BMP085 I2C pressure/temperature sensor graphing demo

Demo run restore

var b = require('bonescript');
var i2c = '/sys/class/i2c-adapter/i2c-1/';
b.writeTextFile(i2c + 'new_device', 'bmp085 0x77');
var graphDataSize = 50;
window.graphData = new Array(graphDataSize);
var canvas = document.getElementById("canvas1");
var processing = new Processing(canvas, sketchProc);
setInterval(readTemp, 100);

function readTemp() {
    b.readTextFile(i2c + '1-0077/temp0_input', updateGraph);    
}

function updateGraph(x) {
    for(var i=0; i<graphDataSize-1; i++) {
        window.graphData[i] = window.graphData[i+1];
    }
    window.graphData[i] = (parseInt(x.data, 10)/200.0)-0.7;
    processing.redraw();
}

function sketchProc(p) {
    p.size(500, 300);

    // variables referenced elsewhere
    window.height = p.height;

    // variables that might get updated
    window.rangeLow = 0;
    window.rangeHigh = 1;
    window.scaleY = window.height /
        (window.rangeHigh - window.rangeLow);

    // local variables
    var stepX = p.width / (graphDataSize - 1);
    var centerY = window.height / 2;

    p.noLoop();
    p.draw = function() {
        // erase background
        p.background(224);

        // draw axis
        p.stroke(25);
        p.strokeWeight(1);
        p.line(0, centerY, p.width, centerY);

        // draw graph
        p.stroke(0);
        p.strokeWeight(3);
        //p.line(0, centerY+1, p.width, centerY+1);
        var lastX = 0, nextX = 0, lastY, nextY;
        for(var point in window.graphData) {
            nextY = ((window.rangeHigh -
                window.graphData[point]) * scaleY);
            if(point !== 0) {
                p.line(lastX, lastY, nextX, nextY);
                lastX += stepX;
            }
            nextX += stepX;
            lastY = nextY;
        }
    };
}

Build and execute instructions

• Disconnect your board from power (including USB)
• Connect BMP085 GND to P9_1
• Connect BMP085 VCC to P9_3
• Connect BMP085 SCL to P9_19
• Connect BMP085 SDA to P9_20
• Reapply power and refresh this page before running the demo code

See also

Topics

• BeagleBone expansion headers

Related functions

• require
• readTextFile
• writeTextFile