Hey folks, some updates for you.
First, the device has a name! I've taken to calling it Eemix. It was going to be called "EMX" for "Electro-Mechanical eXtender," but that sounded kinda late-90's and wanky, like you were gonna have an X-treme X-pression X-perience or something, but "Eemix" is fun to say. Try it! Eeeeeeeeemix! Yay!
Second, Eemix is now on location testing in my 1972 Williams Super Star at DaBuzi's restaurant in Finleyville, PA, where you will find what I'm quite confident are the absolute best meatball sandwiches in the whole wide world ever! Response from the public who've played the machine has been very encouraging - high scores are addictive! Old, cheap machines can make money on location again!
Third, don't rush out there today because as I type this, it's broken! Out in the wild, on a location test where it's subjected to the chaos and randomness of the general public, Eemix lasted five whole days before needing me to go out and fiddle with it. Hell, for a prototype thing that no-one's ever tried before, that's actually pretty encouraging! I was expecting it to break down MUCH faster than that. I'm gonna write a better service/debug menu, grab my toolkit and head out there this evening.
Fourth, inspired by this thread (http://pinside.com/pinball/forum/topic/please-help-us-buy-a-pinball-for-the-disabled), I'mma tell you how Eemix's flipper control boards work. Here's a picture!
Note that none of this is to scale - I originally designed my schematic on graph paper, this is just a wee ten-minute Potatoshop mockup.
The big chunky thing at the top is the solid-state relay - one of these little fellows: https://www.sparkfun.com/products/10636
The chunk at the left is just a set of screw terminals, one of these to be precise: http://www.radioshack.com/product/index.jsp?productId=2102861
The big long bars are resistors - Eemix works entirely on through-hole technology, so that the average pinball owner can do any necessary repairs with a standard soldering iron, so they're fairly large as resistors go.
The squares with holes on them are my attempt at portraying headers like these: http://www.digikey.com/catalog/en/partgroup/0-100-2-54mm-pitch-connector-headers/24994 Those aren't the exact ones I used, I got a big bag off eBay, but a header's pretty much a header.
Here are the connections!
1. AC power - the wire that you desoldered from the flipper button switch.
2. AC power - the other wire that you desoldered from the flipper button switch. These get switched by the solid-state relay, now - and yes, removing that big old switch from the high-voltage side of the circuit does make the flippers a little bit more lively. Yay!
3. Connect to one side of the flipper switch.
4. (optional) Connect to one side of the auxilliary flipper switch (a 3.5mm socket, mounted underneath the machine).
5. Connect to the other side of the flipper switch.
6. (optional) Connect to the other side of the auxilliary flipper switch.
7. 5vDC. This would be supplied by Eemix's power supply - if you're using the flipper control boards without Eemix, you'll have to figure out a 5vDC source. If you like, you can get 5vDC from your 6vAC lighting circuit - this excellent post will help! http://pinside.com/pinball/forum/topic/open-source-freeish-pinball-electronics-kit-gi-buddy
8. (optional) 5vDC. Why are there two 5vDC headers? Because you'll need two of these boards! The other 5vDC header is so you can daisy-chain one board to another.
10. More ground, same reason we have two 5vDC headers.
11. This wire goes to Eemix, to tell it when you've pressed a flipper. If you just want the pinball-with-foot-pedals-or-whatever features, but don't care about high-score management or other Eemix functions, you can omit this (and the 100 ohm resistor) from the circuit.
So, to those who want it, what happens now?
Well, now it's going to keep breaking down or getting confused, and I'm going to keep going out and fixing it and doing software and hardware revisions until I have something that will keep running, flawlessly, for a few weeks at a time. This is a device intended for operators, designed to get classic pinball machines back out on location and earning money, so we're going to keep gathering data on all the things that can go wrong with it in an on-site context, and fix those things as they come up, until there's nothing left to fix. THEN, we'll start on making a production version.
In the meantime, I'm getting quite excited.