ESP8266 Community Forum

Hello friends,

I tryed to work with si7021 + esp12 and Arduino IDE.
I spent half a day but no any success, i tryed few libs incl sparkfun hu21 and nothing, just isnt real values.

I work with esp&arduino ide with bmp180,dht11,lux sensor and etc, but i cant reach success with si7021.

Does anyone reach it, if yes, how? May be need specific lib. Thx

Hi KoliaS

It look this is a matter of timing between Si7021 and ESP8266 communication... i'm not an expert in I2C stuff..
I had the same problem using Si7021 arduino library in the file Si7021.cpp ... spent hours tweaking various things... and finally found solution on the web but on a different library, but principal is the same: add delay time right after request is sent to Si7021. Please check " delay(85);" here below.
I have just tried the 85 and it worked at first run, but you may have to tweak this delay.

Hope this helps.

#include "Si7021.h"
#include <Wire.h>

#define RH_CALC(n) (((125 * (float) (n)) / 65536) - 6)
#define TEMP_CALC(n) (((175.72f * (n)) / 65536) - 46.85f)

#define SI7021_ADDR 0x40

SI7021::SI7021()
{
}

void SI7021::begin()
{
Wire.begin(); // Begin I2C
reset(); // Reset sensor

}

float SI7021::readHumidity()
{
return RH_CALC(readSensor(0xE5)); // Return humidity
}

float SI7021::readTemp()
{
return TEMP_CALC(readSensor(0xE3)); // Return temp

}

float SI7021::readTempPrev()
{
return TEMP_CALC(readSensor(0xE0)); // Return previous temp
}

void SI7021::setHumidityRes(uint8_t res)
{
uint8_t uReg = readRegister(0xE7); // Read user register
if(res == 12) uReg &= ~(0x81); // Set 12-bit humidity
if(res == 11) uReg |= (0x81); // Set 11-bit humidity
if(res == 10) uReg = (uReg & ~(0x81)) | (0x80); // Set 10-bit humidity
if(res == 8) uReg = (uReg & ~(0x81)) | (0x01); // Set 8-bit humidity
writeRegister(0xE6, uReg); // Write user register
}

void SI7021::setTempRes(uint8_t res)
{
uint8_t uReg = readRegister(0xE7); // Read user register
if(res == 14) uReg &= ~(0x81); // Set 14-bit temp
if(res == 13) uReg = (uReg & ~(0x80)) | (0x80); // Set 13-bit temp
if(res == 12) uReg = (uReg & ~(0x80)) | (0x01); // Set 12-bit temp
if(res == 11) uReg |= (0x81); // Set 11-bit temp
writeRegister(0xE6, uReg); // Write user register
}

uint8_t SI7021::getHumidityRes()
{
uint8_t resBits = readRegister(0xE7) & (0x81); // Read resolution bits
if(resBits == 0x00) return 12; // Return humidity 12-bit
if(resBits == 0x81) return 11; // Return humidity 11-bit
if(resBits == 0x80) return 10; // Return humidity 10-bit
if(resBits == 0x01) return 8; // Return humidity 8-bit
return 0; // Return 0 for error
}

uint8_t SI7021::getTempRes()
{
uint8_t resBits = readRegister(0xE7) & (0x81); // Read resolution bits
if(resBits == 0x00) return 14; // Return temp 14-bit
if(resBits == 0x80) return 13; // Return temp 13-bit
if(resBits == 0x01) return 12; // Return temp 12-bit
if(resBits == 0x81) return 11; // Return temp 11-bit
return 0; // Return 0 for error
}

void SI7021::setHeater(uint8_t hBit)
{
uint8_t uReg = readRegister(0xE7); // Read user register
if(hBit) uReg |= (0x04); // Set heater bit - ON
else uReg &= ~(0x04); // Set heater bit - OFF
writeRegister(0xE6, uReg); // Write user register
}

uint8_t SI7021::getHeater()
{
return ((readRegister(0xE7) & (0x04)) ? 1 : 0); // Return heater status
}

