New joint DHT11/DHT22 module

Hi,

It's come up in another thread that the existing DHT11 & 22 modules aren't that fast or memory efficient. There's been a pull request for a multipurpose module, but it's still slower than it could be, and doesn't work in a backwards-compatible way with DHT11.

I don't have a DHT22 here so can't test, but maybe someone else could take a look at this and see if it works on all the various different module types, or whether we need a few more tweaks?

// Sensor object constructor
function HT(device, pin) {
  this.device = device;
  this.pin = pin;
}

// sensor query method...
/** read sensor as either...
  read(callback);
  read(callback,number_of_tries); - default=3
  */
HT.prototype.read = function (cb,n) {
  if (!n) n=3;
  var d = ""; 
  var ht = this;
  pinMode(ht.pin); // set pin state to automatic
  digitalWrite(ht.pin,0);
  this.watch = setWatch(function(t) {
    d+=0|(t.time-t.lastTime>0.00005);
  }, ht.pin, {edge:'falling',repeat:true} );
  setTimeout(function() {pinMode(ht.pin,'input_pullup');},1);
  setTimeout(function() {
    clearWatch(ht.watch);
    delete ht.watch;
    var cks = 
        parseInt(d.substr(2,8),2)+
        parseInt(d.substr(10,8),2)+
        parseInt(d.substr(18,8),2)+
        parseInt(d.substr(26,8),2);
    if (cks&&((cks&0xFF)==parseInt(d.substr(34,8),2))) {
      var o = { raw:d };
      if (ht.device=="DHT11") {
        o.rh = parseInt(d.substr(2,8),2);
        o.t = parseInt(d.substr(18,8),2);
      } else {
        o.rh = parseInt(d.substr(2,16),2)*0.1;
        o.t = parseInt(d.substr(19,15),2)*0.2*(d[16]-0.5);
      }
      cb(o);
    } else {
      if (n>1) setTimeout(function() {ht.read(cb,--n);},500);
      else cb({err:true, raw:d});
    }
  },6);
};

// Test with
var dht = new HT("DHT11",A8);
dht.read(print);

I can then put it into a HTxx module, and can reference that from existing DHT11/22 modules to provide a seamless upgrade for everyone already using them.