Worked out the matrix, works fine. A lot of games don't use the 16 D-pad directions on the Intellivision anyway, and those that do are perfectly playable with four directions. I played Tron Deadly Discs for some time yesterday absolutely fine - in fact, seemed to have if anything more control on the character - the Intellivision controller was a bit "hit and miss" on accuracy at the best of times anyway. Further evidence, if needed, that 4 direction for the D-pad is fine is the "Intellivision Lives" compilations on the PS1 and PS2 as well as the rather poorly ported plug'n'plays for the Intellivision. Here's the product of several hours work and testing - all works fine. Using tact switches is so much better than the membrane ones, and, the tact switch matrix I built (10mm tacts) is the same size as the original mebrane set, so it would be quite simple to make a new controller with a better keypad and d-pad than the original Intellivision one, and still use the original game overlays! (I'm not making a replicate controller for my project, however this diagram would be useful if you wanted to make one). (corrected previous pic):
BTW - if anyone would be interested in commissioning me to make a replacement controller for the Intellivision, based on the above, using the original d-pad and replacing the stock keypad with tacts, etc; PM me. I can use the original controller although of course it will be thicker in the middle section than the original (the keypad section). I think £50 per controller including labour and parts is a very fair price, you provide a controller (I only have one spare one), i'll do the rest. Please PM me if you are interested, and we can discuss. Postage - UK £3, rest of world £10 incuding tracking. Payment in UK British Pounds, PayPal. First commission I would do i'd make the item first before charging, proof of concept, follow on commissions payment up front. PM me if you are interested.
I remember in the early '80's when I used to play the Intellivision with my father - after an hour or two of games, his finger got really quite black from pressing the controller pad so much. Memories, ahh!