Looking for a USB keyboard encoder to fit inside a Saturn pad

[randombs]

Hi all,

I put RetroArch on my iPad and it works great with my Dual Shock 3 but that pad is no good for retro stuff.

Also, I'm heading to London soon and have been missing things like soldering and modding so I've got a crazy idea:

iOS doesn't have a HID gamepad driver but it does support HID keyboards so I want to put a USB keyboard encoder inside a Saturn pad and use it with my iPad.

I'm going to take the USB circuit and keyboard matrix from a faulty keyboard and see if RetroArch lets me map keys. If it does then I'm going to look into an Arduino-style USB chip that could fit inside the Saturn controller's casing. Or maybe my Megadrive 6-button pad. I think I still have that somewhere...

As for USB encoders/emulators, I've come across these so far:

Tinyduino
Digispark - very small and cheap but not enough input pins for a Saturn pad. I guess I could make a keyboard-style matrix so I can use all the buttons. That would be fun! Problem is it has the USB port connector on it.
Digispark Pro - more pins so no need for a matrix
Teensy - looks good but quite expensive

My question:

Is anyone using an Arduino/ATmel-kinda device as a keyboard encoder(e.g. for an arcade cabinet)?

Thanks!

[speedlolita]

Was gonna suggest a Teensy but...

https://www.pjrc.com/teensy/

This doesn't seem too expensive to me?

[randombs]

It'd be cool if you could just reprogram the chip already in a USB pad!

Maybe Digispark is the way to go, and I could just solder the wires from the USB cable to its USB connector. Micro USB would be too weak I think.

I'd love to attach the iPad to my DC stick to turn it into a mini arcade machine

Speaking of which, the dual strike in that does keyboard emulation!