Datasheet Help - LSM9DS1

[putabirdyonit]

Hello,

I am working on a IoT project and have everything done BUT 1 conversion. It is really driving me mad.

Quick preface, I need to read the ambient temperature in celsius from this 9DOF board (LSM9DS1). I know that the board was not designed for accurate temperature. I don't need accuracy I just need to be able to put a flame, finger, or blowdryer on it and see the temperature climb. I am having a really hard time figuring out this conversion. I can't tell if the board is giving me bad data or if my conversion is wrong. Whats worse, I need to do this is Node.js.

What is the conversion formula for this sensor in NodeJS?

function convert(word) {
    return celsius
}

I am reading 1 word from 0x15
Here are some pictures from the datasheet.
Any help is welcomed.

[wildbill]

It looks like you need to read the other register too. If you're only getting 0x15, you're missing the high bits.

[wvmarle]

An Arduino is programmed in C++. Nodejs, is that something to do with javascript? If so, it has no obvious link with Arduinos - where does the Arduino come in play in this project?

[putabirdyonit]

wildbill, I am reading a word. The function is something like i2c_bus.readWord(address, register). Word is 2 bytes. It should read low and high together. I can read each byte too. Either works for me. Its the whole "right justified" "2s complement" conversion that confuses me. I did take a low level assembly course but its been a while and I forget. The closest I have gotten is (sudo code)...

read(0x15) => low
0101 0101 --> 85

read(0x16) => high
1111 1111 --> 255

"Right justified" so LSB on the right?

low & high together => (high, low)
1111111101010101 --> 65365

2s complement
-171?

---

wvmarle, this is indeed not for a arduino but for a raspberry pi. I figured with forum would still be a good resource as I am asking about the conversion which should be similar regardless of language.

[wvmarle]

On an Arduino, in C++, I'd do something like:

uint16_t result = read(0x16) << 8 | read(0x15);

to combine two bytes into a single 16-bit unsigned integer. Note that this works in part as the Arduino's C++ compiler defaults to 16-bit width. Other compilers may behave differently, and on an Arduino you have to be careful doing this with values greater than two bytes.

[putabirdyonit]

wvmarle,

So that is exactly how I also do it in C++. Does that method handle the "2s Compliment" aspect as well? I might just be able to import a low-level library into my Node.js project that simulates uint16_t.