What's the smallest board that can be a controller?

[cribbit]

Teensy or arduino pro micro are pretty small but are a touch big for what I'm trying to do.

I only need 16 pins

For reference I'm trying to fit the controller inside the (eventually hollowed out) square on the edge of



I'm not sure if it's even possible to fit all the circuitry on a board that small. I'm also considering custom making a controller PCB that could take advantage of the small area next to the square, or double side the SMD components to put them in a smaller footprint.

I also need a good way to get all the cols to wire back to the controller without making a rats nest of wire. Still trying to figure out what the thinnest wire I can use is, I think I can put 2-3 cols in each between-row channel if I make the channel just right.

[regack]

There are a couple of things that stand in the way of making things smaller.  Placement of the USB port, reset switch (make this a set of pads you jump, instead of a switch), the size of the package of the controller, say TQFP vs QFN, and the size/spacing of your solder pads for your wiring.   The 2.54 pitch through-hole spacing on the teensy and the like just takes up... well... space... but if you're going to solder SMD bits anyway, maybe go with 1.27 pitch, or make pads to solder to, and use both sides of the board (instead of through-hole).   I don't know what everyone is using these days, but an ATMEGA32U2 would be smaller and still give you all the connections you need - even better if you have what it takes to solder the 5mm QFN package vs the 9mm TQFP one.  I'm sure you can make something quite small if you design it yourself and make it specific to your requirements.  At that size, it won't cost much to make either.

[Tactile]

How thick is that plate? Have you considered sliding the controller sideways into a slot? A Teensy is about 18mm wide.

[cribbit]

Plate is 1cm thick.

There are a couple of things that stand in the way of making things smaller.  Placement of the USB port, reset switch (make this a set of pads you jump, instead of a switch), the size of the package of the controller, say TQFP vs QFN, and the size/spacing of your solder pads for your wiring.   The 2.54 pitch through-hole spacing on the teensy and the like just takes up... well... space... but if you're going to solder SMD bits anyway, maybe go with 1.27 pitch, or make pads to solder to, and use both sides of the board (instead of through-hole).   I don't know what everyone is using these days, but an ATMEGA32U2 would be smaller and still give you all the connections you need - even better if you have what it takes to solder the 5mm QFN package vs the 9mm TQFP one.  I'm sure you can make something quite small if you design it yourself and make it specific to your requirements.  At that size, it won't cost much to make either.

Thanks for the advice!

Placement of the USB port can be resolved by putting it in the little area next to the square which would leave the square for the chips. I should also be able to fit some pin holes behind the port.

It seems so obvious in retrospect to change the pin holes for smaller ones, that should make a custom PCB easily fit.

Sadly I've never soldered SMD before. Where would I even go about ordering these components? Gotta relearn how to design it as well, I messed around with Kicad previously but never got very far.

[devoi]

The smallest 32u4 board available (afaik) is the beetle (https://www.dfrobot.com/product-1075.html) - there's only 10 digital IO pins but you may be able to do something clever with charlieplexing. Someone on reddit made a 18x17 board using the 16 output pins that a pro micro has, so you may want to talk to them (https://www.reddit.com/r/MechanicalKeyboards/comments/6wj1ri)

[cribbit]

The smallest 32u4 board available (afaik) is the beetle (https://www.dfrobot.com/product-1075.html) - there's only 10 digital IO pins but you may be able to do something clever with charlieplexing. Someone on reddit made a 18x17 board using the 16 output pins that a pro micro has, so you may want to talk to them (https://www.reddit.com/r/MechanicalKeyboards/comments/6wj1ri)

Major ghosting issues sadly I looked into charlieplexing previously for another project.

[cribbit]

Someone pointed out https://www.crowdsupply.com/uduino/uduino I think that will work quite well.

[ErgoMacros]

That uduino is so cool!
20 IO ports, so 100 keys in a 10 x 10 matrix, max. Looks like twice what you need.

Sadly I've never soldered SMD before. Where would I even go about ordering these components? Gotta relearn how to design it as well, I messed around with Kicad previously but never got very far.

I'm new to SMD too. Got a practice board and components from Amazon https://www.amazon.com/gp/product/B00Y20JYTM/ and dove in. I'm no EE or professional assembly person, just a very occasional hobbyist. Started to do fairly well less than 10% of the way into the board.

Very doable. Oh, I did watch about 2 hours of SMD YouTube videos too.

Best

[pomk]

Buy one of these, after they become available:
https://deskthority.net/resources/image/36574

[cribbit]

Buy one of these, after they become available:
https://deskthority.net/resources/image/36574

That's quite cool! Unfortunately for this project it won't work well but I can see it being super useful for other similar projects.

https://deskthority.net/workshop-f7/keytee-controller-breakout-board-for-small-keyboards-t15586.html is also similar to that.

[pomk]

Buy one of these, after they become available:
https://deskthority.net/resources/image/36574

That's quite cool! Unfortunately for this project it won't work well but I can see it being super useful for other similar projects.

Why not? The usb signals are routed also to exposed pads, so you can solder a cable directly on board as well.

edit: or at least give the measurements that it would need to fit into, so we can assess the possibility of a custom controller.

[cribbit]

Buy one of these, after they become available:
https://deskthority.net/resources/image/36574

That's quite cool! Unfortunately for this project it won't work well but I can see it being super useful for other similar projects.

Why not? The usb signals are routed also to exposed pads, so you can solder a cable directly on board as well.

edit: or at least give the measurements that it would need to fit into, so we can assess the possibility of a custom controller.

It would cross between two keys, meaning I would have to dremel down that entire gap.

The dimensions of the area are 24mm x 19mm but I would like to leave 1-2mm at the edges.

I am likely going to use https://www.crowdsupply.com/uduino/uduino as it is by far the tiniest board I can find that has enough pins.

[0100010]

Wow - will have to take a closer look at that...

[regack]

I threw this together just for fun, it's 19.05mm x 19.05mm and apparently would cost $2.85 at OSHpark... but then you'd need all the supporting bits.  19 IO pads (#20 I used for an LED indicator) and 4 pads for the USB.  Uses 0603 caps & resistors.... now i'm tempted to order the stupid thing just for fun, but I have no use for it.

[0100010]

The more I look at that µduino // the more I like it...

[cribbit]

It's ridiculous that no one has managed to do it before. People have tried and done stupid designs, like the Arduino beetle or Pico.