I got a hold of an old EM Stock Car pinball machine a few weeks ago with the hopes of repairing it, but my first attempt ended in failure. The machine had been sitting in a damp, moldy garage against a wall, under a leaky window for at least twenty years, and it was beyond repair. About a third of the inside was covered in mold, all the moving parts were stuck, all the metal was rusted, and the back glass was damaged beyond repair.
So instead I realized that this would be a good way to use an Arduino. I could just plug one into all the inputs and outputs of the machine and then program it to react in the same way all those complicated and broken electronics would have. I ordered an Arduino Mega, which has 54 I/O ports, and then got to work investigating how complicated it would be to interface it with the pinball machine.
Some quick testing revealed that all the moving parts of the pinball machine ran off 25V AC, which posed my first problem, as the Arduino runs off 5V DC. Asking about how to fix this online wasn't much help; the experts couldn't even agree on whether an AC coil would work with DC. Being the pragmatic and cautious individual that I am, I of course took the rational route, and hooked two old car batteries up (12V DC each x2=24V DC) to a solenoid to see if it would work. (It did). Of course, this still left the big problem, which is that even if the coils would work off DC, they still needed 25V.
The answer, of course, was to use a transistor, or a MOSFET to be precise (I still haven't figured out the difference), to switch the high power current with a low power current from the Arduino. Three burned out husks of transistors later, I'd figured out how they worked, and rigged up this insane hodgepodge of circuitry to control the eight solenoids in the machine.
After an arduous day soldering wires to all the components and hooking them up, I now have control of all the moving parts of the machine from my Arduino.
Tomorrow, I get to start working on wiring all the rollovers to the Arduino so it can begin actually scoring points
Posted Sunday, April 01, 2018
at 06:06 PM
Some ugly Spring Break artwork wouldn't do, so I spray-painted the cabinet black:
The same went for the head:
I've never understood pinball machines that couldn't think of a use for more buttons, so I put a second set in:
I picked up a sheet of 0.5" MDF at Home Depot, and lightly drew out my layout
I also used leftover scraps from cutting it to the right size to experiment with mounting components
Using a small router and an 1/8" bit, I found that, as long as you go slowly, it can produce workable light insert holes
Since I couldn't find any launchers, I made one myself by welding a scoop to a piece of 0.5" iron stock and attaching some plastic to the front to guide it
When you power the coil, it pulls the iron stock in, and the plastic guides it through
After two trips to the Allentown PinFest, I've managed to get together pretty much all the components I'll need for the build.
I got two boxes of assorted used parts for $20, and a ruined, half populated Spiderman playfield for $30, yielding an assortment of playfield parts:
I also bought a head from a mysterious 4 player EM for $20:
I really wasn't looking forward to the thought of trying to assemble a cabinet from scratch that would work with regular parts, but luckily I found this slightly beaten Spring Break cabinet for $15
(the legs were separate, another $20)
It even came with a working power supply, so I didn't need to worry about finding a 25-50V power supply. I was able to find a combination of taps that put out 28VDC after recification. Most non-EM pinball aficionados seem to think that 50V+ is the way to go, but honestly the flippers seem just as strong on my 25V games as my 50V.
I put in an order to Digikey for $70 (!) of electronics, including some high power MOSFETs for the solenoid drivers:
, some parts for making molex connectors,
, three CPU boards (basically cheaper, more powerful, lower level Arduinos),
...and a ton of stuff for audio output, including this surface mount op-amp, which turned out to be *really tiny*
I made some nice compact solenoid driver boards
Looking at schematics for actual machines they've got all kinds of weird stuff, however just a MOSFET, two resistors, and a line to the CPU were enough to fire the solenoids just fine. I wish I had some way to turn them off in case the CPU locks up while one is turned on, but I don't know what that would be, and as far as I can tell 'professional' machines don't do it either.