--- 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 --- Turin is the hometown of Arduino. I have been at the [fablab](http://fablabtorino.org/) multiple times but I am more of a software guy. I had to come all the way to America to get my hands on a simple Arduino Uno. 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 But the other resources are really outdated so I hope this piece can be useful to someone out there.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have used today are on [my repos](http://francescomecca.eu:3000/pesceWanda/arduino_HID_keyboard) and I included also an outdated version of the USB Host Shield library that I used.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'. 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. 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.