Use Different I2C Pins

Q&A Forum › Category: ESP32 › Use Different I2C Pins

David Fenner asked 7 days ago

Hi readers.
I am trying to connect two sensors SI7021 and HTU21d to a ESP32_6 mini therefore I need to assign I2C as my understanding is that it doesn’t have default I2C pins like the ESP32 does.
So my first project with this board was using a BME280 sensor using the information supplied by Rui Santos. Use Different I2C Pins with ESP32 (change default I2C pins)

ESP32 I2C Communication: Set Pins, Multiple Bus Interfaces and Peripherals (Arduino IDE)

I am a bit lost now when I look at the respective Adafrult CPP files . Therefore I would appreciate some expert assistance in how I use the information in the CPP files.
So I know the commands to use in my configuration/ setup of my respective sketchs

Question Tags: Use Different I2C Pins ESP32 6 mini

8 Answers

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Sara Santos Staff answered 5 days ago

Hi.
You don’t need to modify any library files.
In the tutorial, we’re just taking a look at the library files to see that the only way to use custom pins with the library is to use a TwoWire instance.

You can use this code as a starting point: https://raw.githubusercontent.com/RuiSantosdotme/Random-Nerd-Tutorials/master/Projects/ESP32/I2C/ESP32_BME280_Set_I2C_Pins.ino

You can adjust the pins you want to use in these lines:

#define I2C_SDA 33
#define I2C_SCL 32

Regards,
Sara

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David Fenner answered 5 days ago

Hi Sara
Thank you for your reply. I am using your example as a starting point as you suggested, however I have run into a problem.
Below is the error I am being presented with followed by my sketch could you comment on where I am going wrong.

C:\Users\Me\Documents\Arduino\ESP32_6_HTU21D\ESP32_6_HTU21D.ino: In function ‘void setup()’: C:\Users\Me\Documents\Arduino\ESP32_6_HTU21D\ESP32_6_HTU21D.ino:15:19: error: no matching function for call to ‘Adafruit_HTU21DF::begin(int, TwoWire*)’ 15 | status = htu.begin(0x40, &I2Chtu); | ~~~~~~~~~^~~~~~~~~~~~~~~ In file included from C:\Users\Me\Documents\Arduino\ESP32_6_HTU21D\ESP32_6_HTU21D.ino:2: C:\Users\Me\Documents\Arduino\libraries\Adafruit_HTU21DF_Library/Adafruit_HTU21DF.h:36:8: note: candidate: ‘bool Adafruit_HTU21DF::begin(TwoWire*)’ 36 | bool begin(TwoWire *theWire = &Wire); | ^~~~~ C:\Users\Me\Documents\Arduino\libraries\Adafruit_HTU21DF_Library/Adafruit_HTU21DF.h:36:8: note: candidate expects 1 argument, 2 provided C:\Users\Me\Documents\Arduino\ESP32_6_HTU21D\ESP32_6_HTU21D.ino:17:1: error: ‘If’ was not declared in this scope 17 | If (!status) { | ^~ exit status 1 Compilation error: no matching function for call to ‘Adafruit_HTU21DF::begin(int, TwoWire*)’

My work in progress sketch:-

#include <Wire.h>
#include “Adafruit_HTU21DF.h”
#define I2C_SDA 1
#define I2C_SCL 2

TwoWire I2Chtu = TwoWire(0);
Adafruit_HTU21DF htu;
void setup() {
Serial.begin(9600);
I2Chtu.begin(I2C_SDA, I2C_SCL, 100000);
bool status;
status = htu.begin(0x40, &I2Chtu);

If (!status) {
Serial.println(“Couldn’t find sensor!”);
while (1);
}
delay(1000);
Serial.println();
}
void loop() {
float temp = htu.readTemperature();
float rel_hum = htu.readHumidity();
Serial.print(“Temp: “); Serial.print(temp); Serial.print(” C”);
Serial.print(“\t\t”);
Serial.print(“Humidity: “); Serial.print(rel_hum); Serial.println(” \%”);
delay(500);
}

0 Vote Up Vote Down

Sara Santos Staff answered 4 days ago

Hi.

