Example Code for a TMP102 I2c Thermometer————Arduino

参考：https://playground.arduino.cc/Code/TMP102/

Example Code for a TMP102 I2c Thermometer

I've fairly extensively commented the code, hopefully it makes sense. 

 

Example code for talking to a TMP102 I2C thermometer, like those available from Sparkfun, for example. Rather heavily based on some code I found in the forums, some  samples, and a bit of personal investigation to make it all work.  

 

Based on my testing, the sensor overreads by around 5 degrees C at room temperature. Not too sure if it is a percentage or a constant error. I know some of the analogue sensors are prone to incorrect readings if the reference voltages are off, but as we're using a digital output, this shouldn't affect it.  Any ideas? Mention them here.

 

For those using the Sparkfun logic converters with I2C, here are the pin connections:

 

• Low voltage to the 3.3v pin of the Arduino
• High voltage to the 5.0v pin
• High voltage Channel 1 Txo to the SDA pin (analog 4)
• High voltage Channel 2 Txo to the SCL pin (analog 5)
• Low voltage Channel 1 Txi to the SDA pin of tmp102
• Low voltage Channel 2 Txi to the SCL pin of tmp102
• The RX pins of the logic converter are not used
• V+ of tmp102 connected to 3.3v
• ADD0 of tmp102 connected to ground
• ALT of tmp102 not connected
• All grounds connected together.

 

You can instead use resistors to voltage divide the signal lines, but I've not figured out how to do that yet. 

 

1. #include "Wire.h"
2. #define TMP102_I2C_ADDRESS 72 /* This is the I2C address for our chip.
3. This value is correct if you tie the ADD0 pin to ground. See the datasheet for some other values. */
4.  
5.  
6. void setup() {
7.   Wire.begin(); // start the I2C library
8.   Serial.begin(115200); //Start serial communication at 115200 baud
9. }
10.  
11.  
12. void getTemp102(){
13.   byte firstbyte, secondbyte; //these are the bytes we read from the TMP102 temperature registers
14.   int val; /* an int is capable of storing two bytes, this is where we "chuck" the two bytes together. */
15.   float convertedtemp; /* We then need to multiply our two bytes by a scaling factor, mentioned in the datasheet. */
16.   float correctedtemp;
17.   // The sensor overreads (?)
18.  
19.  
20.   /* Reset the register pointer (by default it is ready to read temperatures)
21. You can alter it to a writeable register and alter some of the configuration -
22. the sensor is capable of alerting you if the temperature is above or below a specified threshold. */
23.  
24.   Wire.beginTransmission(TMP102_I2C_ADDRESS); //Say hi to the sensor.
25.   Wire.send(0x00);
26.   Wire.endTransmission();
27.   Wire.requestFrom(TMP102_I2C_ADDRESS, 2);
28.   Wire.endTransmission();
29.  
30.  
31.   firstbyte      = (Wire.receive());
32. /*read the TMP102 datasheet - here we read one byte from
33.  each of the temperature registers on the TMP102*/
34.   secondbyte     = (Wire.receive());
35. /*The first byte contains the most significant bits, and
36.  the second the less significant */
37.     val = ((firstbyte) << 4);  
38.  /* MSB */
39.     val |= (secondbyte >> 4);    
40. /* LSB is ORed into the second 4 bits of our byte.
41. Bitwise maths is a bit funky, but there's a good tutorial on the playground*/
42.     convertedtemp = val*0.0625;
43.     correctedtemp = convertedtemp - 5;
44.     /* See the above note on overreading */
45.  
46.  
47.   Serial.print("firstbyte is ");
48.   Serial.print(" ");
49.   Serial.println(firstbyte, BIN);
50.   Serial.print("secondbyte is ");
51.   Serial.print(" ");
52.   Serial.println(secondbyte, BIN);
53.   Serial.print("Concatenated byte is ");
54.   Serial.print(" ");
55.   Serial.println(val, BIN);
56.   Serial.print("Converted temp is ");
57.   Serial.print(" ");
58.   Serial.println(val*0.0625);
59.   Serial.print("Corrected temp is ");
60.   Serial.print(" ");
61.   Serial.println(correctedtemp);
62.   Serial.println();
63. }
64.  
65. void loop() {
66.   getTemp102();
67.   delay(5000); //wait 5 seconds before printing our next set of readings.
68. }

[Get Code]

 

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Comments

 

Hello, thanks too for this code. I noticed that it does not work for negative temperatures now it is getting colder outside ;-)  To my opinion the problem is in line 37. If the highest bit is 1 also the 4 highest bit of the integer have to be set. I replaced this line with:

    val = firstbyte;
    if ((firstbyte & 0x80) > 0) {
      val |= 0x0F00;
    } 
    val <<= 4;