Trinket Pro as controller

[geauxtig3rs]

Long time lurker, first time poster.

Looking at doing a custom build, all on my own.  and had one question that I think I know the answer to, but I needed some guidance from some more experienced members.

I'm working on a 40% ortho (think planck).  I've got 12 columns, 4 rows, 2 foot switches.

I'm looking at using a trinket pro instead of a teensy to save a little bit of size.  It's an ATMEGA328 with 18GPIOs.  I've seen a couple tutorials for using it as an HID, very small scale, but it seems similar to doing the same thing with a Teensy.

Any reason this won't work?

[neverused]

The ATMEGA328 does not support usb natively, so you would have to use v-usb, but beyond that it may work.

It should be cheap, you can always try it out. I think hasu's firmware supports that MCU.

[technomancy]

I'm looking at using a trinket pro instead of a teensy to save a little bit of size.  It's an ATMEGA328 with 18GPIOs.  I've seen a couple tutorials for using it as an HID, very small scale, but it seems similar to doing the same thing with a Teensy.

You can get it to work if you write custom firmware, but it'll be more complicated not having native USB.

I would recommend using the A-Star micro instead: http://www.pololu.com/product/3101

It's smaller than the Teensy, uses micro USB, and has the ATMega32u4, which is the same chip as the Teensy. Only the bootloader and pinout are different.

[twiddle]

You also have the option to go with a compatible clone of a Pro Micro or a Nano. Adafruit stuff can be expensive to get hold of depending on where you are, so you might be able to source the clones cheaper than the trinket - and they have native usb rather than requiring V-USB to bitbang the protocol.

If you still want to go with a ATMEGA328-based chip and use TMK or V-USB, you could also look at Pro Mini - http://arduino.cc/en/Main/ArduinoBoardProMini
Clones sell for under $5 (I've used Deek-Robot with some success before, note the dash in the name), and you would just need to solder a USB socket onto it (they are cheaper in part because of the lack of onboard USB connector). You can use the analog pins as digital GPIOs, so its got 22 GPIO altogether.