Esp32 fails to read MH-Z19C sensor

Question

I'm trying to read CO2 data from a MH-Z19C sensor with an ESP32 board but I'm not getting anything. The error code from the library is 2 indicating a timeout (no data received).

Did I get the wiring wrong? I wonder if the sensor is fried ?

Library: MH-Z19 by Jonathan Dempsey

Connections:

• MH-Z19C RX to TX2 (17)
• MH-Z19C TX to RX2 (16)
• MH-Z19C VIN to Power Supply 5V
• MH-Z19C GND to Power Supply 3V

Code:

#include <SoftwareSerial.h>
#include <MHZ19.h>
#include <Wire.h>
// pin for uart reading
#define RX_PIN 16 // Rx pin which the MHZ19 Tx pin is attached to.
#define TX_PIN 17 // Tx pin which the MHZ19 Rx pin is attached to.
MHZ19 myMHZ19;
SoftwareSerial mySerial(RX_PIN, TX_PIN);
void setup() {
 Serial.begin(9600);
 // Start Co2 sensor
 mySerial.begin(9600); // (Uno example) device to MH-Z19 serial start
 myMHZ19.begin(mySerial); // *Serial(Stream) refence must be passed to library begin().
 myMHZ19.autoCalibration(); // Turn auto calibration ON (OFF autoCalibration(false))
}
void loop() {
 // Wait a few seconds between measurements.
 delay(5000);
 int CO2;
 // Request CO2 (as ppm)
 CO2 = myMHZ19.getCO2();
 Serial.println(String(CO2) + " ppm");
 if (myMHZ19.errorCode != RESULT_OK) {
 Serial.print("Failed to receive CO2 value: ");
 Serial.println(myMHZ19.errorCode);
 }
}

backwards wiring esp32 power supply circuit

• 6v6gt: It is too difficult to follow your wiring in those pictures. A schematic diagram would be much better. You have mentioned a 3.3v and a 5v supply. Do these share a common ground?
• hcheung: It is unclear how the GND are connected between the boards. It will be better to have a schematic than those pictures.
• Adam Cherti: ok edited. note that the board is powered with USB while the sensor is powered by a power supply module.
• DrG: I would connect the esp gnd to the z19c gnd.
• hcheung: It means connect PIN1 of ESP32S(GND) to pin2 of of Z19C(GND), basic 101 electronics.

Answer 1

This is not a Winsen Mh-z19 sensor (or any clone following it's specs) so you won't be able to read data using a mhz19 library. Most probably it's a HC8 sensor and someone would have to rewrite library to get data from it. Here are specs: https://pcus.ru/download/hc8.pdf and some more info: https://spezifisch.codeberg.page/posts/2022-08-23/co2-sensor-reverse-engineering/

• Adam Cherti: how do you know it's not mh-z19?