Espruino WiFi temperature display

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  • Just thought I'd post this up... Basically it's an Espruino WiFi board with a DS18B20 attached, but it sets itself up as an access point.

    When you access the server's IP, you get a webpage which displays an image which is the contents of the LCD display at that point.

    It's a bit of a hack, but basically I created a black and white bitmap of the right size with an image editor and saved it, then just copied out the first few bytes which are the header. I could then just re-render the image into another Graphics object (the one for the display has the pixels in a strange order) and send it over HTTP.

    Hope that's some use - it could be a great way to serve up graphs and stuff like that.

    require("Font8x12").add(Graphics);
    
    A5.write(0); // GND
    A7.write(1); // VCC
    A6.write(1); // Turn on the backlight
    var g; // Define g globally, so that it can be used by other functions
    var sensor;
    var apState = "Connecting";
    var wifi;
    var temperature;
    
    var history = new Float32Array(84*2);
    
    function onBmp( res) {
      // BMP header
      res.write("BM\xc2\2\0\0\0\0\0\0\x82\0\0\­0l\0\0\0T\0\0\x000\0\0\0\1\0\1\0\0\0\0\0­@\2\0\0\23\13\0\0\23\13\0\0\2\0\0\0\2\0\­0\0BGRs\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\­0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\­0\0\0\0\0\0\0\0\0\0\0\0\2\0\0\0\0\0\0\0\­0\0\0\0\0\0\0\0\0\0\0\0\xff\xff\xff\0");­
      // re-render screen image into correctly sized memory buffer
      var g = Graphics.createArrayBuffer(88+8,48,1,{ms­b:true});
      g.setRotation(2,1);
      g.setBgColor(1);
      g.setColor(0);
      g.getWidth = function() { return 84; };
      g.clear();
      draw(g);
      // output the memory buffer
      res.end(E.toString(g.buffer));
    }
    
    function onPageRequest(req, res) {
      var a = url.parse(req.url, true);
      if (a.query && "led" in a.query)
        digitalWrite(LED1, a.query["led"]);
      if (a.pathname=="/") {
        res.writeHead(200, {'Content-Type': 'text/html'});
        res.end('<html><body><img src="img.bmp" width="336" height="192"><br/>Turn LED <a href="?led=1">on</a> or <a href="?led=0">off</a></body></html>');
      } else if (a.pathname=="/img.bmp") {
        onBmp(res);
      } else {
        res.writeHead(404, {'Content-Type': 'text/plain'});
        res.end("404: Page "+a.pathname+" not found");
      }
    }
    
    function onInit() {
      clearInterval();
      clearWatch();
      // Setup SPI
      var spi = new SPI();
      spi.setup({ sck:B1, mosi:B10 });
      // Initialise the LCD
      g = require("PCD8544").connect(spi,B13,B14,B­15, function() {
        // When it's initialised, clear it and write some text
        g.clear();
        g.drawString("Loading...",0,0);
        // send the graphics to the display
        g.flip();
        setInterval(onTimer, 1000);
      });
      sensor = require("DS18B20").connect(new OneWire(B4));
      sensor.getTemp(function (temp) {
        history.fill(temp);
      });
      // Wifi
      wifi = require("EspruinoWiFi");
      apState = "Connecting";
      wifi.startAP("EspruinoTemperature", {authMode:"wpa_wpa2",password:"12345678"­}, function() {
        apState = "192.168.4.1";
        console.log("Connected...");
        require("http").createServer(onPageReque­st).listen(80);
      });
    }
    
    function draw(g) {
      // draw text
      g.clear();
      g.setFontBitmap();
      g.drawString(apState,0,0);
      g.drawString("Temperature",0,8);
      g.setFont8x12();
      g.drawString(temperature,g.getWidth()-g.­stringWidth(temperature),2);
      // draw graph
      history.forEach(function (val, i) {
        g.setPixel(i*g.getWidth()/history.length­, 
                   E.clip(30+(val-history[0]), 8,47));
      });
    }
    
    function onTimer() {
      sensor.getTemp(function (temp) {
        temperature = temp;
        // shift on    
        history.set(new Float32Array(history.buffer, 4),0);
        // set values
        history[history.length-1] = temperature;
        draw(g);
        // send to screen
        g.flip();
      });
    }
    
  • And a picture...


    1 Attachment

    • espruino_wifi_demo_sml.jpg
  • Nice.

    Another way of doing the graphic for the browser, would be to use the xbm format, which uses C declarations to define the graphics, so you output the width and height and an array.

  • Yeah, I wondered about that - but sadly it seems most web browsers are now having support removed :( en.wikipedia.org/wiki/X_BitMap#s­upport

    I should really turn this into a module - it could be quite handy.

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Espruino WiFi temperature display

Posted by Avatar for Gordon @Gordon

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