Question

I am using a soft I²C implementation to read a set of Sensirion SHT21 sensors. I am trying to figure out a way of having the sensors answer to see if they are actually connected to the device. I am using the Arduino which means all my code is C/C++

The libraries I am using are here.

The code used to read the sensors is the following:

#include <Ports.h>
#include <PortsSHT21.h>

//Define soft I²C channels for three sensors
SHT21 hsensor2 (2); // pins A1 and D5 - Sensor 2

//define variables for temp data
float h, t;

void setup() {}

void loop()
{
    // Get data from sensor soft I²C
    hsensor2.measure(SHT21::HUMI);
    hsensor2.measure(SHT21::TEMP);
    hsensor2.calculate(h, t);
    float hum2 = (h);
    float temp2 = (t);
}

Answer 1

The large code block is the code for the measure() function. Notice that it returns 0 at one point without performing a connReset(). This should be a way to detect a valid device such as …

bool hasHUMI;
if (hsensor2.measure(SHT21::HUMI))
{
  hasHUMI=true;
}

or

if (hsensor2.measure(SHT21::HUMI) && hsensor2.measure(SHT21::TEMP))
{
 hsensor2.calculate(h, t); 
 float hum2 = (h); 
 float temp2 = (t);    
}

or

Your code should be clearing h and t to 0 before making the read so that you can test for valid values. Like this…

void loop() 
{ 
    h=0.00f;
    t=0.00f;
    // Get data from sensor soft I²C 
    hsensor2.measure(SHT21::HUMI); 
    hsensor2.measure(SHT21::TEMP); 
    hsensor2.calculate(h, t); 
    float hum2 = (h); 
    float temp2 = (t); 
    if (h>0) {
    }
    if (t>0) {
    }
} 

If not then you could make (copy) your own version of the measure() function that tests for valid return value in meas[type]. You would need to set meas[type] to a known invalid value before the read (such as 0).

uint8_t SHT21::measure(uint8_t type, void (*delayFun)()) {

    start();
    writeByte(type == TEMP? MEASURE_TEMP : MEASURE_HUMI)

    for (uint8_t i = 0; i < 250; ++i) {
        if (!digiRead()) {
            meas[type] = readByte(1) << 8;
            meas[type] |= readByte(1);
            uint8_t flipped = 0;

            for (uint8_t j = 0x80; j != 0; j >>= 1) {
                flipped >>= 1;
            }

            if (readByte(0) != flipped)
                break;

            return 0;
        }


        if (delayFun)
            delayFun();
        else
            delay(1);
    }

    connReset();
    return 1;
}

You probably know that if you add a method to a library cpp then you also need to add a corresponding prototype to the .h otherwise the arduino will fail to compile your code.

.cpp

uint8_t SHT21::measureTest(uint8_t type, void (*delayFun)()) {

    }

.h

uint8_t measureTest(uint8_t type, void (*delayFun)() =0);