/*
void SI7021::setHeaterPower(uint8_t hPow)
{
uint8_t hReg = readRegister(0x11); // Read heater register
if(hPow == 1) hReg &= ~(0x0F); // Set current 3.09mA
if(hPow == 2) hReg = (hReg & ~(0x0F)) | (0x01); // Set current 9.18mA
if(hPow == 3) hReg = (hReg & ~(0x0F)) | (0x02); // Set current 15.24mA
if(hPow == 4) hReg = (hReg & ~(0x0F)) | (0x04); // Set current 27.39mA
if(hPow == 5) hReg = (hReg & ~(0x0F)) | (0x08); // Set current 51.69mA
if(hPow == 6) hReg |= (0x0F); // Set current 94.20mA
writeRegister(0x51, hReg); // Write heater register
}

uint8_t SI7021::getHeaterPower()
{
uint8_t hReg = readRegister(0x11); // Read heater register
if(hReg == 0x00) return 3; // Return current 3mA
if(hReg == 0x01) return 9; // Return current 9mA
if(hReg == 0x02) return 15; // Return current 15mA
if(hReg == 0x04) return 27; // Return current 27mA
if(hReg == 0x08) return 51; // Return current 51mA
if(hReg == 0x0F) return 94; // Return current 94mA
return 0; // Return 0 for error
}
*/

uint16_t SI7021::getDeviceID()
{
Wire.beginTransmission(SI7021_ADDR);
Wire.write(0xFC); // Send first address byte
Wire.write(0xC9); // Send second address byte
Wire.endTransmission(false);
delay(85);
Wire.requestFrom(SI7021_ADDR, 1); // Request first byte
uint8_t SNB3 = Wire.read(); // Read SNB3 byte (ID)
if(SNB3 == 0x0D) return 7013; // Device is Si7013
else if(SNB3 == 0x14) return 7020; // Device is Si7020
else if(SNB3 == 0x15) return 7021; // Device is Si7021
else if(SNB3 == 0x00) return 255; // Engineering sample
else if(SNB3 == 0xFF) return 255; // Engineering sample
else return 0; // Device unknown

}

uint8_t SI7021::getFirmwareVer()
{
Wire.beginTransmission(SI7021_ADDR);
Wire.write(0x84); // Send first address byte
Wire.write(0xB8); // Send second address byte
Wire.endTransmission(false);
delay(85);
Wire.requestFrom(SI7021_ADDR, 1); // Request first byte
uint8_t fwV = Wire.read(); // Read firmware version
if(fwV == 0x20) return 2; // Firmware version 2.0
else if(fwV == 0xFF) return 1; // Firmware version 1.0
else return 0; // Firmware version unknown
}

uint8_t SI7021::checkVDD()
{
return (readRegister(0xE7) & (0x40)) ? 0 : 1; // Return 0=LOW / 1=OK
}

void SI7021::reset(uint8_t delayR)
{
Wire.beginTransmission(SI7021_ADDR);
Wire.write(0xFE); // Write reset command
Wire.endTransmission();
delay(delayR); // Default = 15ms
}

uint16_t SI7021::floatToInt(float FtoI)
{
return FtoI*100; // Converts float to int
} // keeping full precision

float SI7021::intToFloat(uint16_t ItoF)
{
return (float)ItoF/100; // Convert int to float
} // keeping full precision

float SI7021::CtoF(float tempC)
{
return tempC * 9 / 5 + 32; // Returns temp in F
}

float SI7021::FtoC(float tempF)
{
return (tempF - 32) * 5 / 9; // Returns temp in C
}

/* PRIVATE: PRIVATE: PRIVATE: PRIVATE: PRIVATE: PRIVATE: PRIVATE: PRIVATE: */

void SI7021::writeRegister(uint8_t reg, uint8_t value)
{
Wire.beginTransmission(SI7021_ADDR);
Wire.write(reg);
Wire.write(value);
Wire.endTransmission();
}

uint8_t SI7021::readRegister(uint8_t reg)
{
Wire.beginTransmission(SI7021_ADDR);
Wire.write(reg);
Wire.endTransmission(false);
delay(85);
Wire.requestFrom(SI7021_ADDR, 1);
return Wire.read();
}

uint16_t SI7021::readSensor(uint8_t reg)
{
uint16_t var = 0;
Wire.beginTransmission(SI7021_ADDR);
Wire.write(reg);
Wire.endTransmission(false);
delay(85);
Wire.requestFrom(SI7021_ADDR, 2);
var = Wire.read() << 8;
var |= Wire.read() & 0x0FF;
return var;
}