Wednesday, October 31, 2018


Another modular 4x4 experiment

A 4x12 matrix using 3 modular 4x4 matrix boards and powered by a Pro Micro.

The previous 4x4 boards were powered by an Arduino Micro, this one is using a Pro Micro. The Pro Micro has less data pins available so only 3 boards can be connected instead of 4. There are 2 pins left over, I used one (B5) for a backlight circuit like on a Gherkin. The other data pin is left for possible use with a WS2812B strip.

Fully assembled with a top PCB plate. LEDs are powered by a MOSFET and controlled by a PWM enabled data pin (B5).

I also made a plain bottom plate. The plates are held together with solder brides, like on the original 4x4.

Top plate, PCB and bottom plate connected with M2 spacers and screws.

You could just use the PCB and skip the plates. Use PCB mount switches and a piece of wood or aluminum as the base.

The mini USB connector can be installed on any of the 3 boards. The pigtail connects it to the Pro Micro.

If you want LEDs, the MOSFET has to be installed on the first board with the Pro Micro.

I added little nubs that interlock the boards. They may need to be lightly sanded so that they fit into the notches and the boards are flush together.

The edge connectors are in a similar pattern to the original 4x4. Only the top 3 sets of connectors are used for the keyboard matrix. The bottom pair are to pass power, LEDs and the extra data pin. DATA is the extra unused pin and FET is the MOSFET that the LED cathodes on each board connect to.

Gerber files, parts list and a json file for are on git.

JLCPCB PCB price reduction

JLCPCB has lowered their prices.

Says up to 30% off PCB. I checked and a 5 board order of the Luddite PCB was ~10% less then the last time I ordered it. I expect larger orders will see a larger discount. The $2/$5 special for boards under 100mm x 100mm has not changed.

It does not say if this is a limited time thing or if this is a permanent price change.

"The Big Price Drop!
To celebrate the love and support of all our customers, we dropped prices by up to 30% on PCBs, up to 20% on Stencils and up to 10% on shipping."

 Price from old order pictured above, new prices below.

Tuesday, October 23, 2018

Things called "Pro Micro"

Got another "Pro Micro"

The latest one is another black "Pro Micro" that has a Mini USB connector instead of a Micro USB connector. It is #6 in the picture.
  1. A genuine Sparkfun Pro Micro
  2. A typical blue clone Pro Micro
  3. A modified green Pro Micro
  4. The original Black Pro Micro with the larger ATmega32U4 chip
  5. Wider Black Pro Micro with Micro USB connector
  6. Wider (same width as #5) Black Pro Micro with Mini USB connector
  7. Older Pro Micro with Mini USB. These have been around before the green and black Pro Micros
If you are buying a Pro Micro to build a kit with a PCB you should make sure you are getting one that will fit the existing pads on the PCB.

#1-4 are all the same size. They have the same spacing between the two rows of pins, 0.6 inches.

#5-6 are 0.7 inches between the pins. Wider than normal.

#7 is 0.8 inches between the pins. Wider than normal.

#6-7 are considerably longer than normal.

Electrically they are all the same except for #3. If you are handwiring the spacing between the rows would not matter.

Monday, October 15, 2018

Switch Vomit

Luddite with random switches

Wanted to test out the plate. Used up some of the odd left over switches I had laying around.

Clicky, tactile and linear switches. The plate mount stabilizers are a tight fit, but once in place they work perfectly.

The case was recycled from a massdrop KC60. This one had plastic support fins in the center that I had to break off to make room for the Pro Micro. The cheap red case I used previously had no support fins in this area.

Close up of the broken fins. I just snapped off pieces with a pair of pliers.

Close up of the USB pigtail. You will want to make sure the plastic fins are not pinching the wires.

Wednesday, October 10, 2018

Peel-A-Way sockets at

Much cheaper than anywhere else.

$1 for a strip of 82 These are ultra low profile sockets on a removable strip.

I've used these type of sockets on many of my projects. They may be too short for some uses, but good to have on hand at this price.

Peel-A-Way sockets used to socket an Adafruit Feather.

Peel-A-Way socket on the top half and a regular socket on the bottom.

Peel-A-Way socket on the bottom half and a low profile socket on the top.


Keyboard pyramid

Stacked 225, 144, 81, 30, and 16 key keypads in a pyramid.
  • 225 - a 5x5x9
  • 144 - a UNQUADQUAD
  • 81 - SUDOKO, handwired 9x9 matrix.
  • 30 - a keypad I never posted before. It is built from a recycled PCB and 3mm acrylic plates.
  • 16 - a single 4x4x4x4x4
I didn't use a 5x5, It looked better with the wide base of the 5x6 keypad.

Monday, October 8, 2018


Next generation of U2F security keys

There are several new FIDO2 compliant security keys. These will become essential to protecting your online presence. More and more services are supporting their use in 2 factor authentication.

Solo, opensource FIDO2 project

I used the U2FZero open source project to experiment with making my own U2F key. Their second generation key will support FIDO2 and they will also have a version with NFC. You can back their project on kickstarter. These are the cheapest available, if you can wait.

Google Titan bundle

These look a lot like the Feitian U2F keys I have. But these support FIDO2. They sell it as a set of a bluetooth dongle and a NFC USB key. They recommend having 2 keys, one as a backup.

Yubico Series 5 Keys

Yubico keys can do more than U2F and FIDO2, they support additional protocols. The new Series 5 keys add FIDO2 support. There is a lower cost version that only does U2F and FIDO2.

Tuesday, October 2, 2018


Modified 4x4 that can be stacked horizontally and vertically

You can build on the first block either to the right or down. There are headers on all sides of the PCB. You can connect the board with solder bridges or with headers and shunts.

Up to 4 can be connected together. Most of the Tetris shapes can be made, except for the big square. It runs the same firmware as the regular 4x4. Gerber files on git.

All the different ways the boards can be connected. Black square is the board with the controller. The original 4x4x4x4x4 can only be assembled as a horizontal row.

The firmware treats it as a straight 4x16 matrix regardless of layout.