The current revision is "v1", the "RoboThon 2018 edition". Consider this the first BETA version of the board, as of this writing a total of 18 have been built but I've already identified room for improement! Before April of 2018 I'll have tested the second revision with small changes, so you may want to wait before ordering a board from the link below.
On the other hand, if you were given a board to build while at the RoboThon conference, the following will serve as your build guide. (However, please contact me if you have any questions before making your build, andy at andyclymer.com)
The KernTroller PCB v1 is wired up so that the input pins for the "Left" and "Right" buttons are in a "pulled down" configuration, meaning that when the buttons are not pressed the input is connected to ground, and pressing the button down will connect the input pin to the 3.3v power pin.
The Trinket M0 only has three pins that are able to be configured for a capacitive touch input, so it was necessary to be creative to be able to afford five separate touch pads.
The diagram below reveals how it all works: the touch pads "A" and "B" on the left side have their own touch input, but the "Up" and "Down" touch pads on the left hand are really a combination of two pads — pad "A" and "C" for the "Up" button and pads "B" and "C" for the "Down" button. The "Middle" button below the Trinket M0 is connected to the "C" touch pad on its own.
Because of this, the code needs to wait a small moment before detecting which pad was touched — if the touch response was to react immediately when a touch was detected it's completely possile for the "Up" or "Down" buttons to register as the "Middle" or "A" or "B" touch pads if the time wasn't taken to wait until a finger had completely touched both pads.
It's also worth noting that the solder joints on the back of the KernTroller would also respond to touch — it's necessary to cover these to avoid an accidental touch response while holding the KernTroller. (I have some ideas for how to avoid this in the next revision of the board...)
- One KernTroller PCB
- One Adafruit Trinket M0
- Two five-pin 0.1in (2.45mm) spaced header strips (included with the Trinket M0)
- Two 6mm “tactile buttons”
- One USB Micro-B cable
- Optional: Little plastic widget to keep you from touching the pins on the back of the device
- KernTroller PCBs: I'm currently checking for interest on a cheaper run of the second revision of the PCBs, so let me know if you would like to build one!
- Adafruit Trinket M0: Adafruit make a few variations of the Trinket, the most important thing is to purchase the black “Trinket M0” and not the blue “Trinket 5V” or “Trinket 3.3V”! Only the black “M0” variant can work with Python.
- In the United States, the Trinket M0 can be purchased from Adafruit for about $9 each or for a little bit more on Amazon,
- In the Netherlands it can be purchased from Floris or from Kiwi Electronics for about €10,
- In Switzerland it's available from Play-Zone
- 6mm Tactile Buttons: These are very common parts, a bag can be purchased from Adafruit or from Tayda Electronics. If you're having a hard time finding these you can treat them as optional parts, they're not required for the main functionality of the touch pads. These are for the two small “Left” and “Right” buttons at the top of the KernTroller.
- I've laser cut several little plastic widgets that can be attached to the back of the controller to keep your hands from touching the pin connectons on the back — an accidental touch could be read as a button press. Contatct me and I'll put one in the mail, or feel free to laser cut or 3D print your own from the files in the GitHub repo.
- Soldering iron
- Solder
- Clipper tool (AKA “sprue cutters”, “flush cutters”, or “right angle clippers”)
- Isoproply alcohol for cleaning
Collect your components (listed above).
If you purchased PCBs directly from OSH Park, they will likely have small tabs around the edges which are meant to break away. The prototyping service manufactures PCBs ganged up in larger boards with other projects, so you might want to snap these off first and even sand down the edges just a bit.
The Adafruit Trinket M0 should come with one long strip of pin headers, start by breaking it apart to yield the two required five-pin sections.
Fit the pin headers between the KernTroller PCB and the Trinket M0. Solder one header pin to the Trinket M0 and confirm that everything still sits squarely before continue to solder the reamining pins to the Trinket M0. Then, flip everything over and solder the header pins to the Kern>Troller PCB.
Clip the excess length of the pins as closely as you can to the Trinket M0 and Kern>Troller PCB.
Fit the two 6mm tactle buttons. They should only fit in an orientation where their legs are pointed toward the top and bottom of the KernTroller PCB. Turn the PCB over and solder them to attach, and then clip the remaining lenght of their legs as closely to the PCB as possible.
After clipping all of the pins, it might be nice to touch the soldering iron briefly to each solder joint to make it a bit smoother.
Important step: Clean off all of your solder joints with isopropyl alcohol (“rubbing alcohol”) even if you were using "no-clean solder" — the residue is still toxic and should be cleaned off since the circuit board isn't going to live within an enclosure. Don't skip this step!
If you have the “small laser cut plastic widget”, affix it to the back of the board to cover the touch contacts. If you aren't able to obtain this piece, at least cover the contacts with a bit of electrical tape to keep them from shorting if they touch a metal surface.
Final step, before loading any software on the KernTroller, make sure that it has the latest version of CircuitPython installed (many of them will come with a slightly out of date version). It's quick and easy to update, have a look at the instructions in the Software section.