Vectrex controller project help

cheeko · April 13

This analogue stick popped up on ebay cheap so I grabbed it for a few quid. I was thinking I could maybe make a controller for my Vectrex so I have a spare / preserve my original one.

I don’t have much electronics experience, I’ve built a usb arcade stick for my PC but those are really just plug and play kits. If I’m honest I just bought this because I haven’t seen any other joysticks that seem to operate in the way the proper vectrex ones do I would want to maintain the authentic analogue approach.

Here’s the stick, my question is, can I use this for a controller build, and if so, can you recommend how to go about it? Thanks!

It has a 5k potentiometer on it, not sure what that is but maybe needs replacing?

Edited April 13 by cheeko

gtoal · April 15

Two points:

1) 5K pot vs 10K pot: not a big problem. You can feed the two sides of each pot from a couple of voltage dividers, and build the voltage dividers using two of the small cheap trimpots rather than with fixed resistors, so that you can just tweak them to set the scale and to center the joystick accurately rather than have to work it out mathematically. You're going to want the trimpots anyway just to ensure accurate centering of the joystick at 0,0 so might as well also use them for the voltage dividers on the inputs to your joystick module. (Sorry, I don't have a specific diagram to hand, but basically its the same as the area at the top right of the diagram below, except that instead of using that digipot, you just use the joystick module (with PB0/PW0/PA0 being replaced by the joystick module's X pot, and PB1/PW1/PA1 being replaced by the joystick module's Y pot. All the other connections to that chip in the diagram are irrelevant when using a joystick module rather than a digipot) So 4 trimpots plus your joystick module are all you need. Easy to breadboard as a test. Just make sure the trimpots are roughly in their center before you power it up so that you don't short +5 or -5 to GND. (I've done that on my Vectrex and it survived but I wasn't at all happy about it and would prefer to avoid the risk.)

Ignore the button part of that diagram (which is only relevant to the USB to Vectrex converter that I took the diagram from). For a home-made controller you just connect the button wires through your button switches directly to the Vectrex ground wire. You should probably should put a resistor in the path between each button and ground but it really isn't necessary. It's cheap & hacky but it works.

2) Since you have a USB joystick already - you might be able to build one of these https://gtoal.com/vectrex/joystick/USB-to-Vectrex.html on a breadboard and just use your USB joystick? (We're also working on turning that into a PCB some time later this year.) Downside: it needs a Pi and some programming. Easy stuff if you're a programmer at all. Not an option if you're not a programmer though. The USB converter is basically the same circuit as what you need for your 5K joystick module except that the joystick is replaced by a single digipot chip - and a Pi to drive it.

Graham

PS The Vectrex test rom will help but I wrote this simpler joystick test code that you might find easier to use: https://gtoal.com/vectrex/joystick/AnaJoyTest.bin

Edited April 15 by gtoal
Added comment about the buttons.