HP-41 Unknown Interface

[Juergen Keller]

Somebody pointed me to this HP-41 with an unusual custom interface, see pictures. Has anybody seen such an interface before? Or does anybody even know what it is for? Any hints and suggestions welcome!

[Mark Hardman]

I looks like a cereal port used to dispense the barley for your lager unit. <Ducks>

[Walter B]

:-D Oh yes, such ports are really a big help for mankind. What a progress along the lines of consumer interest!

[Randy]

Based upon the position of the wires that I can see connected, the interface is a simple extension of the keyboard row and column matrix, allowing external switches to input data into the 41.

[Andrés C. Rodríguez (Argentina)]

Just guessing, it may be a "paralell keyboard matrix" interface, in which external switches simulate keypresses. A 3x3 matrix, allowing (for instance) for digits 1 to 9 (but not 0) can be done with six wires, as shown.

If someone wanted to export the HP41 bus signals (clocks 1 and 2, Flag Input, Data, ISA) it would had make sense to pick them at one of the backplane ports

Again, this is just a quick guess.

[Howard Owen]

There appear to be three more wires, terminating somewhere on the reverse side of the circuit board. It's nine pins, built inside what looks like an HP/IL female connector.

[Andrés C. Rodríguez (Argentina)]

With three more wires a 5x4 matrix is possible, allowing for numeric data, decimal point, R/S and some more...

[Ángel Martin]

Wow, that's elaborate hacking - wonder if it's part of a data input mechanism different from the original keyboard - maybe an industrial bar-code reader?. I have no recollection of such being published anywhere, but yet, the 41 series was such a versatile platform - and this proves it again.

Edited: 28 Aug 2011, 2:59 a.m.