A couple people have wondered why I’m not just using the P-ROC solution instead of rolling my own. It is a very valid question and the design reasoning behind my boards may help some people decide what is best for them.
The original open pinball project design was to use a Xilinx Spartan 3A FPGA for doing all of the solenoid driving, lighting, and digital inputs. If you jump over to the P-ROC site, they are using the exact same FPGA. One benefit that they have is that they can use the BGA part. I can’t solder a BGA part at home, so I would need to send it out which is far too expensive. My other option would be to use the QFP part which increased the price and reduced the number of outputs significantly. (The 144 pin part is about $22 each in quantity 1 and it only gives you about 97 I/Os, or $22/97 = .22/I/O pin) Next I looked at the price of the small crappy processors in quantity. (Remember, I’m only going to build 10 pinball machines at a time, so price in low quantities is very important. Using the same chip in multiple locations gets my quantities up significantly) The design uses 24 solenoid drivers (3 driver boards), and 64 inputs (4 input boards). (I chose the MC9S08SE8 because it came in a 28 pin dip package which is really easy to dip solder. It gives you 20 usable I/Os per chip. So that’s 7 processors/machine or 70 processors at a time. Because of the price break, it is cheaper to buy 100 processors than 70, so 100 processors is $108. My price per input is $108/70 processor/16 I/Os = .10/I/O pin. This is about 1/2 the price of the Xilinx solution).
Last part of the solution is to use 74LV595 to run LED lighting. These are simple shift registers with a latch bit. I can run these at a lower voltage so I can get rid of the current limiting resistor on the LEDs. There are 8 of these per pinball and each chip is $.60 in quantity, so they are .075/output pin. My guess at my design is that I need 8 of these per pinball machine.
Some of the functionality that the P-ROC is using is not necessary in my case. The P-ROC supports a DMD display. When I looked at the price of a DMD display in low quantities , it was significantly more expensive than using a 22-inch monitor. Look at the Jersey Jack website. The reason that they went with an LCD display instead of a DMD display was not because it looked snazzier, but because it costs significantly less, and gives you more functionality. (By the way, I stated I would use a display before Jersey Jack announced they would use a display, but my reasoning was simply based on price.) A display/mini computer solution is currently less than $200 in quantity 1. The only downside is that you need a really good graphic artist to do all of your video clips. That is going to be a big pain to figure out how to pull all the video stuff together because I have no talent in that area.
By the way, displays are now so cheap, wouldn’t it be cool to embed a touchscreen in the playfield so that it could track the ball as it goes across the playfield? You could have graphics of jet trails following the ball, objects on the playfield that the pinball needs to hit, etc. This would be different than pin2k which is using a screen to project objects on the playfield, but still uses physical switches to register hits of these objects. Wouldn’t it be cool to have a pinball with flames following it? All of these ideas should be relatively easy to implement with a touchscreen below the playfield. The only problem is whether the touchscreen can stand up to the abuse.