HP HIL to PS/2 may work.

[486]

If you, and may I mention not many have, tried vintage HP keyboards, you find them one of the best linear keyboards out there. The feel is so different to anything else. It has a semi clicky metal prong under a pcb mounted tactile switch which give a strange but nice feel. Anyways, I have 3 of these babies and they are awesome but one thing troubles me. HP had a stupid idea of using a non standard connector with the keyboard (HP HIL, a 4 PIN SDL variant of IBM Model M). true there are adapters's but non of these really suit me as the cost of them is way to high. e.g. http://www.ebay.com.au/itm/HP-Agilent-Test-Equipment-Workstation-KEYBOARD-ADAPTER-MODULE-/380425460011?pt=LH_DefaultDomain_0&hash=item58931fd92b
 The cables are hard to find as well but recently on EBay I had a look for cables and found something that may give hope for the kbdbabel project on these keybords.
This auction http://www.ebay.com.au/itm/HP-Agilent-Test-Equipment-Workstation-KEYBOARD-ADAPTER-MODULE-/380425460011?pt=LH_DefaultDomain_0&hash=item58931fd92b has 5 HIL cables, one very interesting one though. In the auction is a HIL to DIN cable. This verifies that the keyboard must have some kind of AT protocol but I suspect only with normal AT keys.  However I will attempt to figure this out and hope that I may be able to mod this wonderful keyboard. Futher research of this HIL to DIN cable model no: 5081-2249 reveals that the HP HIL keyboards were used with HP's VECTRA PC compatible lines. One example of a HIL keyboard bundled with a AT computer is the Vectra QS/16. I believe that to be sufficient enough to support the theory that HIL keyboards support the AT protocol. Next thing is finding out which pin in SDL connector is which in the AT connector. I know what is VCC and what is ground thanks to the fellas at kbdbabel but alas not clock or data. I'd guess i'd better have an educated guess.
I give you guys an update if anything comes about.

[mich]

I doubt that. I own a HIL mouse and its label clearly states that it runs at 12V, while AT keyboards run at 5V.

[486]

True, I figured that out too, but maybe with a step up converter. I have to investigate futher but maybe it has a jumper which can be changed to enable usage at  5v