A Object to Calibrate and Scale Analog Inputs to Engineering Units( In three installments)

**A Object to Calibrate and Scale Analog Inputs to Engineering Units( In three installments)
Part 3:
**
Let’s add two fields to the calibration file, name and units.

var AnalogReadObj1={
  calibrations:[
    {name:"Inlet",units:"psig",pin:'A0',slop­e:10.0,Intercept:5.0},
    {name:"Outlet",units:"psig",pin:'A1',slo­pe:50.0,Intercept:-25.0},
    {name:"Motor",units:"Amps",pin:'A2',slop­e:1.0,Intercept:0.0},
    {name:"Supply",units:"Volts",pin:'A3',sl­ope:1.0,Intercept:0.0},
    {name:"Flow",units:"Liters/minute",pin:'­A4',slope:1.0,Intercept:0.0}
  ]
};//end AnalogReadObj1

function saveCalibration(calibration) {
  var Q;
  var sss=JSON.stringify(calibration);
 if (Q===undefined) {
  Q = E.openFile("Mycalibrations.cal", "w");
  Q.write(sss);
  Q.close();
  Q = undefined;
 }//endif
}//end doLog

saveCalibration(AnalogReadObj1); 
console.log(require("fs").readFileSync("­Mycalibrations.cal"));

The left screen:

>echo(0);
{"calibrations":[{"name":"Inlet","units"­:"psig","pin":"A0","slope":10,"Intercept­":5},
{"name":"Outlet","units":"psig","pin":"A­1","slope":50,"Intercept":-25},
{"name":"Motor","units":"Amps","pin":"A2­","slope":1,"Intercept":0},
{"name":"Supply","units":"Volts","pin":"­A3","slope":1,"Intercept":0},
{"name":"Flow","units":"Liters/minute","­pin":"A4","slope":1,"Intercept":0}]}
=undefined
> 

The code that knits the two objects together and implements a two point calibration.
The calibration is save to the calibration file on the SD card followed by the reading of the calibrated analog inputs in engineering units (EU).
Button 1 on the Espruino board is used to step through the steps. Entering A= selects the channel to calibrate. During the calibration entering B= is used to set the EU values needed for calibration. If A=-1 exits calibration, and proceeds to reading the analog inputs after each press of button1.

var sss=(require("fs").readFileSync("Mycalib­rations.cal")); 
//console.log(sss);

//The constructor for AnalogReadObj
function AnalogReadObj(ARO){
  this.A=JSON.parse(ARO);
}//end AnalogReadObj
//Methods for AnalogReadObj

AnalogReadObj.prototype.saveCalibration=­function() {
  var Q;
  var sss=JSON.stringify(this.A);
  console.log("Saving calibrations");
  console.log(this.A);
 if (Q===undefined) {
  Q = E.openFile("Mycalibrations.cal", "w");
  Q.write(sss);
  Q.close();
  Q = undefined;
 }//endif
};//saveCalibration


AnalogReadObj.prototype.SanalogRead=func­tion(Arg){
    for(var i=0;i in this.A.calibrations;i++){
//      console.log(i,Arg,this.A.calibrations[i]­.pin);
     if(Arg===this.A.calibrations[i].pin){
  return( analogRead(Arg)*this.A.calibrations[i].s­lope+this.A.calibrations[i].Intercept);
     }//endif
    }//next i
    return -99;
};//end SanalogRead

AnalogReadObj.prototype.getName=function­(Arg){
    for(var i=0;i in this.A.calibrations;i++){
//      console.log(i,Arg,this.A.calibrations[i]­.pin);
     if(Arg===this.A.calibrations[i].pin){
      return( this.A.calibrations[i].name);
     }//endif
    }//next i
    return -99;
};//end SanalogRead

