SPI question

I tried out the code and it sort of works!

The only problem with including trtn.temp and trtn.fault in the same variable is the way the chip works. It supplies a 14 bit word that has temperature and fault information. Therefore when the fault flag is raised it still gives a temperature, just the wrong temperature. I included the if else statement in the earlier code to account for this. Maybe someone can suggest a way to accomplish with the trtn.temp and trtn.falut included in the same variable.

{"temp":2047.75,"fault":1,
"faultstring":"No probe detected"
}

see the example above where no probe is detected yet the temperature is reported back as 2047.75C.

Ideally I think what is needed for simple example temperature measurement is the correct temperature or the fault condition.

Updated on my site. Code is:

exports.connect = function(spi,cs) {
  return new MAX31855(spi,cs);
};

function MAX31855(spi,cs) {
  this.spi=spi;
  this.cs=cs;
}

MAX31855.prototype.getTemp = function () {
  var d = SPI1.send("\0\0\0\0",this.cs); 
  if (d.charCodeAt(1) & 1)  {
    var trtn = {fault: (d.charCodeAt(3) & 7)};
    switch (trtn.fault) {
      case 1:
        trtn.faultstring="No probe detected";
        break;
      case 3:
        trtn.faultstring="Probe shorted to Ground";
        break;
      case 4:
        trtn.faultstring="Probe shorted to VCC";
        break;
    }
    return trtn;
  } else {
    return {temp: (d.charCodeAt(0)<<6 | d.charCodeAt(1)>>2)*0.25, fault: 0};
  }
};

SPI1 should be this.spi :-)

I tested and this code works. Just need to change one last item that Possmann stated above and its ready to be added to the modules. I spent some time working with I2C over the weekend and can provide a couple of other temperature modules to post soon.

Great! It's already done! https://github.com/espruino/EspruinoDocs/blob/master/devices/MAX31855.js

It'll go live next time I update the website...

It is really a good idea, to return an error message string instead of an error code? I guess thois could safe some memory and performance. What do you think?

I'm not sure it's such a big worry here. One nice improvement would be to define the error strings in an array: trtn.faultstring=[,"No probe detected",,"Probe shorted to Ground","Probe shorted to VCC"][trtn.fault]