I recently revisited the prototype I made for the Arduino and Rockwell 10941/10939 chipset project. Ever since I made that prototype I wanted to design a proper PCB for it. I finally came around doing just that.
Why
The prototype setup for testing the signals coming from the Gottlieb System 80B MPU board was pretty crude. Ever since I made the prototype I had the urge to design a proper PCB for it, and I finally came around doing that. Designing the PCB also was a nice way of improving my PCB design skills.
Schematic
The schematic for the PCB is pretty straight forward. The board is nothing more than an adapter for connecting the edge connector to a bunch of headers and test points. The most important connections made by the board are the eight data lines and two chip select lines that go straight to the Arduino Nano.
The only components aside from the headers and test points are two pull-down resistors, one for each chip select line and the LED and its resistor connected to the +5V supply from the edge connector.
Design
I designed the board with KiCad. KiCad comes with footprints for most common components. The only footprint I had to make myself was the footprint for the edge connector.
I made the footprint for the edge connector based on measurements of the actual edge connector on the MA644 display board. After making the footprint I printed the outline of the board, which included the outline of the edge connector, to verify it would fit the connector coming from the MPU board.
It turned out I had to make some slight tweaks to make the connector fit better. After doing so I finished the design of the rest of the board and sent out the design files to the PCB manufacturer.
Manufacturing
I had the boards made by JLCPCB. I chose to have this board made with a black solder mask with a gold plated finish. The reason I went with the gold plating is that the edge connector will have some mechanical wear and a gold finish is better suited for this wear than a tin finish.
Features
Because I designed a PCB specifically for this purpose, I had the chance to add some features which the prototype did not have.
Edge connector
The edge connector was the hardest part of this board to get right. Luckily, the edge connector fits perfectly on the board. I also added labels and numbers to each pin on the connector, based on the original schematics for the MA644 display board.
Arduino Nano
The Arduino Nano socket has an additional row of headers on each side to allow for connecting other stuff to the used Arduino board.
There are also two small prototyping areas next to the Arduino Nano. There was some empty space left there which I filled with these prototyping areas.
Signal line headers
The signals from both the DATA pins and the LD (chip select) pins are broken out to their own headers which each have an additional pin for GND and +5V. This allows for connecting the headers to a logic analyzer without the need for an Arduino Nano.
Test points
Each power line coming from the pinball machine has a test point to allow for testing the voltages with a multi meter while the board is connected.
Power LED
There is a power LED to indicate that there is power supplied on the +5V pin of the edge connector. It has a jumper to disable it.
There is a second jumper next to it for connecting the supplied +5V to the board’s +5V plane. This might be useful when not using an Arduino board.
Result
Conclusion
The original prototype was made specifically for testing and verifying the signal integrity of the signals coming in from the MPU. The board I designed based on that prototype can be used for a few other applications too.
Its main purpose is still testing the signal integrity, but it also allows for modding your pinball machine to support an alternative display or creating a test bed for Gottlieb System 80B MPU boards.