Zision Interactive

I realized that the top lanes still did nothing outside of the skillshot, so I decided to add a quick rule that one lane would give you more magna-pulses, but this reminded me that I still didn't have any ability to sense the flippers being pressed. I've been making do so far with using the secondary buttons for stuff like navigating menus, but you can't really use those during gameplay, and I want to add a status report soon since I'm getting to the point where the screen is getting filled up with information.

Since I'm using directly controlled flippers with high voltage contacts, this isn't as simple as it would be with software controlled flippers. I don't want to use switches on the flipper mechs like early games did since that seems to have some lag sometimes, and I can't add switches to the buttons since they're already double stacked for staging, so I'll need to do it electronically. Looking at other games, system 11, WPC, and gottlieb system 3 use opto-isolators to sense the HV signal going to the flipper, but I didn't have any on hand and have never used those before, so I tried to come up with a simpler solution.

My thought was, since my flippers are grounded by the cab switches, I should be able to just hook some 3V circuitry in parallel, since ground is the same for both. I put a diode between the chip and the cab switch to prevent the high voltage from going backward, and used a 74367 tristate buffer chip, so I could hook the switch matrix column to the enable to simulate a physical switch. A quick test with a breadboard hooked up to the switch seemed to work, so I assembled this one off board
Optimally this would have been part of my MPU board, but I wasn't sure what the circuit would look like at the time, so I left it off. Once it's battle tested I'll probably design a new MPU with the added stuff but for now this'll have to do.

Wired it up and ran into an issue... hitting either flipper button registered both sides. of course, not something I ran into when testing just one side with the breadboard. The signal seems to be traveling backwards into the playfield, through one coil to the HV line, then back through the other coil. I ended up just putting some beefy diodes in line between the flipper coils and the contacts to prevent that.

Also had an issue where the right flipper button (row 1, column 8 ) was also registering as the switch in row 1, column 1. Left button (row 7) was fine. Eventually concluded this was just due to the order I scan the matrix (row 1->8 for each column 1->8 ). I must be scanning it faster than the circuit through the chip can react, so it's still reading as closed for the next column (1 is after 8 ), but corrects itself before it gets to the other rows. Added a tiny delay after finishing the last column to account for that.