1. Intel Do-It-Yourself Challenge Lab 3: A demo with LED and sensor
Nicolas Vailliet Intel Software

2. Prerequisites and objectives
We assume that:
You are able to download an archive, to unzipped it and run a program under the OS you’re familiar to.
You are able to read pieces of code and comments written in C language.
Our objective are:
Given a Galileo board and a laptop connected on the same network, and the C library and corresponding Makefile, you will be able to compile and run the LedSensor project.
In general,
Our goal is to give you a tool to access to Galileo’s inputs and ouputs quickly and easily. All you need is to know a little bit of C to reuse the Arduino C library for Galileo.

3. Before you start

4. What do you need?
Desktop OS We assume you’re under Microsoft Windows. Linux and Mac users should not have any problem to do the same. Hardware - An Intel Galileo Development Board. - The box comes with power supply and cable. - A Wi-Fi adaptor (N-2200 Mini-PCIe) - A micro SD card (8GB with the full Linux image we provide) Software A SSH client like Putty for Windows. Mac and Linux users only need a terminal. The Arduino library is on the board in ~/labs/ledsensor/c

5. Demo with LED and sensor

6. A simple circuit Resistor is connected to digital port #8.
Bend sensor is between 5V and A0 analog input.
Warning!
Check IOREF Jumper is on 5V position!

7. How does it work? Procedure We blend the sensor.
We read the value on an analogic input.
When a specific value is reached, we turn on the LED.
We turn off the LED when the voltage is under the threshold.
Arduino code
The loop function basically reads a value on the analogic input and decide to turn the LED on or off.
Only 3 Arduino library functions to use:
PinMode,
DigitalWrite,
AnalogRead

8. Arduino version
To copy and paste into your Arduino IDE int sensorPin = A0; // select the input pin for the potentiometer int ledPin = 8; // select the pin for the LED int sensorValue = 0; // variable to store the value coming from the sensor void setup() { Serial.begin(9600); //serial communication at 9600 bits per second pinMode(ledPin, OUTPUT); } void loop() { sensorValue = analogRead(sensorPin); Serial.println(sensorValue); if(sensorValue > 600) digitalWrite(ledPin,HIGH); else digitalWrite(ledPin,LOW); delay(200);

9. Bash version (1/2) Bash version
The script is in ~/labs/ledsensor/bash/ledsensor.sh
It directly uses Linux file system.
#! /bin/bash
# Initializing digital output pin number 8
echo -n "26" > /sys/class/gpio/export
echo -n "out" > /sys/class/gpio/gpio26/direction
echo -n "strong" > /sys/class/gpio/gpio26/drive
echo -n "0" > /sys/class/gpio/gpio26/value
# Initializing analog input A0
echo -n "37" > /sys/class/gpio/export
echo -n "out" > /sys/class/gpio/gpio37/direction
echo -n "0" > /sys/class/gpio/gpio37/value
# Reads the value on A0
sensorvalue=`cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw`

10. Bash version (2/2) Bash version #Infinite loop while true do
#Print values
echo "sensorvalue $sensorvalue "
#if value > 2000 do LED on
if [ $sensorvalue -le 2000 ]
then echo -n "0" > /sys/class/gpio/gpio26/value
else echo -n "1" > /sys/class/gpio/gpio26/value fi
sensorvalue=`cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw`
#Wait 200ms
usleep
done
echo -n "26" > /sys/class/gpio/unexport
echo -n "37" > /sys/class/gpio/unexport

11. Node.js version 1 (1/4) Same project with Node.js
var fs = require('fs'); //use file system module
var fd; //file descriptor
var sensorvalue = 0; //value read from analog input #0
var ledstatus = "off"; //indicate if led is on or off
//Preparing analog inputs A0 and digital output D7
function exportIO(){
//Exporting IO to file system
fd = fs.openSync('/sys/class/gpio/export', 'w');
fs.writeSync(fd,'26'); //D8
fs.writeSync(fd,'37'); //A0
fs.closeSync(fd);
//Setting up direction
fd = fs.openSync('/sys/class/gpio/gpio26/direction', 'w');
fs.writeSync(fd,'out');
fd = fs.openSync('/sys/class/gpio/gpio37/direction', 'w');

