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J
JMerc
Visitor II
September 4, 2019
Question

HTS221 Temperature sensor

  • September 4, 2019
  • 2 replies
  • 1783 views

Hello,

I have one Arduino MKR ENV board which has this sensor. The problem is that I'm reading higher temperature values than expected.

The routines that I use are :

For calibration:

 /**
 
 * HTS221_readCalibration
 
 *
 
 * Reads calibration values
 
 * @return char - != 0 if any error happened
 
 */
 
char HTS221::readCalibration(void) {
 
	unsigned char T0_degC_x8_H;
 
	unsigned char T0_degC_x8_L;
 
	unsigned char T1_degC_x8_H;
 
	unsigned char T1_degC_x8_L;
 
	
 
	unsigned char H0_rh_x2;
 
	unsigned char H1_rh_x2;
 
	
 
	int temp;
 
 
 
	DEBUG("HTS221 - Reading Calibration: ");
 
	DEBUG("\n\r");
 
	
 
	/**
 
 * Humidity calibration values
 
 */
 
	if((temp = readReg(HTS221_H0_RH_X2)) < 0) return 1;
 
	H0_rh_x2 = (unsigned char)temp;
 
	H0_rh = H0_rh_x2 / 2.0;
 
	
 
	DEBUG("HTS221 - H0_rh: ");
 
	DEBUGF(H0_rh, 2);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_H1_RH_X2)) < 0) return 2;
 
	H1_rh_x2 = (unsigned char)temp;
 
	H1_rh = H1_rh_x2 / 2.0;
 
	
 
	DEBUG("HTS221 - H1_rh: ");
 
	DEBUGF(H1_rh, 2);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_H0_T0_OUT_L)) < 0) return 3;
 
	H0_T0_out = (unsigned char)temp;
 
	if((temp = readReg(HTS221_H0_T0_OUT_H)) < 0) return 4;
 
	H0_T0_out |= ((unsigned char)temp << 8);
 
	
 
	DEBUG("HTS221 - H0_T0_out: ");
 
	DEBUGF(H0_T0_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_H1_T0_OUT_L)) < 0) return 5;
 
	H1_T0_out = (unsigned char)temp;
 
	if((temp = readReg(HTS221_H1_T0_OUT_H)) < 0) return 6;
 
	H1_T0_out |= ((unsigned char)temp << 8);
 
	
 
	DEBUG("HTS221 - H1_T0_out: ");
 
	DEBUGF(H1_T0_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	
 
	/**
 
 * Temperature calibration values
 
 */
 
	if((temp = readReg(HTS221_T1T0_MSB)) < 0) return 7;
 
	DEBUG("HTS221_T1T0_MSB - 0x35: 0x");
 
	DEBUGF(temp, HEX); DEBUG(" decimal="); DEBUGF(temp, DEC);
 
	DEBUG("\n\r");
 
	T0_degC_x8_H = (unsigned char)(temp & 0x03);
 
	
 
	
 
	if((temp = readReg(HTS221_T0_DEGC_X8)) < 0) return 8;
 
	T0_degC_x8_L = (unsigned char)temp;
 
	DEBUG("HTS221_T0_DEGC_X8 - 0x32: 0x");
 
	DEBUGF(T0_degC_x8_L, HEX); DEBUG(" decimal="); DEBUGF(T0_degC_x8_L, DEC);
 
	DEBUG("\n\r");
 
	
 
	
 
	T0_degC = (((T0_degC_x8_H << 8) | T0_degC_x8_L)) / 8.0;
 
	DEBUG("HTS221 - T0_degC: ");
 
	DEBUGF(T0_degC, 2);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_T1T0_MSB)) < 0) return 9;
 
	T1_degC_x8_H = (unsigned char)((temp & 0x0C) >> 2);
 
	
 
	if((temp = readReg(HTS221_T1_DEGC_X8)) < 0) return 10;
 
	T1_degC_x8_L = (unsigned char)temp;
 
	DEBUG("HTS221_T1_DEGC_X8 - 0x33: 0x");
 
	DEBUGF(T1_degC_x8_L, HEX); DEBUG(" decimal="); DEBUGF(T1_degC_x8_L, DEC);
 
	DEBUG("\n\r");
 
	
 
	T1_degC = ((T1_degC_x8_H << 8) | T1_degC_x8_L) / 8.0;
 
	DEBUG("HTS221 - T1_degC: ");
 
