Lasers!

A bit of an update to this... I bought this laser module, which contains a driver IC: http://www.amazon.com/dp/B00HHHVV2K/ref=­pe_385040_30332200_TE_item

It's a bit pricey (£100), but I thought that if I was going to do it then I might as well do it properly!

I then connected an Espruino up to an old Plotmate A3M plotter that I had hanging around. These are just dumb plotters - internally there's the mechanics, a power supply, drive transistors, and some circuitry that appears to serve no useful purpose apart from to make it difficult to use.

The connections on the back are easy. There's a 20 pin connector, and all of one side of it is ground. On the other side there's:

Pin 1,2,3,4 - X stepper
Pin 5,6,7,8 - Y stepper
Pin 9 - Pen down (inverted)
Pin 10 - Axis end stop hit (inverted)

I connected these right down the side of the Espruino board (B13,B14,B15,C4,C5,C6,C7,C8,C9,C10).

After a huge amount of messing around, I found out the following on how the steppers are driven:

motorx = [B13,B14,B15,C4] (0,1,2,3)
Pin 1 (common) -> 4 (coil A), 5 (coil a)
Pin 2 (common) -> 3 (coil B), 6 (coil b)


1324
AaBb
0 -> 0110
1 -> 0101
2 -> 0100
3 -> 0101

4 -> 1010
5 -> 1001
6 -> 1000
7 -> 1001

8 -> 0010
9 -> 0001
10 -> 0000
11 -> 0001

12 -> 1010
13 -> 1001
14 -> 1000
15 -> 1001

step order = [14,13,9,3,2,0,8,4]


motory = [C5,C6,C7,C8] (4,5,6,7)
Pin 1 (common) -> 5 (coil A),6 (coil a)
Pin 2 (common) -> 3 (coil B),4 (coil b)

1324
AaBb

0 -> 1010
1 -> 0010
2 -> 1001
3 -> 0001

4 -> 0110
5 -> 0110
6 -> 0101
7 -> 0101

8 -> 1000
9 -> 0000
10 -> 1001
11 -> 0001

12 -> 0100
13 -> 0100
14 -> 0101
15 -> 0101

step order = [8,0,1,4,12,14,3,10];

And finally: here's the code so far that's needed to drive the plotter - it'll home the axes, and draw a circle...

var pins = [B13,B14,B15,C4,C5,C6,C7,C8,C9,C10];
var ENDSTOP = pins[9]; // negated
// pins[8] = !pen down
// pins[9] = !axis hit
var motorx = pins.slice(0,4);
var xsteps = [14,13,9,3,2,0,8,4];
var motory = pins.slice(4,8);
var ysteps = [8,0,1,4,12,14,3,10];
var motorxoff = 10;
var motoryoff = 9;


function Stepper(pins, pattern, offpattern) {
  this.pins = pins;
  this.pattern = pattern;
  this.offpattern = offpattern;
  this.pos = 0;
}

Stepper.prototype.setHome = function() {
  this.pos = 0;
};

Stepper.prototype.stop = function(turnOff) {
  if (this.interval) {
    clearInterval(this.interval);
    this.interval = undefined;
  }
  if (turnOff && this.offpattern)
    digitalWrite(this.pins, this.offpattern);
};

Stepper.prototype.moveTo = function(pos, milliseconds, callback, turnOff) {
  pos = 0|pos; // to int
  if (milliseconds===undefined)
    milliseconds = Math.abs(pos-this.pos)*10;
  this.stop(turnOff);
  if (pos != this.pos) {
    var stepper = this;
    this.interval = setInterval(function() {
      // remove interval if needed
      if (stepper.pos == pos) {
        stepper.stop(turnOff);
        if (callback)
          callback();
      } else {
        // move onwards
        stepper.pos += (pos < stepper.pos) ? -1 : 1;
        // now do step
        digitalWrite(stepper.pins, stepper.pattern[ stepper.pos & (stepper.pattern.length-1) ]);
      }
    }, milliseconds / Math.abs(pos-this.pos));
  } else {
    if (callback)
      setTimeout(callback, milliseconds);
  }
};

var x = new Stepper(motorx, xsteps, motorxoff);
var y = new Stepper(motory, ysteps, motoryoff);

function home(callback) {
  x.moveTo(50,undefined,function() {
    y.moveTo(50,undefined,function() {
      setWatch(function() {
        y.stop();
        y.setHome();
        y.moveTo(50,undefined,function() {
          setWatch(function() {
            x.stop();
            x.setHome();
            y.moveTo(0,undefined,callback,true);
          }, ENDSTOP, {edge:falling, repeat:false});
          x.moveTo(-10000);
      });
      }, ENDSTOP, {edge:falling, repeat:false});
      y.moveTo(-10000);
    });
  });
}

function setPenDown(down) {
  digitalWrite(pins[8], !down);
}

function draw(positions, callback) {
  function moveTo(p, callback) {
    var dx = x.pos - p[0];
    var dy = y.pos - p[1];
    var d = Math.sqrt(dx*dx+dy*dy);
    var time = d*50; // speed
    x.moveTo(p[0],time, undefined, false);
    y.moveTo(p[1],time, callback, false);
  }
  function moveToNext() {
    print(positions.length);
    if (positions.length) {
      moveTo(positions.shift(), moveToNext);
    } else {
      setPenDown(false);
      x.stop(true);
      y.stop(true);
      callback();
    }
  }
  
  if (positions.length) {
    moveTo(positions.shift(), function() {
      setPenDown(true);
      moveToNext();
    });
  } else {
    callback();
  }
}

function circle() {
  var positions = [];
  for (var i=0;i<20;i++) {
    var t = Math.PI*2*i/20;
    positions.push([(1+Math.cos(t))*200,(1+M­ath.sin(t))*200]);
  }
  draw(positions, function() {
    print("done");
  }); 
}

The laser is currently attached to a large aluminium heatsink, and then to the pen carriage. Hopefully I'll make laser control automatic soon, but for now it's done manually. It kind of works...

1 Attachment