Ok. Enough of this soldering and coding. Lets put the machine back together and see what happens. At this point we have quite a lot of confidence that our little proof of concept hookup will work. What's the worst thing that could happen? Ok, electrocution, but besides that?
We took our CPU board, prototype breadboard, home brew cables and a Laptop over to the Pinball machine and started putting it all together. If all goes well, we will turn on the machine, push the credits button and a little LED on the breadboard will light up. With a few shrugs of shoulders and very little fanfare, the following took place.
First we hooked up the cable to the protoboard and the CPU board. After carefully checking and double checking the connections here is the cable hooked to the CPU board.
Then we carefully refit the CPU board into the pinball machine. Now, we really didn't think a few things out here. For example..how long the cable needs to be. A little creative grabbing of a box laying nearby and viola...ready to run.
We elected to leave the speakers and the plasma display disconnected. Mostly because random data flowing to the speakers could be really unpleasant. I've heard amplified random signals blaring from a speaker. Not fun. And why destroy a perfectly good plasma display? Those things are expensive. It shouldn't come into play at all for this test. Besides, we'll have ample opportunity to mess it up later on.
I should now reiterate that we are playing with high voltage here. We don't intend to go anywhere near it, but we could very well have screwed up. So disclaimer time again.
So, not much left but to see what happens. We plugged the machine back in and turned it on. It didn't blow up. No smoke, no noise. In fact everything looked downright correct. Nothing happened. Only the indicator LEDs on the CPU board lit. In addition, our "test lamp" LED started to flicker. Hmm. Getting some kind of signal. Looking kinda random, but clearly getting something from the pinball circuits. Not however the resounding success we were looking for.
After staring at things for a bit, we started checking some values with our handy multimeter. We were clearly getting a +5V read at the D7 data line input, which flickered as the SWLO bank was disabled and enabled. No matter of pushing any of the buttons made any difference to the value getting to our board. When measured at the input connector from the switch itself (on the upper edge of the CPU board) we clearly saw that the switch value is +5V in open position and gets pulled to ~0V when pressed.
Ok, not successful. We decided to leave the CPU board in the machine, and pulled our cables and protoboard back to the worktable. We had little faith that the way we hooked up our little LED test light was correct. In fact, we were pretty sure we needed to find a better way to test things, particularly as we move forward with more complicated tasks.
That put and end to our workday, sending us off to ponder code and connections. A bit of rest would lead us to a few keen insights. I'll save that for next time.