Gameboy480p
The Gameboy480p is a small modification board for the classic Gameboy (a.k.a. DMG) that upgrades the headphone jack to also output a video signal alongside the audio.
The stereo output port is replaced by a socket of the same size but with one more connection (a TRRS jack instead of the TRS). The pinout is the same as for the A/V port on a Raspberry Pi. Unfortunately, many other devices also use a TRRS jack and their pinouts vary pretty unpredictably. Cables and adapters are available with sometimes no or wrong documentation, so be extra careful on what to buy. A wrong cable will not do any damage, but will just not work.
| contact | signal |
|---|---|
| tip | audio left |
| ring 1 | audio right |
| ring 2 | ground |
| sleeve | video |
The mod creates a 480p signal with 60Hz (approx.) that can be directly fed into any TV with a component video input. Connect it to the Y input which is the only one necessary for a black&white image. With many TVs it is necessary to also connect something to the Pb input to switch to the YPbPr mode. In this case you can use some spare RCA cable for this purpose.
Upscalers like the OSSC or Retrotink will handle the 480p signal just fine. As you manually chose the inputs, nothing needs to be connected to Pb.
My reason for using 480p and not 240p is that the Gameboy's vertical resolution is 144 lines which would look very small on a 240p display. By trippling the lines to 432 this now fits reasonable well on a 480p display and by some coincidence the pixels are nearly square when generated with a rate of 8.192 MHz.
To allow using the Gameboy as usual, the mod detects what is plugged into the A/V port and adjusts operation accordingly.
| mode | audio | video | detected by |
|---|---|---|---|
| no cable | internal speaker | disabled | video is not terminated |
| headphones | on output port | disabled | short between video and ground |
| A/V cable | on output port | active | 75 ohm termination on video |
This auto-detection should work for most cases. One exception could be a head-set with a microphone on the "sleeve" contact. This could be miss-detected as having no cable connected and audio will come from the internal speakers.
When the Gameboy is powered from batteries, power consumption is an important issue. These are my measurements of power draw directly from the batteries.
| configuration | power draw without any cartridge |
|---|---|
| original, no mod installed | 40 mA |
| no display detected | 47 mA |
| display active | 63 mA |
A game cartridge will increase the power consumption, but this will depend on the type of cartridge. My flash-based univeral cartridge already draws about 60 mA by itself.
The battery live will not be dramatically reduced by the mere presence of the mod when not actually using the video output. For longer game sessions using the video output on an external display, you should consider using a power supply, as you are already stationary anyway.
The mod board comes with 2 3-wire ribbon cables that need to be soldered to the board in a preparatory step. Solder from the bottom side as show in the picture.
To open the Gameboy, you will probaby need a specific screwdriver that was invented by Nintendo to prevent children from destroying their device. This looks similar to a regular philips screwdriver, but it has a 3-way blade. As far as I know, this can be sourced from various places, but I don't know any details.
After opening the Gameboy (there are also screws inside the battery compartement) you don't need to detach the top and bottom parts. You can just flip it open a little to access everything you need. I prefer to not disconnect the flat cable because I am afraid that the contacts are brittle after this time.
Then unscrew the audio connector board and desolder the 4 cables.
Put the mod board in the place of the original audio board. Be careful to not lose the mounting bracket in the process. Solder the 4 wires that were attached to he original board now to the mod board in the exact same positions. Do not yet screw the board to the case, you will still need to access the timmer potentiometer later.