You must always take a look at the library files for the specific sensor you’re using.
If you take a look at the library file: https://github.com/adafruit/Adafruit_HTU21DF_Library/blob/master/Adafruit_HTU21DF.cpp

You’ll see that the begin method only accepts the TwoWire instance and not the I2C address. See line 45.

In this case, you need to modify this line:

status = htu.begin(0x40, &I2Chtu);

bool status = htu.begin(&I2Chtu);

Also, you have a capitalized If statement. It should be if.

I hope this helps.

Let me know if you can make it work.

Regards,

Sara

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David Fenner answered 4 days ago

Hi Sara,
Thank you, your fix corrected my problem.
If I may take a bit more of your time I do have a few further questions on this topic:-

Could you confirm whether the following two code snippets are the same:-
Adafruit_HTU21DF sensor;
Adafruit_Si7021 sensor = sensor ();
I can see the point yore were making regarding the following items in the library files:-
bool Adafruit_BME280::begin(uint8_t addr, TwoWire *theWire) {
bool Adafruit_HTU21DF::begin(TwoWire *theWire) {

However, on my finial sensor a si7021 the sensor Adafruit_Si7021 library file shows:
Adafruit_Si7021::Adafruit_Si7021(TwoWire *theWire) {
Could you provide an example to work with for this statement like you did with the HTU21D. My work in progress sketch is blow:-
#include “Adafruit_Si7021.h”
bool enableHeater = false;
uint8_t loopCnt = 0;
#define I2C_SDA 1
#define I2C_SCL 2
TwoWire I2Csensor = TwoWire(0);
//Adafruit_HTU21DF ABC;
Adafruit_Si7021 sensor = Adafruit_Si7021();
void setup() {
Serial.begin(115200);
I2Csensor.begin(I2C_SDA, I2C_SCL, 100000);
//
// Could you provide an example of required code
//
// wait for serial port to open
while (!Serial) {
delay(10);
}
Serial.println(“Si7021 test!”);

if (!sensor.begin()) {
Serial.println(“Did not find Si7021 sensor!”);
while (true)
;
}
Serial.print(“Found model “);
switch(sensor.getModel()) {
case SI_Engineering_Samples:
Serial.print(“SI engineering samples”); break;
case SI_7013:
Serial.print(“Si7013”); break;
case SI_7020:
Serial.print(“Si7020”); break;
case SI_7021:
Serial.print(“Si7021”); break;
case SI_UNKNOWN:
default:
Serial.print(“Unknown”);
}
Serial.print(” Rev(“);
Serial.print(sensor.getRevision());
Serial.print(“)”);
Serial.print(” Serial #”); Serial.print(sensor.sernum_a, HEX); Serial.println(sensor.sernum_b, HEX);
}
void loop() {
Serial.print(“Humidity: “);
Serial.print(sensor.readHumidity(), 2);
Serial.print(“\tTemperature: “);
Serial.println(sensor.readTemperature(), 2);
delay(1000);
// Toggle heater enabled state every 30 seconds
// An ~1.8 degC temperature increase can be noted when heater is enabled
if (++loopCnt == 30) {
enableHeater = !enableHeater;
sensor.heater(enableHeater);
Serial.print(“Heater Enabled State: “);
if (sensor.isHeaterEnabled())
Serial.println(“ENABLED”);
else
Serial.println(“DISABLED”);

loopCnt = 0;
}
}

It also would be most appreciated, If you could provide or direct me to information regarding interpreting the outcome needs from the library file statements we have been discussing. This is so if I have a need to use a different sensor in the future and it’s not one you have provided the way forward for, I can interpret the instruction by myself.

Best Regard
Dave

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David Fenner answered 4 days ago

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Sara Santos Staff answered 2 days ago

Hi.
As I mentioned you need to take a look at the library files and see which arguments each function requires.

In this case, it accepts the TwoWire instance when creating the Adafruit_Si7021 instance.

So, you need to pass the TwoWire instance like this:

TwoWire I2Csensor = TwoWire(0);
//Adafruit_HTU21DF ABC;
Adafruit_Si7021 sensor = Adafruit_Si7021(I2Csensor);

The rest of the code should remain the same.

I hope this helps.

