Vellamy's blog about Arduino: USB Host Shield & Sensors

Arduino USB Host Shield & Sensors

ABSTRACT

In this activity I’ve used the Arduino USB Host Shield to send sensor data from Arduino to an Android Device. The communication is full duplex, Arduino send data to Android and Android send data to Arduino.

The USB Host Shield is a board that uses the USB host controlled chip MAX3421E. I’ve used the SparkFun board [1]. This version takes its power from the 'Vin' pin on your Arduino. Power from that pin is regulated to both 5V and 3.3V on the shield. For this reason, it is necessary an extra charger.

There are several libraries for USB Host Shield, I know two: “Adb.h” and “AndroidAccessory.h”. In [2], there are explained a lot of examples with the Abd library but the drawback of use it is that you need Android programming knowledge for developing your application. In this case I’ve used the AndroidAccessory library because I wanted to program the Android App with Processing. In [3], you can download a tool for Processing to compile code for the latest Android OS and upload it to phones and tablets.

Figure 1: Usb host connected to the phone

MATERIALS

1 x Arduino board

1 x USB cable

1 x Humidity sensor 808H5V5

1 x Temperature sensor MCP9700A

1 x Pot 10KΩ

1 x Pot 4K7Ω

1 x Res. 1KΩ
1 x Res. 330Ω
2 x Res. 10KΩ

1 x Photoresistor

1 x Temperature and humidity sensor: DHT03

1 x Green led

1 x Small buttons

1 x proto-board

1 x Charger

1 x Android Phone

Wires, pins, solder lead, etc…

Figure 2: Arduino host shield and the others components

DEVELOPMENT

In the next figure you can see the schematic of how I’ve connected to Arduino the sensors and the other things.

Figure 3: Schematic

The Arduino code is in the Appendix 1. From [1] you can download all the libraries that you need for the USB Host Shield. If you are using the SparkFun board you must assure that in the file Max3421e_constans.h has the correct definition of some pins. In my case, I had to modify this pins:

#define MAX_INT 9

#define MAX_GPX 8

#define MAX_RESET 7

The library for the digital humidity and temperature sensor DHT03 is in [4]. The Processing code is in the Appendix 3.

Figure 4: Android application

RESULTS

The best way to see the results is to watch it in a video. In this video you are going to see how Arduino send data to the phone.

Sometimes, when you push the button “OUT”, Arduino detects two pulsations because the Processing code don’t have any kind of anti debounce method.

PROPOSALS OF IMPROVEMENT

Send the data obtained by the USB Host Shield via 3G or via Wi-Fi to another device.

REFERENCE

[1] https://www.sparkfun.com/products/9628
[2] http://labs.arduino.cc/ADK/Index
[3] http://mitchtech.net/
[4] http://playground.arduino.cc/Main/DHTLib

APPENDIX 1

Arduino main code:

#include <Arduino.h>

#include <Max3421e.h>

#include <Usb.h>

#include <AndroidAccessory.h>

#include <dht.h>

#include <Bounce.h>

#include "floatToString.h"

dht DHT;

float data[6];

int boton=3,led=5,dhtpin=6,temp=0,luz=0,humedad=0,temperatura=0,moisture=0,pot1=0,pot2=0;

char cadena[80];

char tempC[10];

char luzC[10];

byte pulsacion[2];

byte msg[2];

AndroidAccessory acc("pruebaUSB3",

"pruebaUSB3",

"1.0",

"http://www.android.com",

"0000000012345678");

// Instantiate a Bounce object with a 5 millisecond debounce time

Bounce bouncer = Bounce( boton,5 );

void setup()

{

Serial.begin(9600);

pinMode(led, OUTPUT);

pinMode(boton, INPUT);

digitalWrite(led, LOW);

digitalWrite(boton, HIGH); // enable the internal pullups

attachInterrupt(1, sendBoton, FALLING);

delay(100);

acc.powerOn();

delay(5000);

}

void loop()

{

//Lectura de entradas analógicas y digitales

pot1=analogRead(A0);

delay(10);

pot2=analogRead(A1);

delay(20);

data[2] = analogRead(A4) * .004882814;

data[2] = (data[2] - 0.5) * 100;//0 degree begins in 500mV

//temp=(int)data[2];

floatToString(tempC,data[2],0);

delay(20);

data[3] = analogRead(A5);

//luz = (int)data[3];

floatToString(luzC,data[3],0);

delay(10);

data[6]=analogRead(A3)* 4.882814;

data[6]=(data[6]-800)/31;

moisture = (int) data[6];

delay(10);

int chk = DHT.read22(dhtpin);

data[4] = DHT.humidity;

humedad=(int)data[4];

delay(10);

data[5] = DHT.temperature;

temperatura=(int)data[5];

delay(10);

bouncer.update();

//Enviar datos al dispositivo android

if (acc.isConnected())

{

acc.read(msg, sizeof(msg), 1);

Serial.println((char)msg[0]);

if((char)msg[0]=='a')