	DEBUGF(T1_degC, 2);
 
	DEBUG("\n\r");
 
	
 
	
 
	if((temp = readReg(HTS221_T0_OUT_L)) < 0) return 11;
 
	T0_out = (unsigned char)temp;
 
	DEBUG("HTS221_T0_OUT_L - 0x3C: 0x");
 
	DEBUGF(T0_out, HEX); DEBUG(" decimal="); DEBUGF(T0_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_T0_OUT_H)) < 0) return 12;
 
	DEBUG("HTS221_T0_OUT_H - 0x3D: 0x");
 
	DEBUGF(temp, HEX); DEBUG(" decimal="); DEBUGF(temp, DEC);
 
	DEBUG("\n\r");
 
	
 
	T0_out |= ((unsigned char)temp << 8);
 
	DEBUG("HTS221 - T0_out: ");
 
	DEBUGF(T0_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_T1_OUT_L)) < 0) return 13;
 
	T1_out = (unsigned char)temp;
 
	DEBUG("HTS221_T1_OUT_L - 0x3E: 0x");
 
	DEBUGF(T1_out, HEX); DEBUG(" decimal="); DEBUGF(T1_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	if((temp = readReg(HTS221_T1_OUT_H)) < 0) return 14;
 
	DEBUG("HTS221_T1_OUT_H - 0x3F: 0x");
 
	DEBUGF(temp, HEX); DEBUG(" decimal="); DEBUGF(temp, DEC);
 
	DEBUG("\n\r");
 
	
 
	T1_out |= ((unsigned char)temp << 8);
 
	DEBUG("HTS221 - T1_out: ");
 
	DEBUGF(T1_out, DEC);
 
	DEBUG("\n\r");
 
	
 
	return 0;
 
}

For reading the values

float HTS221::readTemperature(void) {
 
	unsigned char temp;
 
	int value;
 
	float result;
 
	
 
	value = readReg(HTS221_TEMP_OUT_H);
 
	temp = (unsigned char)readReg(HTS221_TEMP_OUT_L);
 
	value = (value << 8) | temp;
 
	
 
	DEBUG("HTS221 - T_OUT: ");
 
	DEBUGF(value, DEC);
 
	DEBUG("\n\r");
 
	
 
	result = (((float)value - T0_out)/(T1_out - T0_out)) * (T1_degC - T0_degC) + T0_degC;
 
	
 
	DEBUG("HTS221 - Temperature value readed: ");
 
	DEBUGF(result, 2);
 
	DEBUG("\n\r");
 
	
 
	return result;
 
}

The registers' values are:

HTS221_T1T0_MSB - 0x35: 0xC4 decimal=196

HTS221_T0_DEGC_X8 - 0x32: 0xA7 decimal=167

HTS221 - T0_degC: 20.87

HTS221_T1_DEGC_X8 - 0x33: 0x14 decimal=20

HTS221 - T1_degC: 34.50

HTS221_T0_OUT_L - 0x3C: 0x3 decimal=3

HTS221_T0_OUT_H - 0x3D: 0x0 decimal=0

HTS221 - T0_out: 3

HTS221_T1_OUT_L - 0x3E: 0xEB decimal=235

HTS221_T1_OUT_H - 0x3F: 0x2 decimal=2

HTS221 - T1_out: 747

HTS221 - T_OUT: 354

HTS221 - Temperature value readed: 27.30

Is it problem of a faulty device?

Thanks in advance

Jordi Mercader

    This topic has been closed for replies.

    2 replies

    E
    Eleon BORLINI
    ST Employee
    September 26, 2019

    Hi @JMerc​ , sorry for the late answer, but it could be a lot-related issue... Basically your issue is that you are reading a temperature value constantly over a certain value, or does the value oscillate between a correct t range and higher temperatures? Do you have the possibility to test another device? Regards

    J
    JMercAuthor
    Visitor II
    September 30, 2019

    Hi Eleon,

    Thanks for your answer.

    The reading is always around 3ºC to 5ºC above the real temperature.

    I have another MKR ENV board and the readings were similar.

    Can you check if the calibration parameters are faulty?

    Best regards

    Jordi Mercader

    E
    Eleon BORLINI
    ST Employee
    September 30, 2019

    ​Hi Jordi, please check this thread if can be of your help. No issues about humidity value? Can you share the regmap dup described at that link? Regards

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