12. Node.js version 1 (2/4)
fd = fs.openSync('/sys/class/gpio/gpio26/drive', 'w');
fs.writeSync(fd,'strong');
fs.closeSync(fd);
// Initializing value to 0
fd = fs.openSync('/sys/class/gpio/gpio26/value', 'w');
fs.writeSync(fd,'0');
fd = fs.openSync('/sys/class/gpio/gpio37/value', 'w'); }
Writing a function to turn on the LED
function turnOnLed(){
fs.writeSync(fd,'1');
ledstatus = "on";

13. Node.js version 1 (3/4) Writing a function to turn off the LED
function turnOffLed(){
fd = fs.openSync('/sys/class/gpio/gpio26/value', 'w');
fs.writeSync(fd,'0');
fs.closeSync(fd);
ledstatus = "off"; }
Unexport IO from file system to let it clean after use
function unexportIO(){
fd = fs.openSync('/sys/class/gpio/unexport', 'w');
fs.writeSync(fd,'26'); //D8
fs.writeSync(fd,'37'); //A0
Read the sensor’s output value
function readsensor(){
sensorvalue = fs.readFileSync('/sys/bus/iio/devices/iio\:device0/in_voltage0_raw');

14. Node.js version 1 (4/4) Don’t forget to implement the demo itself…
function ledsensor() {
exportIO();
for(var i=0 ; i < 1000 ; i++){
readsensor();
console.log('A0:'+sensorvalue.toString());
if(sensorvalue > 2000)
turnOnLed();
else
turnOffLed(); }
unexportIO();
Run the function
ledsensor();
GPIO must not be exported before doing exportIO() and vice-versa!

15. Node.js version 2 (1/3) Install galileo-io
Galileo-io is node.js module which simplify IO access from Node.JS. With Galileo-io, you don’t need to manipulate directly the file system (export and unexport stuff).
Install galileo-io with this command on your board:
# npm install galileo-io
Issue: Oops SSL certificate is not valid yet…
If you have an issue with certificates, it’s because your system’s date is not set up properly. Run:
# date –s “01 APR :00:00”

16. Node.js version 2 (2/3) We import galileo-io
var Galileo = require("galileo-io");
var board = new Galileo();
var sensorvalue = "0";
var ledstatus = "off";
A simple call to digitalWrite allows you to control the LED
function turnOnLed(){
board.digitalWrite(8, 1);
ledstatus = "on"; }
function turnOffLed(){
board.digitalWrite(8, 0);
ledstatus = "off";

17. Node.js version 2 (3/3)
A function to activate a listener on analogRead.
NB: The callback function is called each time the value on A0 changes.
function readsensor(){
board.analogRead("A0",function(value){
sensorvalue = value.toString();
});
console.log('A0:'+sensorvalue.toString()); }
We start the demo when the board is ready
board.on("ready", function() {
console.log("Board is ready");
//Setting direction up is also easier with galileo-io
this.pinMode(8, this.MODES.OUTPUT);
ledsensor();

18. C version
C source code (don’t forget header file and optionnaly, the Arduino Serial logger)
#define sensorPin 0  #define ledPin 8 int sensorvalue = 0; void setup(){     pinInit();     pinMode(ledPin, OUTPUT); } void loop(){     for(;;){         sensorvalue = analogRead(sensorPin);         printf("Value: %d\n",sensorvalue);         if(sensorvalue > 600)             digitalWrite(ledPin,HIGH);                 else             digitalWrite(ledPin,LOW);     }  } int main( int argc, char ** argv ) {     interrupt_init();     init(argc, argv);     setup();         loop();   }

19. How to use the Arduino C library
Method
Make a copy of the project
Create your own myfilename.c in ‘src’ folder (copy ledsensor.c)
Edit Makefile and specify myfilename on the second line. Here it was ‘ledsensor’.
If it has not been done before, compile the lib with
# make
Run with
# ./bin/myfilename
Our advice
Instead of recompiling the library, generate your binary only, with:
# make myfilename

20. Next steps
Web LED controller demo Thanks to Node.JS, controlling Galileo from a web interface is easy! Controlling servo motors USB ports on Galileo are useful. Let’s control servo motor! Implement your own projects Want a remote for Galileo? Do it under Android! Another idea? Let’s make it!

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