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https://github.com/sigmasternchen/MH-Z-CO2-Sensors
synced 2025-03-15 06:38:55 +00:00
Added a modified version which shows the CO2 measurements on a LCD.
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145
MH-Z19B-LCD/MH-Z19B.ino
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145
MH-Z19B-LCD/MH-Z19B.ino
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#include <SoftwareSerial.h>
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// include the library code:
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#include <LiquidCrystal.h>
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// initialize the library with the numbers of the interface pins
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LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
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SoftwareSerial co2Serial(7, 6); // define MH-Z19 RX TX
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unsigned long startTime = millis();
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void setup() {
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Serial.begin(9600);
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co2Serial.begin(9600);
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pinMode(9, INPUT);
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// set up the LCD's number of columns and rows:
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lcd.begin(16, 2);
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lcd.print("CO2 heating up");
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lcd.setCursor(4, 1);
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lcd.print("seconds left");
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for (int seconds = 180; seconds > 0; seconds--) {
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lcd.setCursor(0, 1);
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lcd.print(" "); // clear timer
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lcd.setCursor(0, 1);
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lcd.print(seconds);
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delay(1000);
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}
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lcd.clear();
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lcd.setCursor(0, 0);
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lcd.print("CO2 Air Quality");
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}
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void loop() {
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Serial.println("------------------------------");
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Serial.print("Time from start: ");
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Serial.print((millis() - startTime) / 1000);
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Serial.println(" s");
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int ppm_uart = readCO2UART();
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int ppm_pwm = readCO2PWM();
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// TODO: just clear second line?
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lcd.clear();
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lcd.setCursor(0, 0);
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lcd.print("CO2 Air Quality");
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lcd.setCursor(0, 1);
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lcd.print("PPM: ");
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lcd.setCursor(5, 1);
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lcd.print(ppm_pwm);
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lcd.setCursor(10, 1);
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lcd.print("|");
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lcd.setCursor(12, 1);
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lcd.print(ppm_uart);
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delay(5000);
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}
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int readCO2UART() {
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byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
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byte response[9]; // for answer
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Serial.println("Sending CO2 request...");
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co2Serial.write(cmd, 9); //request PPM CO2
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// clear the buffer
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memset(response, 0, 9);
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int i = 0;
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while (co2Serial.available() == 0) {
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// Serial.print("Waiting for response ");
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// Serial.print(i);
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// Serial.println(" s");
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delay(1000);
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i++;
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}
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if (co2Serial.available() > 0) {
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co2Serial.readBytes(response, 9);
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}
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// print out the response in hexa
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for (int i = 0; i < 9; i++) {
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Serial.print(String(response[i], HEX));
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Serial.print(" ");
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}
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Serial.println("");
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// checksum
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byte check = getCheckSum(response);
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if (response[8] != check) {
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Serial.println("Checksum not OK!");
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Serial.print("Received: ");
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Serial.println(response[8]);
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Serial.print("Should be: ");
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Serial.println(check);
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}
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// ppm
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int ppm_uart = 256 * (int)response[2] + response[3];
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Serial.print("PPM UART: ");
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Serial.println(ppm_uart);
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// temp
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byte temp = response[4] - 40;
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Serial.print("Temperature? ");
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Serial.println(temp);
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// status
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byte status = response[5];
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Serial.print("Status? ");
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Serial.println(status);
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if (status == 0x40) {
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Serial.println("Status OK");
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}
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return ppm_uart;
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}
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byte getCheckSum(char *packet) {
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byte i;
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unsigned char checksum = 0;
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for (i = 1; i < 8; i++) {
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checksum += packet[i];
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}
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checksum = 0xff - checksum;
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checksum += 1;
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return checksum;
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}
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int readCO2PWM() {
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unsigned long th, tl, ppm_pwm = 0;
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do {
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th = pulseIn(9, HIGH, 1004000) / 1000;
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tl = 1004 - th;
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ppm_pwm = 5000 * (th - 2) / (th + tl - 4);
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} while (th == 0);
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Serial.print("PPM PWM: ");
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Serial.println(ppm_pwm);
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return ppm_pwm;
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}
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