AnalogReadObj.prototype.getUnits=functio­n(Arg){
    for(var i=0;i in this.A.calibrations;i++){
//      console.log(i,Arg,this.A.calibrations[i]­.pin);
     if(Arg===this.A.calibrations[i].pin){
      return( this.A.calibrations[i].units);
     }//endif
    }//next i
    return -99;
};//end SanalogRead

AnalogReadObj.prototype.SetAnalog=functi­on(Arg){
    for(var i=0;i in this.A.calibrations;i++)
     pinMode(this.A.calibrations[i].pin, 'analog');
};//end SetAnalog
//end methods for AnalogReadObj

//The constructor for LinRegObj
function LinRegObj(a,nn){
  this.Sx=0;
  this.Sy=0;
  this.Sxy=0;
  this.Sxx=0;
  this.Syy=0;
  this.N=0;
  this.A=a;
  this.NN=nn;
  this.slope=0;
  this.intercept=0;
}//end LinRegObj
//Methods for LinRegObj
LinRegObj.prototype.TakeData=function(y)­{
//LinRegObj.prototype.TakeData=function(­x,y){
  for(i=0;i<this.NN;i++){
    var x=analogRead(this.A.pin);
    this.Sx+=x;
    this.Sy+=y;
    this.Sxy+=(x*y);
    this.Sxx+=(x*x);
    this.Syy+=(y*y);
    this.N++;
  }//next i
};//endTakeData

LinRegObj.prototype.Calculate=function()­{
 this.slope=(this.N*this.Sxy-this.Sx*this­.Sy)/
   (this.N*this.Sxx - this.Sx*this.Sx);
 this.intercept=this.Sy/this.N-(this.slop­e*this.Sx)/this.N;
 this.A.slope=this.slope;
 this.A.Intercept=this.intercept;
};//end Calculate

LinRegObj.prototype.ListChannels=functio­n(T){
  for(var i=0;i in T;i++){
    console.log(i,","+T[i].name+","+T[i].uni­ts);
  }//next i
};//end List Channels
//end LinRegObj methods
var A=0;//used to select channel -1 exits calibration sequence
var B=0;//used to input EU values during calibration

//create an instance of AnalogReadObject using the string data contained in 
//the variable sss
var ScaledAR=new AnalogReadObj(sss);
//console.log(ScaledAR.calibrations);
// setup the pins for analog
ScaledAR.SetAnalog();
//test example calculation
var Q=new LinRegObj(ScaledAR.A.calibrations[0],5);­// 5 samples to take
//SelectChannel();
console.log("Press button on Espruino board to start");
var state=10;

function doButton(){
  if (digitalRead(BTN1) === 1){
    switch (state){
      case 10:
       Q.ListChannels(ScaledAR.A.calibrations);­
       console.log(' ');
       console.log("Select channel by number");
       console.log("Type A=<number>; in left pane");
       console.log("Type A=-1; in the left pane to exit calibrations");
       console.log("Then press button on Espruino board");
       console.log(' ');
       state=20;
      break;

      case 20:
       if(A<0){
        console.log("Exit");
        ScaledAR.saveCalibration();
        state=200;
        return;
       }
       if(A in ScaledAR.A.calibrations){
        console.log("Calibrating ",ScaledAR.A.calibrations[A].name);
        console.log("Apply low value (0.0) input to sensor");
        console.log("Enter the engineering units (EU) by typing in left pane");
        console.log("B=<EU>;");
        console.log("Then press button on the Espruino board");
       }//endif A in Q
       state=30;
      break;

      case 30:
       Q.TakeData(B);
       console.log("Calibrating ",ScaledAR.A.calibrations[A].name);
       console.log("Apply high value (80% FS) input to sensor");
       console.log("Enter the engineering units (EU) by typing in left pane");
       console.log("B=<EU>;");
       console.log("Then press button on the Espruino board");
       state=40;
      break;

