danieleln/micro-keyboard

Arduino-powered, 8-key HID keyboard

micro-keyboard

micro-keyboard is an 8-key, Arduino-powered HID keyboard.

Out of the eight buttons, the top-left one switches between different pages:

• Page 1 emulates keys ESC, BACKSPACE, ENTER, LEFT_ARROW, DOWN_ARROW, UP_ARROW, RIGHT_ARROW (in order from left to right, top to bottom)
• Page 2 emulates keys F1 to F7
• Page 3 emulates keys F8 to F14

Emulated keys can be easily customized.

The Arduino Micro built-in LED blinks when switching between pages. It blinks a number of times equal to the page number.

To understand why I built this pretty weird project, see the paragraph some backstory. For more details on the technical side, see the paragraph implementation notes.

Some backstory

I have an issue with my laptop. For some reason, it doesn't recognize the built-in keyboard before booting the OS (it's probably a driver issue, but that's not my area of expertise). However, it does recognize external keyboards I have at home.

It's never been much of an issue. I rarely have to enter the BIOS when I'm not at home. However, a couple of weeks ago I had to install PSPICE on my laptop for the Electromagnetic Compatibility course I'm taking at the university. Unfortunately, that is a Windows-only software (my main OS is Ubuntu). I went for a dual boot cause it's a ten years old laptop and running Windows on a VM was a bit too heavy.

Back to the issue. At home, I code with an external monitor and keyboard. So, I didn't discover the issue till it was too late: I can't control GRUB with the built-in keyboard. GRUB just boots the first OS on the list.

The two "immediate" solutions are:

• Boot in whichever the first OS on the list is. Change the boot order. Reboot the system. While it might work, it would take a good 20 minutes or so on my laptop.
• Carry an external keyboard to the university. It doesn't fit in my backpack.

So, I decided to build a tiny custom "keyboard" I could easily carry around.

Implementation notes

While there are much better ways to implement a keyboard emulator, here are the reasons why I chose to code it this way.

First of all, I had to use a third-party HID library cause the built-in Keyboard.h library was also not recognized at boot.

This was a last-minute solution. Thus, my main goal was to get it done quickly. I already had around the Button.hpp class (I wrote it back in high school), so I took advantage of it. In fact:

• It's scalable: introducing new buttons is easy (in case I'll ever need more of them). With interrupts, it's a bit less immediate, plus not all pins feature interrupt capabilities.
• Abstraction: the library hides all the nitty-gritty details of how buttons are debounced, which (hopefully) increases the readability.
• NO Need For Speed: the particular case study doesn't require the keyboard to have the fastest possible time response (it's not meant for gaming!). Interrupts don't provide much benefit in this case.

Also, the LED lighting is a bit controversial: while the rest of the code is non-blocking, I used the (blocking) delay() function to pulse the LED. Reasons are:

• Those delays are anyway pretty fast.
• Eventually missing a key press is not an issue for this type of application.
• Implementing a non-blocking solution is more time-consuming and not worth for such a simple task.