ESP8266 Community Forum

- Sun Apr 17, 2016 12:40 pm #45644 I have a few SI7021 sensors that I want to read with a ESP-21. I'm pretty sure I've had it working a few months ago, but forgot what library I used for it

The sensors are i2c sensors, and when I use a i2c scanner, I can find them on address 0x40. The problem is that whatever library I use, I seem to get bogus values out of it. For instance, when I use the example here: http://www.instructables.com/id/MINI-Si ... LSTEPSTemp RH

I get values like:

Temp RH
-47.54C -6.49%

When I pull out the sensor, I get the same kind of values, so it seems like the code is not even doeing anything with the sensor. I tried a few sensors (to make sure I didn't have a broken one), but the result was the same.

The libraries on https://github.com/LowPowerLab/SI7021 and https://github.com/mlsorensen/SI7021 also don't give the right results.

Any ideas?

- Mon Apr 18, 2016 12:15 pm #45733 Did some more testing, hooked up the same sensor to a arduino nano, and loaded in the sketch down below.
Worked like a charm... So I'm a bit clueless why it's not working on the ESP. I've used other i2c sensor before without problems.

My connections are like this by the way:

GPIO05 --> SCL
GPIO04 --> SDA
3.3v --> VIN
GND --> GND

Code: Select all#include <Wire.h>
#include <Si7021.h>

SI7021 si7021;

// BASIC DEMO
// ----------
// Print humidity and temperature to the serial monitor while toggling the heater on and off
// periodically.

// NOTE ON RESOLUTION:
// -------------------
// Changing the resolution of the temperature will also change the humidity resolution.
// Likewise, changing the resolution of the humidity will also change temperature resolution.
// Two functions are provided to change the resolution, both functions are similar except they have
// different masks to the registers, so setTempRes(14) will change the temp resolution to 14-bit
// but humidity will also be set to 12-bit. Setting the humidity resolution to 8-bit setHumidityRes(8)
// will change the temperature resolution to 12-bit.
// Resolution Table:
//                    14-bit Temp <-> 12-bit Humidity
//                    13-bit Temp <-> 10-bit Humidity
//                    12-bit Temp <->  8-bit Humidity
//                    11-bit Temp <-> 11-bit Humidity

// NOTE ON HEATER:
// ---------------
// The HTRE bit in the user register is what turns the heater on and off. This register
// is stored on non-volatile memory to it will keep its state when power is removed. If
// the heater is enabled and power is removed before the program had chance to turn it off
// then the heater will remain enabled the next time it is powered on. The heater has to
// be explicitly turned off. In the begin() function for this library, a reset procedure
// will take place and reset the user register to default, so the heater will be turned off
// and the resolution will also be set to default, 14-bit temperature and 12-bit humidity.
// Keep this in mind if testing and swapping sensors/libraries.

void setup()
{
Serial.begin(115200);
si7021.begin(); // Runs : Wire.begin() + reset()
  while(!Serial); // Wait for serial monitor to open
Serial.println("BASIC DEMO");
Serial.println("------------------------------------------");
si7021.setHumidityRes(12); // Humidity = 12-bit / Temperature = 14-bit
}

void loop()
{
static uint8_t heaterOnOff; // Create static variable for heater control
si7021.setHeater(heaterOnOff); // Turn heater on or off
Serial.print("Heater Status = ");
Serial.println(si7021.getHeater() ? "ON" : "OFF");

  for(int i = (heaterOnOff ? 20 : 30); i>0; i--)
  {
  Serial.print("Humidity : ");
  Serial.print(si7021.readHumidity()); // Read humidity and print to serial monitor
  Serial.print(" %\t");
  Serial.print("Temp : ");
  Serial.print(si7021.readTemp()); // Read temperature and print to serial monitor
  Serial.print(" C\t");
  Serial.println(i); // Print count down for heater change
  delay(500);
  }

heaterOnOff = !heaterOnOff; // Toggle heater on/off variable
}


- Mon Apr 18, 2016 12:35 pm #45735 Take a look at your I2C pull-up resitors. Might be from there. How many devices do you have on your I2C Bus? You need the resistors only once on the bus.

For a quick test and a deeper look, this SI7021 related Article might help you.

ESP8266 MPDMv4 AC MAINS Dimmer Home: http://esp8266-projects.com/2016/04/mpdmv4-mains-dimmerswitch-html/
Available on Tindie: https://www.tindie.com/products/nEXT_EVO1/universal-ac-mains-dimmer-mpdmv41/

- Mon Apr 18, 2016 1:50 pm #45738 Thanks for the info. I already had the pullup resistors in place. Added a capacitator now, but no success yet. I'll have a look at the article, seems to have a lot of interesting background info too.