Integrate WiFi LoRA V2 with SCD41 CO2 sensor

#1

I connect the WiFi LoRa32 V2 to SCD41 CO2 sensor from Sensirion via I2C bus. (https://github.com/Sensirion/arduino-i2c-scd4x)

I can display the CO2, temp and humidity sensor reading via COM port on PC. However, when I tried to display the reading on local OLED (SSD1306) display, there seems to have some conflict. Once I initialize the OLED and display some text, I can no longer communicate with the SCD41 via I2C. I always got communication error message. What is the I2C address for the OLED of WiFi LoRa32? Any suggestions to resolve the problem?

#2

The IIC address of the display is 0x3C.

#3

Thanks. (BTW, I search online and found the SSD1306 OLED driver is -write address is 0x78
-read address is 0x79 for ESP32. https://embeddeddiaries.com/esp32-oled-sd1306-i2c-interface/, not sure who is right?)

The I2C address of SCD41 is 0x62. So the problem is probably not due to address conflict.

Any suggestion how to resolve this problem?

#4

You can use this example to view the IIC address of the display:

#5

What are the pins used by your sensor?

#6

Hi Shaffer:

Thank you very much for the utility code. It is very helpful.
I modified the code to use wire1.xxxx functions to communicate with sensor and wire.xxxx functions to communicate with OLED display, everything works now. Thank you very much for your help!!

#7

Hi Peter,

I’m interested in setting up a similar system. Could you please share your code?

Thanks!

#8

Here is the code:

// SCD41_CO2_V201
// Add local OLED display of sensor readdings & battery voltage
// Add LED lights to indicate reading period
// SDA(GPIO21) & SCL(GPIO#22) are for I2C to SCD41
// GPIO#21 is set to (LOW)initially to connect Vbat to GPIO#37 (ADC1_1)
// After Vbat is measured in the setup, GPIO#21 is reconfigured for I2C to connect to SCD41
//
// SDA_OLED (GPIO#04) & SCL(GPIO#15)are for I2C to OLED display
// use wire1.xxxx functions to communicate with SCD41
// and wire.xxxx function to communicate with Oled SSD1306
//
// SCD41_CO2_v200
// Example8_SCD4x_BLE_gadget_with_RHT.ino
// This code is included in Sensirion’s Arduino Snippets
// It worked right away with WiFi LoRa32 V2 board using iOS apps Myambience
// Check https://github.com/Sensirion/arduino-snippets for the most recent version.

#include “esp_timer.h”
#include “Sensirion_GadgetBle_Lib.h”
#include “heltec.h”
#include <Wire.h>

#define Fbattery 3700 //The default battery is 3700mv when the battery is fully charged.

//float XS = 0.00225; //The returned reading is multiplied by this XS to get the battery voltage.
float XS = 0.00225*1.354; // multiply by a factor of 1.354 to factor in the load from I2C bus SDA line
uint16_t MUL = 1000;
uint16_t MMUL = 100;
uint16_t c;

// SCD41
const int16_t SCD_ADDRESS = 0x62;

// GadgetBle workflow
static int64_t lastMmntTime = 0;
static int mmntIntervalUs = 5000000;
GadgetBle gadgetBle = GadgetBle(GadgetBle::DataType::T_RH_CO2);

void setup() {
// sdetup to check battery voltage
// Heltec.begin(true /DisplayEnable Enable/, false /LoRa Enable/, true /Serial Enable/);

Serial.begin(115200);
// wait for serial connection from PC
// comment the following line if you’d like the output
// without waiting for the interface being ready
while(!Serial);

Serial.print("SCD41_CO2_V201 device ID = ");
// Initialize the GadgetBle Library
gadgetBle.begin();
Serial.println(gadgetBle.getDeviceIdString());
Serial.print("Vbat = ");
// setup & measure Vbat
pinMode(21,OUTPUT); // setup GPIO#21 to tuern on connection from Vbat to ADC1_1 (pin#37)
pinMode(LED_BUILTIN, OUTPUT);
digitalWrite(21,LOW);
adcAttachPin(13);
analogSetClockDiv(255); // 1338mS
delay(1000);
c = analogRead(37)XSMUL;
// Serial.println(analogRead(37));
Serial.println©;

