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113 lines
5.1 KiB
113 lines
5.1 KiB
void dtu21()
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{ //Set the address of the HTU21D. This detail is hidden at the bototm of page 10 of the datasheet.
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const int I2C_address = 0x40; // I2C write address. Note that 'const' has been declared. If you try to write to this variable
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// anywhere else in your code you'll get a compilation error. This prevents you from doing silly things.
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const int TempCode = 0xE3; // A temperature measurement is executed with this command code. See page 11 of datasheet.
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const int HumidCode = 0xE5; // A humidity measurement is executed with this command code. See page 11 of datasheet.
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long Temperature; //Perform our calculation using LONG to prevent overflow at high measuremetn values when using 14bit mode.
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long Humidity;
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float TemperatureFL; //Variable to store our final calculated temperature measurement
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float HumidityFL;
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delay(100); // a short delay to let everything stabilise
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delay(10); //add a small delay to slow things down
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RequestMeas(I2C_address, TempCode); //Request the current temperature
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Temperature = ReadMeas(I2C_address); //read the result
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//We must now convert our temp measurement into an actual proper temperature value
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//According to page 15, the conversion equation is: Temp = -46.85 + 175.72 x TeampMeas / 2^16
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//Becasue the result will have decimal places in the result we must use a Float datatype.
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// TemperatureFL = (Temperature/65536.0)*175.72-46.85 ;
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TemperatureFL = (Temperature/65536.0)*175.72-46.85-1.1 ;
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delay(100); //add a small delay to slow things down
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RequestMeas(I2C_address, HumidCode); //Request the current humidity
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Humidity = ReadMeas(I2C_address); //read the result
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//We must now convert our humidity measurement into an actual proper humidity value
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//According to page 15, the conversion equation is: Humidity = 6 + 125 x TeampMeas / 2^16
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//Becasue the result will have decimal places in the result we must use a Float datatype.
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//HumidityFL = -6 + 125*(Humidity/pow(2, 16));
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HumidityFL =(Humidity/65536.0)*125.0-6.0;
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tc=TemperatureFL;
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td=abs(TemperatureFL*10-tc*10);
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hc=HumidityFL;
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hd=HumidityFL*10-hc*10;
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if (tc<0){zn=0;}
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//All the calculations are complete, lets now display our values for temperature and humidity on the serial port.
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// Serial.print("Temperature:");
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// Serial.print(TemperatureFL);
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// Serial.print("\t");
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// Serial.print(tc);
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// Serial.print(".");
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// Serial.print(td);
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// Serial.print("\t");
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// Serial.print("Humidity:");
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//Serial.print(HumidityFL);
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// Serial.print("\t");
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// Serial.print(hc);
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// Serial.print(".");
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// Serial.println(hd);
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}
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void RequestMeas(int Address, int CommandCode)
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{
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Wire.beginTransmission(Address); // The HTU21D will respond to its address
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Wire.write(CommandCode); // request the measurement, ie temperature or humidity
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Wire.endTransmission();
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return;
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}
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long ReadMeas(int Address)
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{
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//A measurement from the HTU21D is returned in 3 consecutive bytes. See page 11 of the datasheet
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//the order of returend data is: [DATA (Most Sig Byte)], [DATA (Least Sig Byte)], [Checksum]
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//We will ignore the checksum to save computation time and complexity. Page 14 of the datasheet details how to calculate the checksum
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byte DataHIGH; //The location to store the high measurement byte
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byte DataLOW; //The low measurement byte
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byte CRC; //If you want to compute the CRC feel free to do so.
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long Data; //The temporary memory location we are storing our data in as we receive it from the HTU21D
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//Each packet of data is only 8bits in length, but if we do a bit shift we can store the 2 packets of
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//measurement data in a variable. Remember you can only return 1 variable when a function finishes.
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//Ideally, we'd use an int to store the result, however, at high measurement values in 14bit mode, an int overflows.
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//To prevent overflow, we must use a single long (32bits).
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Wire.requestFrom(Address, 3); //We are requesting data from the HTU21D and there will be 3x bytes that must be read.
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while(Wire.available()) // Check for data from the HTU21D
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{
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DataHIGH = Wire.read(); // Read high byte
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DataLOW = Wire.read(); // Read low byte
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CRC = Wire.read(); // Read the CRC byte
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}
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//OK, so now we are going to 'pack' our 2x bytes of data measuremetns into a single int so only 1 variable is returned.
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//To do this, we will use the left bitshift operator '&lt;&lt;'. What this does is push all the bits across to the left.
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//FUN FACT: performing a left bit shift is equivalent to multiplication by 2 for each shift. The reverse is true for right
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//bitshift which is equivalent to dividing by 2. This is a far more efficient method to perform multiply or divide by 2.
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Data = DataHIGH; //The data sits in the low byte of 'int Data'.
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//Ie, Data = [00000000][00000000][00000000][8 bits of DataHIGH]
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//data[1] &lt;&lt; 8
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//Data = Data &lt;&lt; 8; //Shift all the bits to the left for 8 bits. The old locations fill with zeros.
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Data = Data<<8;
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//Ie, Data = [00000000][00000000][8 bits of DataHIGH][00000000]
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Data = Data + DataLOW; //Now simply add the low byte of data to the int.
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//Ie, Data = [00000000][00000000][8 bits of DataHIGH][8 bits of DataLOW]
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return Data; //return our measurement.
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}
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