The EmojiPad is a USB Keypad in the form of a soldering kit. To allow a beginner to assemble the kit it has the following features:

  • 100% Through-Hole Construction
    • No SMD Soldering Skills Needed!
  • Easy to read instructions for assembling the PCB
  • Well marked silkscreen

After the kit has been completed, the USB Keyboard will have the following features:

  • 16 Keys
    • Mapped to emoticons by default
    • Reprogrammable via Arduino
  • Illuminated Keys
    • Keys are backlit using LEDs, operation of LEDs is selectable using Arduin0



An ATmega328 is used as the microcontroller for this device. This device was chosen to do it's availability in a DIP package, and the amount of support from the maker community.


16 Cherry MX switches are used in a standard keyboard matrix configuration. 1N4148 diodes are used on each of the switches to prevent masking of keystrokes from occurring. The schematic for the Keypad is shown below.

Keypad LEDs

To control all of the LEDs, they are Charliplexed. This method involves using the ability for microcontrollers to tristate the I/O to allow for n pins to drive n^2-n LEDs. The schematic for the LEDs is shown below.


Since the ATmega328 does not contain a USB peripheral, the V-USB library from Objective Development will be used to allow the device to show up as a USB HID Keyboard.

The implementation within Arduino leverages the work done by RancidBacon on his USBKeyboard library, this was then modified to work with the specific hardware configuration, as well as the USB VID and PID needed on this project.



The case will consist of two laser cut pieces of bamboo and the required hardware needed to mount the bamboo pieces and PCBA together. The complete BOM for the case is:

  • 1 - Top Case (Laser cut Bamboo)
  • 1 - Bottom Case (Laser cut Bamboo)
  • 4 - 20mm M3 Male-Female Standoffs
  • 4 - M3 Acorn Nuts
  • 8 - M3 10mm Screws
  • 4 - 2mm M3 Spacers
  • 3 - M3 Nuts


The Keycaps are currently blank, white keyboard caps which are available via Taobao. Options for these keycaps from the United States are extremely expensive (~$1 a cap) and I am still looking for other sourcing options. To add graphics to the caps, vinyl decals can be applied.