francescomecca.eu/_posts/2016-07-05-arduino_keyboard.md

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2016-07-06 07:49:02 +02:00
---
title: Arduino Uno as HID keyboard
date: 2016-07-05
author: pesceWanda
layout: post
categories:
- PesceWanda
tags:
- Arduino
- HID arduino
- mechanical keyboard
- programming
- arduino uno
---
2016-07-07 02:05:21 +02:00
Turin is the hometown of Arduino. I have been at the [fablab](http://fablabtorino.org/) multiple times but I had to come all the way to America to get my hands on a simple Arduino Uno.
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For 60$ I bought a cheap (but still good!) mechanical keyboard by Qisan, a clone of the Arduino Uno and a USB host shield.
Given that is 3 years since I have been using a dvorak layout and it's a pain to change layout on every machine that you have to use.
You can imagine that given this three pieces of hardware together I put together an hardware key mapper for the keyboard.
I have never had experience with Arduino before but it was not that difficult to make it do simple things like blinking the led or send signal through to a serial monitor.
It took me half an hour to wear down all my excitement: the USB Host Shield library broke all the compatibility with the similar project I found wandering online.
In particular [this blog](http://hunt.net.nz/users/darran/) has the most precious information and the guy wrote a HID driver that allows the Uno to be seen as a HID device.
It was a noob error but I didn't checked the various arduino alternatives and I discovered late that just a few have the HID capabilities that would make this work easier. I should have bought and Arduino Due or Leonardo maybe.
Also, the various guides about flashing with a dfu tool are specific to older models of the Uno and it took me some time to figure the name of the new components so that I could flash a new firmware.
## A small journey in the Arduino world
It feels pretentious to write a little guide for this kind of work, given also the fact that I have roughly 10 hours of experience with the Arduino. But the other resources are really outdated so I hope this piece can be useful to someone out there.
All the files I have used today are on [my repos](http://francescomecca.eu:3000/pesceWanda/arduino_HID_keyboard) and I included also an outdated version of the USB Host Shield library that I used.
The original code from this [blog post](http://hunt.net.nz/users/darran/weblog/c6f35/Arduino_USB_Keyboard_Passthrough.html) works like a charm but just as a simple passthrough.
It was not difficult at all to examine the code:
during each loop of the iteration a char array gets read from the shield and if it is contains information Arduino with the Serial.Write method send the data to the host.
The buffer array is a simple array of length 8 and the first two positions are reserved. In particular the first one represent the various modifier keys.
The dvorak layout has the same pairs as the US layout but eventually I got used to having the '@' where at the same place of 'Q' (qwerty) and '"' over the '2'.
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Also, I am an avid vim user (I should thank Simone Basso for that) and I swapped some keys on the new 65 keys keyboard.
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The modifier bit at the beginning of the array came in handy for my code.
An hardware key remapper is a simple but long switch C statement but I decided to consider also the modifier bit: in this way certain keys like the Window (UGH!) key is mapped to a different layer of keys.
I got all the codes for the HID events [here](http://www.freebsddiary.org/APC/usb_hid_usages.php).
The process of flashing the code on the Uno goes like this:
* write the looping code;
* push it to the Arduino using the IDE;
* shortcircuit the board so that it goes in DFU mode;
* flash the .hex HID firmware;
* try your code;
* repeat until it's right.
![Everything fits in one picture](/wp-content/uploads/2016/IMG_20160706_011304.jpg)
## Flashing the firmware
The firmware is in my repo but I got it from (here)[http://hunt.net.nz/users/darran/weblog/a6d52/Arduino_UNO_Keyboard_HID_version_02.html].
The tool I used to flash it is dfu-programmer (version 0.62).
Every time you want to flash a new firmware the Arduino must be put in DFU mode (you can see the difference with lsusb).
To do that simply create a shortcircuit using a small metal wire on the two pins near the reset button and a led will blink.
This [video](https://www.youtube.com/watch?v=E8XyRwXQr8Q) shows the method briefly (no real need for a jumper).
The commands are the following and there is no risk to brick the Uno:
```
dfu-programmer atmega16u2 erase
dfu-programmer atmega16u2 flash Arduino-keyboard-0.2.hex
dfu-programmer atmega16u2 reset
```
After each flashing the device needs to be disconnected once. Of course you can flash the original firmware back. It is included in my repo or on the official ones.
![Arduino and the shield](/wp-content/uploads/2016/IMG_20160706_011143.jpg)
That's it, as you can see is not difficult at all. The worst part is gathering the various info that are left dormant in blogs or forums.