// init I2C
// Heltec.begin(true, false, true);
Wire.begin(SDA_OLED, SCL_OLED); //Scan OLED’s I2C address via I2C0
Wire1.begin(SDA, SCL); //If there have other device on I2C1, scan the device address via I2C1
// Wire.begin();

// wait until sensors are ready, > 1000 ms according to datasheet
delay(1000);

// initialize OLED display
Heltec.display->init();
Heltec.display->flipScreenVertically();
Heltec.display->setFont(ArialMT_Plain_16);
Heltec.display->clear();

Heltec.display->drawString(8, 0, "SCD41-V201");
Heltec.display->drawString(12, 45, "Renata LLC");
Heltec.display->display();

delay(3000);
Heltec.display->clear(); 
Heltec.display->drawString(0, 10, "Vbat=");
Heltec.display->drawString(50, 10, (String)c);
Heltec.display->drawString(90, 10, "mV");
if (c < 3200)
  Heltec.display->drawString(0, 50, "Low Battery");

Heltec.display->display();

// output format
Serial.println(“Temp(F)\tRH(%)\tCO2(ppm)”);
delay(5000);

// start scd measurement in periodic mode, will update every 2 s
Wire1.beginTransmission(SCD_ADDRESS);
Wire1.write(0x21);
Wire1.write(0xb1);
Wire1.endTransmission();

// wait for first measurement to be finished
delay(2000);
}

void loop() {
if (esp_timer_get_time() - lastMmntTime >= mmntIntervalUs) {
measure_and_report();
}

gadgetBle.handleEvents();
delay(3);
}

void measure_and_report() {
float co2, temperature, humidity, temp1;
uint8_t data[12], counter;

// send read data command
Wire1.beginTransmission(SCD_ADDRESS);
Wire1.write(0xec);
Wire1.write(0x05);
Wire1.endTransmission();

// read measurement data: 2 bytes co2, 1 byte CRC,
// 2 bytes T, 1 byte CRC, 2 bytes RH, 1 byte CRC,
// 2 bytes sensor status, 1 byte CRC
// stop reading after 12 bytes (not used)
// other data like ASC not included
Wire1.requestFrom(SCD_ADDRESS, 12);
counter = 0;
while (Wire1.available()) {
data[counter++] = Wire1.read();
}

// floating point conversion according to datasheet
co2 = (float)((uint16_t)data[0] << 8 | data[1]);
// convert T in deg C & F
temperature = -45 + 175 * (float)((uint16_t)data[3] << 8 | data[4]) / 65536;
temp1 = ((-45 + 175 * (float)((uint16_t)data[3] << 8 | data[4]) / 65536)/5)*9 + 32;
// convert RH in %
humidity = 100 * (float)((uint16_t)data[6] << 8 | data[7]) / 65536;

Serial.print(temp1);
Serial.print(" \t");
Serial.print(humidity);
Serial.print("\t");
Serial.print(co2);
Serial.println();

gadgetBle.writeCO2(co2);
gadgetBle.writeTemperature(temperature);
gadgetBle.writeHumidity(humidity);

gadgetBle.commit();
lastMmntTime = esp_timer_get_time();

digitalWrite(LED_BUILTIN,HIGH);

// display in OLED
Heltec.display->clear();
Heltec.display->setFont(ArialMT_Plain_24);
Heltec.display->drawString(5, 0, String(int(co2), DEC) + " ppm");
Heltec.display->setFont(ArialMT_Plain_16);
// Heltec.display->drawString(15, 45, “Vbat " + (String)c);
Heltec.display->drawString(15, 40, String(int(temp1),DEC) + " F”);
Heltec.display->drawString(65, 40, String(int(humidity),DEC) + " %");
Heltec.display->display();
delay(150);
digitalWrite(LED_BUILTIN,LOW);
}