Bacon Cape

The Bacon Cape is an add-on board meant to give you access to some hardware to help build your understanding of doing basic embedded I/O on BeagleBone.

Board activity

When you visit this page and you have a BeagleBone running BoneScript 0.2.3 or newer with a Bacon Cape attached on your local network or connected to your computer over USB, this display will dyanmically update to reflect the board status. The box color should reflect the color of the RGB LED. The top slider should reflect the status of the push button and turn on the blue LED. The middle slider should reflect the status of the slide potentiometer and adjust the brightness of the green LED. The bottom slider should be adjustable on the page and adjust the brightness of the red LED.

More information about the cape can be found at the eLinux.org Bacon Cape page.

Components

These are the major components of the Bacon Cape.

• S1: a simple push button provides a digital input
  • P8_19: digital I/O connection to BeagleBone
  • Configured as active-low (low when pressed) and uses and external pull-up
• D1: an RGB LED provides an indicator for digital output
  • P9_16: digital I/O connection for BLUE
  • P9_14: digital I/O connection for GREEN
  • P9_42: digital I/O connection for RED
  • Configured as active-high (lit when high)
• R10: a slide potentiometer provides an analog input
  • P9_36: analog input connection to BeagleBone
• U1: shift register feeding a 7 segment display
  • P9_22: CLOCK
  • P9_17: LATCH
  • P9_18: DATA
  • P9_15: CLEAR
  • LED1: connected to shift register output in common anode (active-low) configuration
  • a: last bit shifted out
  • h: first bit shifted out
• U2: I2C EEPROM connected to I2C2

Demo run

Code

// read in BoneScript library
var b = require('bonescript');

// define used pins
var LED_RED = 'P9_42';
var LED_GREEN = 'P9_14';
var LED_BLUE = 'P9_16';
var BUTTON = 'P8_19';
var POT = 'P9_36';
var S_DATA  = 'P9_18';
var S_CLOCK = 'P9_22';
var S_LATCH = 'P9_17';
var S_CLEAR = 'P9_15';

// define other global variables
var s = b.LOW;
var digit = 0;
var segments = [ 0xC0, 0xF9, 0xA4, 0xB0, 0x99,
                 0x92, 0x82, 0xF8, 0x80, 0x90 ];
var stopped = 0;
var started = 0;
var platform = {};

// attach jQuery elements
try {
    $('#slider1').slider();
    $('#slider2').slider();
    $('#slider3').slider();
    $('#led1').css('width', '50px');
    $('#led1').css('height', '50px');
    $('#led1').css('background-color', 'rgb(0,0,0)');
    $("#slider3").bind("slidechange", function(event, ui) {
        updateRed({value:(ui.value/100.0)});
    });
    //$('#runbutton').removeAttr('onclick');
    $('#runbutton').click(runClick);
} catch(ex) {}

// configure pins as inputs/outputs
b.pinMode(S_DATA,  b.OUTPUT);
b.pinMode(S_CLOCK, b.OUTPUT);
b.pinMode(S_LATCH, b.OUTPUT);
b.pinMode(S_CLEAR, b.OUTPUT);
b.pinMode('USR0', b.OUTPUT);
b.pinMode('USR1', b.OUTPUT);
b.pinMode('USR2', b.OUTPUT);
b.pinMode('USR3', b.OUTPUT);
//b.pinMode(LED_RED, b.OUTPUT);
//b.pinMode(LED_GREEN, b.OUTPUT);
//b.pinMode(LED_BLUE, b.OUTPUT);
b.pinMode(BUTTON, b.INPUT);

// initial states
b.digitalWrite('USR0', b.LOW);
b.digitalWrite('USR1', b.LOW);
b.digitalWrite('USR2', b.LOW);
b.digitalWrite('USR3', b.LOW);
b.analogWrite(LED_RED, 0);
b.analogWrite(LED_GREEN, 0);
b.analogWrite(LED_BLUE, 0);
b.digitalWrite(S_DATA,  b.LOW);
b.digitalWrite(S_CLOCK, b.LOW);
b.digitalWrite(S_LATCH, b.LOW);
b.digitalWrite(S_CLEAR, b.HIGH);
//b.attachInterrupt(BUTTON, true, b.CHANGE, handleButton);

