Blog of Wei-Hsiung Huang: HID Keyboard

This post is the second part of How to turn Arduino Uno into HID Keyboard tutorial. The first part can be found here.

To test the HID Keyboard, I want to use the "Random Key/Random Delay" code from http://mitchtech.net/arduino-usb-hid-keyboard/ because of its simplicity and there is no wiring involved.

/* Arduino USB HID Keyboard Demo
* Random Key/Random Delay
*/

uint8_t buf[8] = {
0 }; /* Keyboard report buffer */

void setup()
{
Serial.begin(9600);
randomSeed(analogRead(0));
delay(200);
}

void loop()
{
int randomChar = random(4, 130);
long randomDelay = random(1000, 10000);

delay(randomDelay);

buf[2] = randomChar; // Random character
Serial.write(buf, 8); // Send keypress
releaseKey();
}

void releaseKey()
{
buf[0] = 0;
buf[2] = 0;
Serial.write(buf, 8); // Release key
}

To use the code, follow the below procedure (assuming the ATMega16U2 has "Arduino-usbserial-uno.hex" in it):

1. Copy and past the above code into Arduino IDE;

2. Compile and upload the code to Arduino Uno;

3.. Follow the instruction in my previous post to burn the "Arduino-keyboard-0.3.hex" into ATMega16U2;

4. Unplug the USB cable and plug it back in;

5. Launch a word editing program (MS-Word, UltraEdit, etc.) and wait to see random character appears at random interval.

When you are done with the test, follow the instruction in my previous post to burn the "Arduino-usbserial-uno.hex" back into ATMega16U2 then unplug the USB cable and plug it back to make the board a normal Arduino Uno again.

Reference

Arduino USB HID Keyboard
http://mitchtech.net/arduino-usb-hid-keyboard/

This is the first of a two parts series. This part is to provide a brief overview of HID concept and how to prepare and turn an Arduino Uno into a HID device (in this case, a HID Keyboard).

The 2nd part will be dealing with the coding of an Arduino sketch to send keystrokes to the connected PC over the USB port and some other stuff. The 2nd part can be found here.

Brief Overview

The Arduino USB HID keyboard is implemented by sending a 8-byte long "Keyboard Report Buffer" via the USB that connects the PC and the Arduino.

The format of the Keyboard Report Buffer is as follow.

The format of the Modifier Keys (Byte 0) is as follow.

As for keycode 1 ~ 6, they can be found in the Keyboard Scan Codes in the reference section of this post.

Preparing the Arduino and the needed firmware and tools

Note, the instructions below are for Arduino Uno and MS-Windows 8.1.

1. Check the Arduino board for its version and whether the USB Serial chip used is supported by the DFU tool.

Mine is R3 (no need to modify it)

If yours is R1, please follow the instruction here to modify it.

This board is using MEGA16U2

MEGA16U2 is on the support list

2. Download and save the "Arduino-usbserial.hex" in a safe location. This firmware needs to be in atmega16u2 for burning sketch unto the Arduino board using Arduino IDE and USB cable.

Here is the download link.
https://dl.dropboxusercontent.com/u/1816557/Arduino-usbserial-uno.hex

Note,

I think there is a missing Arduino-usbserial.hex in at the below github site.

https://github.com/arduino/Arduino/tree/master/hardware/arduino/avr/firmwares/atmegaxxu2/arduino-usbserial

3. Download a DFU Programmer from http://www.atmel.com/tools/flip.aspx.

Since I already have Java Run Time installed on my PC, I downloaded the one without Java Run Time.

4. Download the Keyboard HID firmware "Arduino-keyboard-0.3.hex" from here and save it to a safe location. After this firmware is written into atmega16u2, the Arduino Uno board will be viewed as a USB keyboard when it's plugged into a PC.

Burning the firmware into atmega16u2

1. Put the atmega16u2 in DFU (Device Firmware Update) mode by briefly shorting the 2 leftmost ICSP headers next to the USB port.

2. Install the ATmega16U2 DFU driver.

Note, the driver needs to be installed for Flip to communicate with ATmega16U2 on the Arduino Uno board.

On the computer, the driver "atmel_usb_dfu.inf" can be found under C:\Program Files (x86)\Atmel\Flip 3.4.7\usb.

3. Launch Flip. Select "Device", then select ATmega16U2 from the list.

4. Left click on the "Select a Communication Medium", left click on USB, left click on Open. The USB:ON indication on the lower right hand corner indicates Flip is now connected to ATmega16U2.

5. Go to File, Load HEX File, and select the Hex file to be written into ATmega16U2.

In this case, I choose to burn the "Arduino-keyboard-0.3.hex".

6. Click on Run to erase the existing firmware (Earse), write the new firmware (Program), and verify the written firmware (Verify) in ATmega16U2.

7. Unplug the USB cable that connects the Arduino Uno and the PC then plug the cable back in again. Go to Device Manager and there is now a HID Keyboard Device under "Keyboard".

Below is the Device Manager screen when a normal Arduino Uno is plugged in. Note that there is no HID Keyboard Device under Keyboard and an Arduino Uno is shown under COM & LPT

To burn the USB Serial firmware back to ATmega16U2 (turn the HID Keyboard Device back to a normal Arduino Uno board), simply repeat step 1 to 7 above except step 5. In step 5, select the previous saved "Arduino-usbserial-uno.hex" instead of "Arduino-keyboard-0.3.hex".

After "Arduino-usbserial-uno.hex" is written into ATmega16U2, close Flip, remove USB cable then plug it back in. The Windows OS will detect it as a new device and look for its driver. Very soon it will recognize it as an Arduino Uno and uses the already installed driver to support it. After that, the board is ready for uploading sketch via the Arduino IDE again.

Note,

Remember to short the 2 leftmost ICSP headers next to the USB port before launching Flip.

After shorting the pins, there will be an Atmel USB Devices in the Device Manager and no HID Keyboard Device. The ATmega16U2 is now ready to be flashed with new firmware.

Reference

Keyboard Scan Codes

The tables below are from P53 ~ P59 of the "USB HID Usage Tables". This document can be downloaded at http://www.usb.org/developers/hidpage/Hut1_12v2.pdf.