Per-key RGB for SVT RGB Dumbpad

For the next SVT Dumbpad iteration, I was exploring to add per-key RGB to the 4x4 keys. Here is how it all started.

While doing some research on what LED are commonly used for per-key keyboards, I found this page on Hackaday new-part-day-sk6812-mini-e introducing this new part called SK6812-mini E. This part is unique as it is a surface mounted parts but half of it goes into the PCB cut-outs.

SK6812-mini e dimensions

The timing was perfect as this part (SK6812-mini e) was available from Lazada at a much cheaper price than previously publish at almost 67% lower. I order them and quickly cut the square holes and soldered them once they arrived.

SK6812-mini e front side

SK6812-mini e back side

Thanks for a few other open source keyboard designs, I figured out how to make the cut-out for the footprint for this special parts. As the part is soldered from the back of the PCB but the LED is front facing, I m really really afraid to screw up the pinout. I had to label them clearly ( DI and DO ).

SK6812-mini footprint

After adding the per-key LED with cut-out holes, I do not I have not enough space for the 4 LED WS2812B LED strips and had to re-position all the diodes and use actual WS2812B surface mount parts instead. I only have areas on the top and bottom part of the PCB for the WS2812B LED for the underglow LED.

SVT RGB2 3D Render

As I have NOT added so many LEDs ( 16 + 8 ) to the keyboard before, I was a little nervous about the 5V power consumptions  and add a three way solder bridge to be able to choose between underglow LED, per-key LED or both of them together. To use back the same SVT Dumbpad  firmware, I wire the four LEDs similar as the underglow so I have six parallel LEDs, four facing the top ( per-key LED ) and two facing the bottom (underglow).

The rest of the keyboard remain unchanged but I enlarged the solder pads of the diodes for easy hand soldering. Once the design was done, I usually waited a few more days just in case I think of last minute fixes or new features to add.

SVT RGB2 Dumbpad PCB

Once the PCB arrived, I quickly soldered those per-key LED first without even soldering the rest of the keyboard components. I just use mini grabbers and ran Arduino FastLED to test those LEDs to ensure all the 16 + 8 LED is working fine.

I spend so much time focusing on the SK6812 footprint I neglect the footprint for WS2812B that I have used in my previous product before. It turns out the silkscreen was flipped 180 degree but luckily the wiring was correct, so I de-soldered all the 8 WS2812B and re-solder them 180 degree flipped.

de-soldered WS2812B

SVT RGB2 Dumbpad

Testing per-key RGB LED

Picture without casing

As I also ordered some frosted acrylic, it looks really good on the new per-key RGB LED with diffused RGB lights coming out from the side and bottom.

SVT RGB2 with frosted casing

Below are some video on the SVT RGB2 Dumbpad keyboard.

• https://www.tiktok.com/@stanleyseow/video/6973638416663710978?is_copy_url=0&is_from_webapp=v1&sender_device=pc&sender_web_id=6975161790713005569
• https://www.tiktok.com/@stanleyseow/video/6974607527556205825?is_copy_url=0&is_from_webapp=v1&sender_device=pc&sender_web_id=6975161790713005569

RGB SVT Hotswap and Improvements

RGB SVT hotswap

This is the part 3, further improvements to the keyboard. As I was designing the keyboard, the biggest hurdle for consumer is soldering as not everyone have a soldering iron and tools at home. 

Kailh hotswaps

With this reason, I decided to move away from a soldering solution to a hotswap solution using Kailh hotswap PCB socket. As I have already design the top PCB plates for holding the switches, I just need to change the footprint to a hotswap only. I also moved the diode to the bottom layer for easier soldering or repairs.

Kailh PCB Socket

PCB with Kailh hotswap soldered

For this version, I will most likely sell them pre-soldered and qmk firmware flashed instead of in a kit form, so the customer can get add switches only without any soldering needed.

Extra RGB LEDs

Another "extra" feature, if you look closely at the end of the WS2812B LED RGB strip, you can actually add more RGB LED and extend it beyond the keyboard.

Extend WS2812 RGB

Just solder a wire to the middle DATA pin and extend the RGB strip outside of the keyboard. Just make sure you supply enough 5V power if the WS2812 RGB strip is very long.

For the firmware side, the following need to be change to reflect the number of RGB LEDs installed.

#define RGBLED_NUM 4

Change this number to the additional number of LED you added to the end of the RGB strip.

Final keyboard picture with Kailh PCB hotswap sockets with top support plates on acrylic enclosure.

Summary Links

• Kailh hotswap PCB socket
• WS2812B LED
• Part 1 https://arduino-for-beginners.blogspot.com/2020/11/building-4x4-mechanical-keyboard-with.html 
• Part 2 https://arduino-for-beginners.blogspot.com/2020/12/qmk-flashing-and-coding-svt-rgb-4x4.html
• Part 4 https://arduino-for-beginners.blogspot.com/2021/06/per-key-rgb-for-svt-rgb-dumbpad.html