Pokémon Pinball but you can rumble whatever you want

Pokémon Pinball is a game for the Game Boy Color that was released in 1999. It's notable for coming in a cartridge format that Nintendo called the "Game Boy Rumble Pak," meaning it's a Game Boy cartridge with a vibrator motor built in.

Something I've wanted to do for a long time is make something like the Rez trance vibrator but for Pokémon Pinball, on a real Game Boy, and without altering/damaging an original cartridge. This required both a ROM hack and a custom link cable peripheral. The 666ames Made Quick Game Jam was just the motivation I needed to actually do it!

This isn't a very Game-Jammy submission, if you ask me, but it does keep with the Game Jam Tradition of being a bit slapdash and poorly documented (but, hopefully, in an endearing way??). If you are at all interested, please leave questions or comments! If any part of the project does not make sense, the fault is entirely mine; please let me know which parts interest you and which parts I can try to clarify.

Part 1: Putting the ROM on a cartridge

The ROM hack is available here as a patch in .ips format. Use a patching tool like Lunar IPS to apply the patch to the ROM Pokemon Pinball (U) [C][!].gb with hash sha1: 9402014d14969432142abfde728c6f1a10ee4dac. To play this ROM hack on an actual Game Boy, I got a cheap repro cart from AliExpress (it was sold as Pokémon Battle Factory and had a Charizard on the cover) and overwrote it using a GBxCart RW v1.4 Pro. I had never done this before; I had this blog post by JinGen Lim to guide me on what to buy.

Part 2: Sending data from cartridge to microcontroller

That one-millisecond pulse of data being sent over the link cable won't drive your vibrator directly. First it has to be read by a microcontroller of some variety (well, you could do it with analog parts....but that's a different project entirely).

The downloadable .ino files are badly-documented example projects for a "normal" Arduino or for an ATtiny85 running ATTinyCore. Each project listens for an 8 kHz clock signal from the Game Boy and one byte of data, which it then uses to do some type of motor control.

Part 3: Actuating a rumble device (or whatever) from the microcontroller

The microcontroller has received a byte from the cartridge, now what? It depends on the nature of the device you want to control. In the example Arduino sketch, no device is controlled, it just sends a message to the Serial Monitor with the details of the signal received. In the example ATtiny85 sketch, the microcontroller puts out a PWM signal to drive a high-side P-channel MOSFET switch. If I had a larger device to drive (like, say, a Hitachi Magic Wand), I'd need some different control circuitry. So, this part is still uncertain and open to suggestions!

You can maybe see in the video I made a custom PCB that the link cable plugs into. It's not very good, I think it would be a hindrance if I shared the design files here. If you want to make a PCB please talk to me directly, it is one of my favorite things to discuss <3