      case 40:
       Q.TakeData(B);
       Q.Calculate();
       console.log("Calibrating ",ScaledAR.A.calibrations[A].name);
       console.log("Slope= ",Q.slope);
       console.log("Intercept= ",Q.intercept);
       console.log("Press button on the Espruino board");
       state=10;
      break;
      case 200:
       console.log(' ');
       // Now do a scaled read of pin A0
       console.log(ScaledAR.getName('A0')," A0= ",ScaledAR.SanalogRead('A0').toFixed(2)+­" ",ScaledAR.getUnits('A0'));
       // Now do a scaled read of pin A1
       console.log(ScaledAR.getName('A1')," A1= ",ScaledAR.SanalogRead('A1').toFixed(2)+­" ",ScaledAR.getUnits('A1'));
       // Now do a scaled read of pin A2
       console.log(ScaledAR.getName('A2')," A2= ",ScaledAR.SanalogRead('A2').toFixed(2)+­" ",ScaledAR.getUnits('A2'));
       // Now do a scaled read of pin A3
       console.log(ScaledAR.getName('A3')," A3= ",ScaledAR.SanalogRead('A3').toFixed(2)+­" ",ScaledAR.getUnits('A3'));
       // Now do a scaled read of pin A4
       console.log(ScaledAR.getName('A4')," A4= ",ScaledAR.SanalogRead('A4').toFixed(2)+­" ",ScaledAR.getUnits('A4'));
       console.log("Press button on Espruino board");
      return;

      default:
    }//end switch
  }//end BTN1
}//end doButton

setWatch(doButton, BTN1, true);

The left pane view:

Press button on Espruino board to start
=undefined
0 ,Inlet,psig
1 ,Outlet,psig
2 ,Motor,Amps
3 ,Supply,Volts
4 ,Flow,Liters/minute
 
Select channel by number
Type A=<number>; in left pane
Type A=-1; in the left pane to exit calibrations
Then press button on Espruino board
 A=0;
Calibrating  Inlet
Apply low value (0.0) input to sensor
Enter the engineering units (EU) by typing in left pane
B=<EU>;
Then press button on the Espruino board
>B=0;
=0
Calibrating  Inlet
Apply high value (80% FS) input to sensor
Enter the engineering units (EU) by typing in left pane
B=<EU>;
Then press button on the Espruino board
>B=80;
=80
Calibrating  Inlet
Slope=  100.13897386465
Intercept=  -0.03419722673
Press button on the Espruino board
0 ,Inlet,psig
1 ,Outlet,psig
2 ,Motor,Amps
3 ,Supply,Volts
4 ,Flow,Liters/minute
Xxxxxxxxxxxxxxxxxxxx
A=-1; exits the calibration sequence.
Xxxxxxxxxx
>A=-1
=-1
Exit
Saving calibrations
{
  "calibrations": [
    {
      "name": "Inlet",
      "units": "psig",
      "pin": "A0",
      "slope": 100.13897386465, "Intercept": -0.03419722673 },
    {
      "name": "Outlet",
      "units": "psig",
      "pin": "A1",
      "slope": 50, "Intercept": -25 },
    {
      "name": "Motor",
      "units": "Amps",
      "pin": "A2",
      "slope": 1, "Intercept": 0 },
    {
      "name": "Supply",
      "units": "Volts",
      "pin": "A3",
      "slope": 1, "Intercept": 0 },
    {
      "name": "Flow",
      "units": "Liters/minute",
      "pin": "A4",
      "slope": 1, "Intercept": 0 }
   ]
 }
 
Inlet  A0=  79.94  psig
Outlet  A1=  12.00  psig
Motor  A2=  0.72  Amps
Supply  A3=  0.69  Volts
Flow  A4=  0.82  Liters/minute
Press button on Espruino board

Testing was performed using five 1k resistors wired in series. One end connects to GND and the other end to +3.3V pins. A wire from the analog input pin can then be connected to connections along the resistor chain.

2 Attachments

• doCalibrations1.js
• saveCalibrations1.js