mois != p_Mois || s == 1){ //Displays the volumetric soil water content
    tft.fillRect(270,53,32,16,TFT_BLACK);
    tft.drawString(N_Mois, 260, 53); 
    p_Mois = N_Mois;
}

if (N_UV != p_UV || s == 1){ //Displays the intensity from the UV sensor
    tft.fillRect(200,180,80,16,TFT_BLACK);
    tft.drawString(N_UV, 200, 180); 
    p_UV = N_UV;
}

s = 0;
}

if (menu == 2){
  
   if (digitalRead(WIO_5S_RIGHT) == LOW) {
      Num = Num + 1;
      l = 1;
   }
   if (digitalRead(WIO_5S_LEFT) == LOW) {
      Num = Num - 1;
      l = 1;
   }

   if (Num<0){
   Num = count; 
   }

   if (Num>count-1){
   Num = 0; 
   }

  Dat = String(Num);
  
if (l == 1){

    tft.fillScreen (TFT_BLACK);
    tft.setTextSize(3);
    tft.drawString("GPS",50,3);
    tft.drawString("SCD30",30,150);
    tft.drawString("Soil",170,3);
    tft.drawString("Light",200,150);
    tft.setTextColor(TFT_YELLOW);
    tft.drawString("Sample",170,210);
    tft.drawString(Dat,285,210);
    tft.setTextColor(TFT_WHITE);
    tft.setTextSize(1);
    tft.drawString("Date",20,33);
    tft.drawString("Time",20,53);
    tft.drawString("LAT",20,70);
    tft.drawString("LONG",20,87);
    tft.drawString("ALT (m)",20,107);
    tft.drawString("Satellites",20,127);
    tft.drawString("Temp (oC)",20,180);
    tft.drawString("Hum (%)",20,200);
    tft.drawString("CO2 (ppm)",20,220);
    tft.drawString("Temp (oC)",180,33);
    tft.drawString("Moisture (%)",180,53);
    tft.drawString("UV: ",180,180);

    tft.fillRect(0,140,320,2,TFT_YELLOW);
    tft.fillRect(160,0,2,240,TFT_YELLOW);

    Dat = String (Date[Num]);
    //Date
    tft.drawString(Dat,50,33);

    Dat = String (nhour0[Num]);
    tft.drawString(Dat,50,53);
      p_hour = hour0;

    Dat = String (Latitude[Num]);
      tft.drawString(Dat,50,70);

    Dat = String (Longitude[Num]);
      tft.drawString(Dat,50,90);

    Dat = Alt[Num];
      tft.drawString(Dat,70,107);

    Dat = Sat[Num];
      tft.drawString(Dat,90,127);

    Dat = String(Temp[Num]);
    tft.drawString(Dat, 80, 180);

    Dat = String(Hum[Num]);
    tft.drawString(Dat, 50, 200);

    Dat = String(CO2[Num]);
    tft.drawString(Dat, 80, 220); 

    Dat = String(Stemp[Num]);
    tft.drawString(Dat, 240, 33);

    Dat = String(Mois[Num]);
    tft.drawString(Dat, 260, 53);
   
    Dat = String(UV [Num]);
    tft.drawString(Dat, 240, 180); 
}
  l = 0;
  
}

//We initialise the map display, to see our current position and the places where measurements have been taken
if (menu == 3){
  delay (100);
if (k==1){

//Command to display the map, stored in the SD card memory
drawImage<uint16_t>("map.bmp", 0, 0);

//This function takes the coordinates,and the maximum coordinates indicated by the user to map them and show them on the screen
lng0 = lng0*100;
Latc = map (lat0, LatLim1, LatLim2, 0, 320);
Lonc = map (lng0, LonLim1, LonLim2, 0, 240);
lng0 = lng0/100;

if (l==1){
//We draw a green circle at the current position
tft.fillCircle(Latc, Lonc, 4, TFT_RED);
}

if (l==0){
//We draw a green circle at a past position (only if we are on menu 2)
tft.fillCircle(Lat[Num], Lng[Num], 4, TFT_BLUE);  
}

delay (100);
}
k = 0;
}


//This codes are used to detect the input from the push buttons and change between the menus
   if (digitalRead(WIO_KEY_C) == LOW) {
    menu = 1;
    l = 1;
    s = 1;
    k = 1;
   }
   else if (digitalRead(WIO_KEY_B) == LOW) {
    menu = 2;
    s = 1;
    l = 1;
    k = 1;
   }
   else if (digitalRead(WIO_KEY_A) == LOW) {
   menu = 3;
   s = 1;
   k = 1;
   }
   
  delay (100);
}