ARDUINO AS A KEYBOARD
ABSTRACT
In this activity I’ve made a little circuit with Arduino that simulates
to be a keyboard. At the beginning I was looking for a way to send data between
Arduino and the tablet without using the USB host module. Then, I realized that
this task would be very straightforward if I cheated the tablet or the PC
simulating as Arduino were a Human Interface Device.
The aim of this circuit is to send the information of temperature and
humidity to the tablet through a USB cable. Searching a solution in Internet, I
found this web [1]. This web is extremely useful if you are an Arduino fan.
As you can see in the Figure 1, the design is like an Arduino shield. It
has temperature and humidity sensors, one led, four small buttons and the rest
of the components for send the data through the USB cable.
The circuit sends a little message when you push one of button. One
message is the temperature and other message is the humidity. Basically the led
does not do anything, it is collocated there only for debugging. The other
device can be a tablet or a PC. It does not work with iPad because they are fascists
and force you to buy expensive stuff for everything.
 |
| Figure 1: The circuit developed as a shield above the Arduino board. |
MATERIALS
1 x Arduino board
2 x USB cable AM/BM
1 x Humidity sensor
1 x Temperature sensor
4 x Res. 10KΩ
2 x Res. 68 Ω
1 x Res. 2K2Ω
1 x Res. 330 Ω
2 x Diode Zener 3V6, 0.50W
4 x Small buttons
1 x 4 pins connector or Usb
female type B
1 x proto-board
Wires, pins, solder lead, etc…
DEVELOPMENT
The schematic of the hardware is in the following
picture:
 |
| Figure 2: Schematic of the circuit. |
Before starting to program the Arduino it is necessary
to download the USBkeyboard library from [3], that it is a link of the web of
the project [2]. In my case I modified the file “usbconfig.h” for using other
digital pins. I changed the lines 33 and 68. The example used the digital outputs
5 and 4 but I’ve used the pins 6 and 7.
#define
USB_CFG_DMINUS_BIT 7 // Before: 4
#define
USB_CFG_PULLUP_BIT 6 // Before: 5
The Arduino code is in the Appendix 1. The functions for getting the temperature and the humidity are in the file “Sensors.h” that are in the Appendix 2.
RESULTS
The results can be watched in the next video:
Sorry for the quality of the video.
REFERENCE
[1] http://www.practicalarduino.com/projects/virtual-usb-keyboard
[2] http://code.rancidbacon.com/ProjectLogArduinoUSB
[3] http://www.obdev.at/products/vusb/download.html
PROPOSALS OF
IMPROVEMENT
Use Arduino as a HID mouse.
Develop HID pedals.
APPENDIX 1
Arduino main code:
#include
#include
"UsbKeyboard.h"
#include
"Sensors.h"
#define BUTTON_A 8
#define BUTTON_B 9
#define BUTTON_C 10
#define BUTTON_D 11
// Use the on-board
LED as an activity display
int ledPin = 13;
// If the timer isr
is corrected
// to not take so
long change this to 0.
#define
BYPASS_TIMER_ISR 1
int
humidity=0,temperature=0;
void setup()
{
Serial.begin(9600);
// Set the button pins to inputs
pinMode (BUTTON_A, INPUT);
pinMode (BUTTON_B, INPUT);
pinMode (BUTTON_C, INPUT);
pinMode (BUTTON_D, INPUT);
// Enable the CPU's internal 20k pull-up
resistors on the button
// inputs so they default to a
"high" state
digitalWrite (BUTTON_A, HIGH);
digitalWrite (BUTTON_B, HIGH);
digitalWrite (BUTTON_C, HIGH);
digitalWrite (BUTTON_D, HIGH);
#if
BYPASS_TIMER_ISR
// disable timer 0 overflow interrupt (used
for millis)
TIMSK0&=!(1<
#endif
}
#if
BYPASS_TIMER_ISR
void
delayMs(unsigned int ms) {
/*
*/
for (int i = 0; i < ms; i++) {
delayMicroseconds(1000);
}
}
#endif
void loop()
{
int val=0;
UsbKeyboard.update();
if (digitalRead(BUTTON_A) == LOW)
{
UsbKeyboard.sendKeyStroke(KEY_H);
UsbKeyboard.sendKeyStroke(KEY_E);
UsbKeyboard.sendKeyStroke(KEY_L);
UsbKeyboard.sendKeyStroke(KEY_L);
UsbKeyboard.sendKeyStroke(KEY_O);
UsbKeyboard.sendKeyStroke(KEY_SPACE);
UsbKeyboard.sendKeyStroke(KEY_W);
UsbKeyboard.sendKeyStroke(KEY_O);
UsbKeyboard.sendKeyStroke(KEY_R);
UsbKeyboard.sendKeyStroke(KEY_L);
UsbKeyboard.sendKeyStroke(KEY_D);
UsbKeyboard.sendKeyStroke(KEY_ENTER);
#if
BYPASS_TIMER_ISR // check if timer isr
fixed.
