ADS1115 analog gain signal module - how to run it with espruino?

If gain is set to 4096 (accoriding to Table 3 on page 13 of TI ADS1115 datasheet:

• measurement range is from -4.096V..4.095999V
  
• values are (always) -32768..0..32767
  (1 value unit equals to 0.000125V)
  
  

Therefore, for 2.048V you should get a value of 16384, which is at half in the positive half of the value range... 0..16384..32767

6.144/32768 = 0.0001875 - about 50% off from the above calculated 4.096 related 0.000125 value, therefore, I 'assume', the gain setting is not working correctly... it took 6.144 because:

I did look at the 'last' 'module' code and my language concious did not 'like' property names of the GAINS object that are pure numbers: lines 57..62 - even though it obviously works partially, because you do not mention the built-in error (...! in GAINS) has not caugth on). BUT: ... | 4096 is | 2 ^ 12 or | 0b0001'0000"0000'0000 or | 0x1000 - just sets bit 12 (counting from 0) outside of the PGA_MASK... not what you want. Obviously, it did not mess up, at least not totally. Since it does not throw an error it clears all (gain mattering) bit(s) - see PGA_MASK - and that ets the gain to 2/3: -6.144..0..+6.144 volts, which explains the 6.144 / 32768 term that worked for you. Make the following changes, and things should just work as expected:

Lines 56..63:

var GAINS = {
  G6144 : CONFIG.PGA_6_144V,  // +/-6.144V range = Gain 2/3
  G4096 : CONFIG.PGA_4_096V,  // +/-4.096V range = Gain 1
  G2048 : CONFIG.PGA_2_048V,  // +/-2.048V range = Gain 2 (default)
  G1024 : CONFIG.PGA_1_024V,  // +/-1.024V range = Gain 4
  G512 : CONFIG.PGA_0_512V,  // +/-0.512V range = Gain 8
  G256 : CONFIG.PGA_0_256V,  // +/-0.256V range = Gain 16;
};

Lines 71..75:

function ADS1X15(i2c) {
  this.i2c = i2c;
  this.addr = 0x48;
  this.gain = 2048;
}

Lines 80..84:

ADS1X15.prototype.readRegister = function(reg) {
  this.i2c.writeTo(this.addr, reg);  
  var d = this.i2c.readFrom(this.addr, 2);
  return ((d[0] << 8) | d[1]) / 32768;  // returning value in volts
};

Lines 85..89:

// set the gain, with a value in mv (6144, 4096, 2048, 1024, 512 or 256). The value is the full swing, so 256 = +/- 0.256v
ADS1X15.prototype.setGain = function(gain) {
  if (!(("G" + gain) in GAINS)) throw new Error("Gain "+gain+" not found");
  this.gain = gain;
};

Lines 97 and 98:

  // Set PGA/voltage range
  config |= GAINS["G"+this.gain];

Usage:

I2C1.setup({ scl: B6, sda: B7 });
var ads = require("ADS1X15").connect(I2C1);
ads.setGain(4096); 
setInterval(function(){
  ads.getADC(3, function(val) {
      console.log(v.toFixed(3) + "V");     
  });
},3000);

Now there are a few memory saving options that can be applied...

a) Throw GAINS away. There is already an object in place that holds the gains: CONFIG... therefore, lines 87. and 98. each become 2 lines and read:

   var g = "PGA_" + ("0" + this.gain + " V").substr(-5); 
   if (!(g.substr(0,5) + "_" +  g.substr(5)) in CONFIG)) throw new Error("Gain "+gain+" not found");

  var g = "PGA_" + ("0" + this.gain + " V").substr(-5); 
  config |= CONFIG[g.substr(0,5) + "_" +  g.substr(5)];

b) Simplify the gains part in CONFIG like you had it in GAINS and it forming the property names becomes inline instead of an extra composition line for string g:

Lines 18..23:

PGA_6144mV: 0x0000,  // +/-6.144V range = Gain 2/3
PGA_4096mV: 0x0200,  // +/-4.096V range = Gain 1
PGA_2048mV: 0x0400,  // +/-2.048V range = Gain 2 (default)
PGA_1024mV: 0x0600,  // +/-1.024V range = Gain 4
PGA_512mV: 0x0800,  // +/-0.512V range = Gain 8
PGA_256mV: 0x0A00,  // +/-0.256V range = Gain 16

    if (!("PGA_" + this.gain + "mV") in CONFIG)) throw new Error("Gain "+gain+" not found");

    config |= CONFIG["PGA_" + this.gain + "mV"];

Btw, I wondered why the config is set all the times, is it not sufficient to set it once? Could make it sense to have 4 configs (3, or 2 in - 1 or 2 - diff mode)?