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How to check if SHT15 is connected or not to i2c

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hssn601

Joined: 31 Jan 2014
Posts: 20

How to check if SHT15 is connected or not to i2c

Posted: Mon Apr 14, 2014 12:23 am

I am using the following driver for reading temperature and humidity.

Code:

///////////////////////////////////////////////////////////////////////////////
// //
// Driver file for SHT15 Temperature & Humidity Sensor //
// //
// ***** To initialise SHT15 sensor upon power up ***** //
// //
// Function : sht_init() //
// Return : none //
// //
// //
// ***** To measure and calculate SHT15 temp & real RH ***** //
// //
// Function : sht_rd (temp, truehumid) //
// Return : temperature & true humidity in float values //
// //
///////////////////////////////////////////////////////////////////////////////

#define sht_data_pin PIN_B5
#define sht_clk_pin PIN_B6

//***** Function to alert SHT15 *****

void comstart (void)
{
output_float(sht_data_pin); //data high OUT
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_bit(sht_data_pin, 0); //data low
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
delay_us(2);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_float(sht_data_pin); //data high
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
}

//***** Function to write data to SHT15 *****

int1 comwrite (int8 iobyte)
{
int8 i, mask = 0x80;
int1 ack;

//Shift out command
delay_us(4);
for(i=0; i<8; i++)
{
output_bit(sht_clk_pin, 0); //clk low
if((iobyte & mask) > 0) output_float(sht_data_pin); //data high if MSB high
else output_bit(sht_data_pin, 0); //data low if MSB low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
mask = mask >> 1; //shift to next bit
}

//Shift in ack
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
ack = input(sht_data_pin); //get ack bit
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
return(ack);
}

//***** Function to read data from SHT15 *****

int16 comread (void)
{
int8 i;
int16 iobyte = 0;
const int16 mask0 = 0x0000;
const int16 mask1 = 0x0001;

//shift in MSB data
for(i=0; i<8; i++)
{
iobyte = iobyte << 1;
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
else iobyte |= mask0;
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
}

//send ack 0 bit
output_bit(sht_data_pin, 0); //data low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(2);
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
output_float(sht_data_pin); //data high

//shift in LSB data
for(i=0; i<8; i++)
{
iobyte = iobyte << 1;
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
else iobyte |= mask0;
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
}

//send ack 1 bit
output_float(sht_data_pin); //data high
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(2);
output_bit(sht_clk_pin, 0); //clk low

return(iobyte);
}

//***** Function to wait for SHT15 reading *****

void comwait (void)
{
int16 sht_delay;

output_float(sht_data_pin); //data high
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
for(sht_delay=0; sht_delay<30000; sht_delay++) // wait for max 300ms
{
if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT15 ready
delay_us(10);
}
}

//***** Function to reset SHT15 communication *****

void comreset (void)
{
int8 i;

output_float(sht_data_pin); //data high
output_bit(sht_clk_pin, 0); //clk low
delay_us(2);
for(i=0; i<9; i++)
{
output_bit(sht_clk_pin, 1); //toggle clk 9 times
delay_us(2);
output_bit(sht_clk_pin, 0);
delay_us(2);
}
comstart();
}

//***** Function to soft reset SHT15 *****

void sht_soft_reset (void)
{
comreset(); //SHT15 communication reset
comwrite(0x1e); //send SHT15 reset command
delay_ms(15); //pause 15 ms
}

//***** Function to measure SHT15 temperature *****

int16 measuretemp (void)
{
int1 ack;
int16 iobyte;

comstart(); //alert SHT15
ack = comwrite(0x03); //send measure temp command and read ack status
if(ack == 1) return;
comwait(); //wait for SHT15 measurement to complete
iobyte = comread(); //read SHT15 temp data
return(iobyte);
}

//***** Function to measure SHT15 RH *****

int16 measurehumid (void)
{
int1 ack;
int16 iobyte;

comstart(); //alert SHT15
ack = comwrite(0x05); //send measure RH command and read ack status
if(ack == 1) return;
comwait(); //wait for SHT15 measurement to complete
iobyte = comread(); //read SHT15 temp data
return(iobyte);
}

//***** Function to calculate SHT15 temp & RH *****

void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue)
{
float rh;

//calculate temperature reading
tc = ((float) temp * 0.01) - 39.6;

//calculate Real RH reading
rh = (float) humid;

rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0;

//calculate True RH reading
rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin;
}

//***** Function to measure & calculate SHT15 temp & RH *****

void sht_rd (float & temp, float & truehumid)
{
int16 restemp, reshumid;
float realhumid;
restemp = 0; truehumid = 0;

restemp = measuretemp(); //measure temp
reshumid = measurehumid(); //measure RH
calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH
}

//***** Function to initialise SHT15 on power-up *****

void sht_init (void)
{
comreset(); //reset SHT15
delay_ms(20); //delay for power-up
}

The problem is that if i plugged out the sensor than it shows:
Humidity=-4.6
Temperature=-39.5

I want to know how to detect weather sensor is connected or not.

Ttelmah

Joined: 11 Mar 2010
Posts: 19346


Posted: Mon Apr 14, 2014 12:45 am

Look at the I2C bus scanner program in the code library. This scans the I2C bus, looking for acknowledgements from devices. You can do exactly the same for the single address of your device. If it acknowledges, then it is present. If not, then you know not to call the driver. Best Wishes

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