delayMs(20);
#else
delay(20);
#endif
}
if (digitalRead(BUTTON_B) == LOW)
{
temperature=Temperatura();
UsbKeyboard.sendKeyStroke(KEY_T);
UsbKeyboard.sendKeyStroke(KEY_E);
UsbKeyboard.sendKeyStroke(KEY_M);
UsbKeyboard.sendKeyStroke(KEY_P);
UsbKeyboard.sendKeyStroke(KEY_E);
UsbKeyboard.sendKeyStroke(KEY_R);
UsbKeyboard.sendKeyStroke(KEY_A);
UsbKeyboard.sendKeyStroke(KEY_T);
UsbKeyboard.sendKeyStroke(KEY_U);
UsbKeyboard.sendKeyStroke(KEY_R);
UsbKeyboard.sendKeyStroke(KEY_E);
UsbKeyboard.sendKeyStroke(KEY_SPACE);
val= 29 + temperature/10;
if(val!=0) UsbKeyboard.sendKeyStroke(val);
val= 29 + temperature%10;
if(val==29) UsbKeyboard.sendKeyStroke(39);
else UsbKeyboard.sendKeyStroke(val);
//UsbKeyboard.sendKeyStroke(KEY_ENTER);
#if
BYPASS_TIMER_ISR // check if timer isr
fixed.
delayMs(20);
#else
delay(20);
#endif
}
if (digitalRead(BUTTON_C) == LOW)
{
humidity=Humedad();
UsbKeyboard.sendKeyStroke(KEY_H);
UsbKeyboard.sendKeyStroke(KEY_U);
UsbKeyboard.sendKeyStroke(KEY_M);
UsbKeyboard.sendKeyStroke(KEY_I);
UsbKeyboard.sendKeyStroke(KEY_D);
UsbKeyboard.sendKeyStroke(KEY_I);
UsbKeyboard.sendKeyStroke(KEY_T);
UsbKeyboard.sendKeyStroke(KEY_Y);
UsbKeyboard.sendKeyStroke(KEY_SPACE);
val= 29 + humidity/10;
if(val!=0) UsbKeyboard.sendKeyStroke(val);
val= 29 + humidity%10;
if(val==29) UsbKeyboard.sendKeyStroke(39);
else UsbKeyboard.sendKeyStroke(val);
//UsbKeyboard.sendKeyStroke(KEY_ENTER);
#if BYPASS_TIMER_ISR // check if timer isr fixed.
delayMs(50);
#else
delay(50);
#endif
}
if (digitalRead(BUTTON_D) == LOW)
{
UsbKeyboard.sendKeyStroke(KEY_L);
UsbKeyboard.sendKeyStroke(KEY_E);
UsbKeyboard.sendKeyStroke(KEY_D);
#if
BYPASS_TIMER_ISR // check if timer isr
fixed.
delayMs(100);
#else
delay(100);
#endif
digitalWrite(ledPin, HIGH); // Toggle
status LED
delay(1000);
digitalWrite(ledPin, LOW); // Toggle status
LED
}
}
APPENDIX 2
Sensors.h code:
static
int temperaturePin = 5;//14 Analog input 0
static
int humidityPin=4;//15 Analog input 1static int moisturePin=2;//Analog input 2
int
Temperatura(void)
{
//the analog pin the TMP36's Vout (sense) pin
is connected to the resolution is 10 mV / degree centigrade.
//(500 mV offset) to make negative
temperatures an option
float temperature=analogRead(temperaturePin) *
.004882814;//converting from a 0 to 1023 digital range
// to 0 to 5 volts (each 1 reading equals ~ 5
millivolts.Example: 5:1024=0.004882814
temperature = (temperature - .5) * 100;//0
degree begins in 500mV
Serial.print("Temperature: ");
Serial.print(temperature,0);
Serial.println("\260C");
return(int(temperature));
}
int Humedad (void)
{
//5V=1024;5000mV/1024=4.882814mv por unidad
float
humidity=analogRead(humidityPin)* 4.882814;
humidity=(humidity-800)/31;//Conversion of
milivolts to humidity
Serial.print("Air humidity: ");
Serial.print(humidity,0);
Serial.println("%");
return(int(humidity));
}