{

//Encender y apagar el led

if(digitalRead(led)) digitalWrite(led, LOW);

else digitalWrite(led, HIGH);

msg[0]='b';

}

delay(10);

sprintf(cadena,"%d,%d,%sC,%s,%uH,%dH %dC,",pot1,pot2,tempC,luzC,moisture,humedad,temperatura);

Serial.println(cadena);

acc.write(cadena,sizeof(cadena));

delay(1000);

}

else

{

Serial.println("No conectado");

delay(2000);

}

void sendBoton(void)

{

pulsacion[0]=1;

if (acc.isConnected()) acc.write(pulsacion,1);

else Serial.println("Incapaz de conectar");

delay(10);

pulsacion[0]=0;

}

AndroidAccessory(const char *manufacturer,

const char *model,

const char *description,

const char *version,

const char *uri,

const char *serial);

void powerOn(void);

bool isConnected(void);

int read(void *buff, int len, unsigned int nakLimit = USB_NAK_LIMIT);

//NAK means no communication error

int write(void *buff, int len);

*/ digitalWrite(ledPin, HIGH); // Toggle status LED

delay(1000);

digitalWrite(ledPin, LOW); // Toggle status LED

}

APPENDIX 2

FloatToString.h code:

// floatToString.h

// Tim Hirzel

// tim@growdown.com

// March 2008

// float to string

// If you don't save this as a .h, you will want to remove the default arguments

// uncomment this first line, and swap it for the next. I don't think keyword arguments compile
// in .pde files

//char * floatToString(char * outstr, float value, int places, int minwidth=, bool rightjustify) {

char * floatToString(char * outstr, float value, int places, int minwidth=0, bool rightjustify=false) {

// this is used to write a float value to string, outstr. oustr is also the return value.

int digit;

float tens = 0.1;

int tenscount = 0;

int i;

float tempfloat = value;

int c = 0;

int charcount = 1;

int extra = 0;

// make sure we round properly. this could use pow from <math.h>, but doesn't seem worth the import

// if this rounding step isn't here, the value 54.321 prints as 54.3209

// calculate rounding term d: 0.5/pow(10,places)

float d = 0.5;

if (value < 0)

d *= -1.0;

// divide by ten for each decimal place

for (i = 0; i < places; i++)

d/= 10.0;

// this small addition, combined with truncation will round our values properly

tempfloat += d;

// first get value tens to be the large power of ten less than value

if (value < 0)

tempfloat *= -1.0;

while ((tens * 10.0) <= tempfloat) {

tens *= 10.0;

tenscount += 1;

}

if (tenscount > 0)

charcount += tenscount;

else

charcount += 1;

if (value < 0)

charcount += 1;

charcount += 1 + places;

minwidth += 1; // both count the null final character

if (minwidth > charcount){

extra = minwidth - charcount;

charcount = minwidth;

}

if (extra > 0 and rightjustify) {

for (int i = 0; i< extra; i++) {

outstr[c++] = ' ';

}

// write out the negative if needed

if (value < 0)

outstr[c++] = '-';

if (tenscount == 0)

outstr[c++] = '0';

for (i=0; i< tenscount; i++) {

digit = (int) (tempfloat/tens);

itoa(digit, &outstr[c++], 10);

tempfloat = tempfloat - ((float)digit * tens);

tens /= 10.0;

}

// if no places after decimal, stop now and return

// otherwise, write the point and continue on

if (places > 0)

outstr[c++] = '.';

// now write out each decimal place by shifting digits one by one into the ones place and writing
//the truncated value

for (i = 0; i < places; i++) {

tempfloat *= 10.0;

digit = (int) tempfloat;

itoa(digit, &outstr[c++], 10);

// once written, subtract off that digit

tempfloat = tempfloat - (float) digit;

}

if (extra > 0 and not rightjustify) {

for (int i = 0; i< extra; i++) {

outstr[c++] = ' ';

}

outstr[c++] = '\0';

return outstr;

}

APPENDIX 3

Processing code:

import cc.arduino.*;

ArduinoAdkUsb arduino;

String inString;

byte pulsador=0;

String A="0",B="0",C="0",D="0",E="0",F="0";

int index=0;

boolean i=false;

char a='a',b='b';

boolean botonPulsado = false;

color botonAmarillo= color(255,255,0);

color botonGris=color(150);

int puntoX=380,puntoY=630,diametro=100;

void setup()

{

arduino = new ArduinoAdkUsb( this );

if ( arduino.list() != null ) arduino.connect( arduino.list()[0] );

orientation( PORTRAIT );

textSize(40);

stroke(4);

strokeWeight(8);

}

void draw()

{

fill(0);

//RECIBIR EL MENSAJE DE ARDUINO

if ( arduino.isConnected())

{

int bytesDisponibles = arduino.available();

if(bytesDisponibles> 3 )

{

inString="";

for(int n=0;n<bytesDisponibles;n++) inString=inString+arduino.readChar();

index = inString.indexOf(',');

A=inString.substring(0,index);