Electronic – arduino – Is it possible to use a non-Leonardo board to act as a keyboard or other device

I keep one FTDI cable around that I've terminated with breadboard pins for quickly connecting to, well, a breadboard! so I don't have a cable always hanging off my prototypes. I haven't bothered to implement auto-reset; I just use a reset button on the board. The timing that almost always works for me (in Eclipse) is to hold the reset button and release it just as I click Eclipse's download button. (Maybe someday I'll make a tiny PC boards to arrange all four pins into a pseudo BB-plug....)

This cable came with NerdKit AVR kit that was 5v based. So are my BB designs, currently. The FTDI head is on the USB-A male end; I just measured the BB end at 5.09v with no load (except, obviously, the meter). I think you only need to provide the appropriate regulator - 3.3v or 5v - as long as the input to it is higher than that (within reason). I power BB's with a 9v battery when I'm not using the cable.

I got the PJRC lib working through a stroke of luck -- I don't understand why this works. In the example sketch I use these definitions:

const int DataPin = 9;
const int IRQpin =  3;

But when I actually make the physical connections, I have to put the IRQpin (aka CLK) on pin 2 of the Leonardo. (DATA stays on pin 9 as expected based on the software definitions.) This software setup and the seemingly-wrong connection is letting me use the library as expected.

When I do move the CLK wire from the keyboard over to pin 3 I get the delayed and incorrect measurements mentioned in the question.

So I'm pretty confused as to why this mismatch in software and wiring works, but I'll keep searching..

Edit: Got things working properly. The Leonardo was not supported in the 2.3 version of the PJRC lib. I added some of the missing interrupt definitions in my fork.

Edit 2: Paul of PJRC told me that Leonardo support is now available in the PS2Keyboard lib he hosts.