Mini USB Keyboard With a $7 Microcontroller

Make a keyboard that uses a microcontroller to send usb keypresses, which interfaces with AutoHotKey, a Windows application for creating applications and macros.

AutoHotKey can be used with your original keyboard with no need for an additional keyboard. This supplementary device isn't for everyone, but some of the uses include:

simplifying annoying hotkeys to the push of a single button
creating special controllers for games / interfaces
creating program specific tasks, like using each button to save out a different filetype in an application

The AutoHotKey software can assign just about anything to the press of a button:

launching applications
multi step commands that can be done with the keyboard
simplifying cumbersome shortcuts
launching a specific web url
inserting snippets of text

This was just an experiment for me, but I have found it to be useful for many things, so I thought I'd share. I am not experienced in circuit design or arduino programming, but this worked for me and maybe it can help with your projects. I did not see a lot of information about using the trinket, so I thought that making this available for people to see could be helpful. Feel free to comment on any improvements that could be made.

Step 1: Supplies

Materials / parts:

Adafruit Trinket microcontroller
Mx Cherry key sampler
small perf board
resistors: 1k(x4), 100k(x2)
solder
wire

Tools:

soldering iron
hack saw
pliers

Step 2: Modifying the Enclosure

I used a mx cherry keyboard sample that I had, but anything with multiple switches could be used for this: game controllers, numeric keypads, or just switches on a pcb.

Grooves will need to be cut in the separating walls of the base. this is so we can run connecting wires through. I used pliers to snap out some of the dividing plastic between the top and bottom keys, to run a few more wires through.

Step 3: Making the Circuit

I started by soldering the full length wire going to one of the inputs that was isolated on the end. then I soldered in the resistors and connections between buttons, then finally snaked in the last full length wire around everything else.

It might take some maneuvering to keep the components out of the way so it sits flat. Then solder the trinket and resistors to the perf board, and lastly connect to the buttons.

Step 4: Trinket Arduino Code

Here is the code I used, you might have to tweak the input values to get the best results. I just replaced the F keys with letters and tested in notepad.

#include 

const int sensorPin = 3;
const int sensorPin2 = 2;
int sensorValue = 0;
int sensorValue2 = 0;
void setup()
{
   pinMode(sensorPin, INPUT);
   pinMode(sensorPin2, INPUT);
// start USB stuff
  TrinketKeyboard.begin();
}
void loop() {
   sensorValue = analogRead(sensorPin);
   sensorValue2 = analogRead(sensorPin2);
    TrinketKeyboard.poll();
    
   if( sensorValue >= 615 and sensorValue <= 625 ) {  
    TrinketKeyboard.pressKey(0, 0);
   }
   if( sensorValue >= 700 and sensorValue <= 800 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F4);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0,0);
    delay(300);
   }
  if( sensorValue >= 670 and sensorValue <= 700 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F6);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   if( sensorValue >= 655 and sensorValue <= 660 ) { 
    TrinketKeyboard.pressKey(0,KEYCODE_F7);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   if( sensorValue >= 650 and sensorValue <= 655 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F8);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   if( sensorValue2 >= 650 and sensorValue2 <= 800 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F9);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
  if( sensorValue2 >= 600 and sensorValue2 <= 650 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F10);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   if( sensorValue2 >= 580 and sensorValue2 <= 600 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F11);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   if( sensorValue2 >= 560 and sensorValue2 <= 579 ) {  
    TrinketKeyboard.pressKey(0,KEYCODE_F12);
    // this releases the key (otherwise it is held down!)
    TrinketKeyboard.pressKey(0, 0);
    delay(300);
   }
   }

minikeyboard.ino
Download

Step 5: AutoHotKey Code

SetTitleMatchMode, 2
Hotstring to enter time stamp in document
; F6 and F7 keys always have the same function regardless of the active program
F6::
Run, "C:\Windows\Sysnative\SnippingTool.exe" ; opens snipping tool
return
#IfWinActive, Snipping Tool ; if snipping tool is open, the same button will close it
F6:: 
{ WinClose Snipping Tool }
return
#IfWinActive
F7::
FormatTime, CurrentDateTime,, yyyyMMdd ; inserts the current date in a specified format
SendInput %CurrentDateTime%
return
; F8 and F9 keys function varies by the active program
#IfWinActive, Program Manager ; functions if desktop is active
F8::
run taskmgr.exe ; open task manager
return
F9::
IfWinExist Google Chrome ; open Chrome or maximize window if open already
WinActivate, Google Chrome 
else
run "C:\Program Files (x86)\Google\Chrome\Application\chrome.exe"
return
#IfWinActive
#IfWinActive, Chrome ; Chrome specific functions
F8::
Send, ^+{Tab} ; go left a tab
return
F9::
Send, ^{Tab} ; go right a tab
return
#IfWinActive
#IfWinActive ahk_class CabinetWClass ; windows explorer specific functions
F8::
Send, !{Up} ; go up a folder level
return
F9::
Send, ^n ; opens a new window
return
#IfWinActive

Step 6: Customization

Using a separate usb device lets you customize the buttons for your needs. There are a whole bunch of custom key caps available online to use for a custom USB input device.