Regards,
Sara

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David Fenner answered 19 hours ago

Hi Sara,
Thank you for your reply, I have updated my sketch as per your suggestion (see below) unfortunately I get the following error.
Could you further help me.
C:\Users\Me\Documents\Arduino\ESP32_C6_2025_SI7021_Example_Temp\ESP32_C6_2025_SI7021_Example_Temp.ino:11:51: error: no matching function for call to ‘Adafruit_Si7021::Adafruit_Si7021(TwoWire&)’ 11 | Adafruit_Si7021 sensor = Adafruit_Si7021(I2Csensor); | ^ In file included from C:\Users\Me\Documents\Arduino\ESP32_C6_2025_SI7021_Example_Temp\ESP32_C6_2025_SI7021_Example_Temp.ino:1: C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:81:3: note: candidate: ‘Adafruit_Si7021::Adafruit_Si7021(TwoWire*)’ 81 | Adafruit_Si7021(TwoWire *theWire = &Wire); | ^~~~~~~~~~~~~~~ C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:81:28: note: no known conversion for argument 1 from ‘TwoWire’ to ‘TwoWire*’ 81 | Adafruit_Si7021(TwoWire *theWire = &Wire); | ~~~~~~~~~^~~~~~~~~~~~~~~ C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:79:7: note: candidate: ‘constexpr Adafruit_Si7021::Adafruit_Si7021(const Adafruit_Si7021&)’ 79 | class Adafruit_Si7021 { | ^~~~~~~~~~~~~~~ C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:79:7: note: no known conversion for argument 1 from ‘TwoWire’ to ‘const Adafruit_Si7021&’ C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:79:7: note: candidate: ‘constexpr Adafruit_Si7021::Adafruit_Si7021(Adafruit_Si7021&&)’ C:\Users\Me\Documents\Arduino\libraries\Adafruit_Si7021_Library/Adafruit_Si7021.h:79:7: note: no known conversion for argument 1 from ‘TwoWire’ to ‘Adafruit_Si7021&&’ exit status 1 Compilation error: no matching function for call to ‘Adafruit_Si7021::Adafruit_Si7021(TwoWire&)’

My sketch:

#include “Adafruit_Si7021.h”
bool enableHeater = false;
uint8_t loopCnt = 0;
#define I2C_SDA 1
#define I2C_SCL 2
TwoWire I2Csensor = TwoWire(0);
Adafruit_Si7021 sensor = Adafruit_Si7021(I2Csensor);
void setup() {
Serial.begin(115200);
I2Csensor.begin(I2C_SDA, I2C_SCL, 100000);
// wait for serial port to open
while (!Serial) {
delay(10);
}
Serial.println(“Si7021 test!”);

if (!sensor.begin()) {
Serial.println(“Did not find Si7021 sensor!”);
while (true)
;
}
Serial.print(“Found model “);
switch(sensor.getModel()) {
case SI_Engineering_Samples:
Serial.print(“SI engineering samples”); break;
case SI_7013:
Serial.print(“Si7013”); break;
case SI_7020:
Serial.print(“Si7020”); break;
case SI_7021:
Serial.print(“Si7021”); break;
case SI_UNKNOWN:
default:
Serial.print(“Unknown”);
}
Serial.print(” Rev(“);
Serial.print(sensor.getRevision());
Serial.print(“)”);
Serial.print(” Serial #”); Serial.print(sensor.sernum_a, HEX); Serial.println(sensor.sernum_b, HEX);
}
void loop() {
Serial.print(“Humidity: “);
Serial.print(sensor.readHumidity(), 2);
Serial.print(“\tTemperature: “);
Serial.println(sensor.readTemperature(), 2);
delay(1000);
// Toggle heater enabled state every 30 seconds
// An ~1.8 degC temperature increase can be noted when heater is enabled
if (++loopCnt == 30) {
enableHeater = !enableHeater;
sensor.heater(enableHeater);
Serial.print(“Heater Enabled State: “);
if (sensor.isHeaterEnabled())
Serial.println(“ENABLED”);
else
Serial.println(“DISABLED”);

loopCnt = 0;
}
}

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Sara Santos Staff answered 5 hours ago

Hi,

Change this line

Adafruit_Si7021 sensor = Adafruit_Si7021(I2Csensor);

Adafruit_Si7021 sensor = Adafruit_Si7021(&I2Csensor)

Let me know if this fixes the issue.

Regards,
Sara