// call function to read status and perform updates
function start() {
    console.log('Starting Bacon Cape demo');
    b.getPlatform(onGetPlatform);
}

function onGetPlatform(x) {
    platform = x;
    scheduleNextUpdate();
}

function scheduleNextUpdate() {    
    // test for stop and then schedule next update for 50ms
    if(stopped) {
        started = 0;
        console.log('Stopped Bacon Cape demo');
    } else {
        setTimeout(update, 50);
    }
}

function update() {
    // toggle USR0 LED
    s = (s == b.LOW) ? b.HIGH : b.LOW;
    if(platform.bonescript != '0.2.3') {
        b.digitalWrite('USR0', s, doAnalogRead);
    } else {
        b.digitalWrite('USR0', s, do7SegUpdate);
    }
}

function do7SegUpdate(x) {
    // update 7segment LED
    digit = (digit + 1) % 10;
    
    // shift out the character LED pattern
    b.shiftOut(S_DATA, S_CLOCK, b.MSBFIRST, 
        segments[digit], doLatch);
}

function doLatch() {
    // latch in the value
    b.digitalWrite(S_LATCH, b.HIGH, doLatchLow);
}

function doLatchLow() {
    b.digitalWrite(S_LATCH, b.LOW, doAnalogRead);
}

function doAnalogRead() {
    b.digitalRead(BUTTON, updateBlue);
}

function updateBlue(x) {
    if(typeof x.value == 'undefined') return;
    updateLED({blue:1-x.value});
    b.analogRead(POT, updateGreen);
}

function updateGreen(x) {
    if(typeof x.value == 'undefined') return;
    updateLED({green:1-x.value});
    scheduleNextUpdate();
}

function updateRed(x) {
    if(started) {
        if(typeof x.value == 'undefined') return;
        updateLED({red:x.value});
    }
}

function updateLED(led) {
    if(typeof led.red == 'number') {
        b.analogWrite(LED_RED, led.red);
        this.red = led.red;
    }
    if(typeof led.green == 'number') {
        b.analogWrite(LED_GREEN, led.green);
        this.green = led.green;
    }
    if(typeof led.blue == 'number') {
        b.analogWrite(LED_BLUE, led.blue);
        this.blue = led.blue;
    }
    try {
        if(typeof this.red == 'undefined') this.red = 0;
        if(typeof this.green == 'undefined') this.green = 0;
        if(typeof this.blue == 'undefined') this.blue = 0;
        var rgb = 'rgb(' + Math.round(this.red*255) + ',' + 
            Math.round(this.green*255) + ',' +
            Math.round(this.blue*255) + ')';
        $('#led1').css('background-color', rgb);
        $("#slider1").slider("option", "value", this.blue*100);
        $("#slider2").slider("option", "value", this.green*100);
    } catch(ex) {}
}

function runClick() {
    if(!started) {
        started = 1;
        stopped = 0;
        start();
        try {
            $('#runbutton').html('stop');
        } catch(ex) {}
    } else if(!stopped) {
        stopped = 1;
        var p = '/sys/class/leds/beaglebone:green:usr';
        b.digitalWrite('USR0', b.LOW);
        b.digitalWrite('USR1', b.LOW);
        b.digitalWrite('USR2', b.LOW);
        b.digitalWrite('USR3', b.LOW);
        b.writeTextFile(p+'0/trigger', 'heartbeat');
        b.writeTextFile(p+'1/trigger', 'mmc0');
        b.writeTextFile(p+'2/trigger', 'cpu0');
        b.writeTextFile(p+'3/trigger', 'mmc1');
        try {
            $('#runbutton').html('run');
        } catch(ex) {}
    } 
}

See also

Reference

• Bacon Cape page on eLinux.org

Topics

• BeagleBone expansion headers
• Analog I/O

Related functions

• require
• pinMode
• analogWrite
• analogRead
• digitalWrite
• digitalRead

Where to buy

• Bacon Cape