MegaPi - Replacing the innards of a Megadrive 1


#1

I’ve embarked upon a rather unconventional journey to mod a Sega Mega Drive 1. The goal? Without damaging, changing or modifying any of the external appearance, or the internal plastic I’m challenging myself to completely replace the insides of the Mega Drive 1 with a Pi-powered equivalent.

It should be compatible with Mega Drive games, Mega Drive controllers, and should output an RF video signal. The front audio and volume control should work, so should the reset and power button. The more indistinguishable from a real Mega Drive 1, the better!

Here’s the unfortunate subject- a fully functional Mega Drive 1 ( I’ve tested it! ). Don’t worry, I’ll be placing the old innards to one side and preserving them.

And here’s what it looks like with the lid off:


Greenhouse Watering Controller, Pi Zero W, Automation pHAT
#2

Great idea. I’m doing something similar with an old PlayStation One (original, not the naff looking rounded version). In fact, I’ve just posted a thread on the support forum regarding powering LED’s etc. Will be happy to share the completed build once it’s done and dusted though!

How is the MegaPi project coming along then?

PS - I like the name - I had “coined” it for an idea myself, which was to house the RPi inside an old Megadrive game cartridge - in fact I even went as far as to create a custom label myself!

Take a look:

PPS - The idea I had involved two top layers of old Megadrive cartridges, so the label folded over them to create the look. I didn’t want to cut any unnecessary slots in the cartridge, so thought this might be a good idea!


#3

It’s actually come along quite well, but it’s been stalled for a week weeks because I’ve just not finished the PCB designs and pressed the “go” button on prototyping.

I’ll have to update this thread with pictures, but I’ve successfully cut the Retrode 1 PCB so that it fits into the right place inside the Megadrive. I also had to remove the USB port and solder a USB cable in its place, since the port was too big to fit next to the dust guard around the cartridge slot.

Everything inside is connected to a laser-cut-Perspex mounting plate, which slips in where the Megadrive mainboard used to sit, and fits like a glove ( due to several exhaustive measurement and paper prototype cycles ).

Ideally all the wires will be hidden underneath this plate.

RF Video Out is working, thanks to a hacked N64 RF converter. I removed the casing and port, then soldered it via wires onto the test points underneath the Pi so that the existing AV jack could still be used for the U-DIN connector on the back.

The controls on top will be the most difficult challenge, I’ve got a bodged on Flotilla Slider at the moment which works but feels rather naff. If I were doing a destructive build then I’d cut the relevant portion out of the original PCB, but I’m going to have to re-create it as best I can.


#4

Sounds exciting, and I personally am looking forward to seeing the results once you have completed the project!

So the idea will be to use existing game cartridges, but you’ll be able to use Megadrive, SNES, NES etc. cartridges using the Retrode?

What part is the RPi going to play in this?


#5

Here’s an image showing the mounting plate:

And then Pi and Retrode in place:

And the N64/Gamecube composite to RF modulator soldered right onto the AV output jack of the Pi. It works, honest!


#6

The fun you can have when you have the fab tools to hand hey! Looks good so far - looking forward to the completed project too. I hazard a guess that my attempt with a PlayStation (original not the slim) case and a Raspberry Pi 2 won’t look so professional inside!


#7

Any chance of the design file for this mounting plate, or shall I shut up ;)


#8

Haha, yes, I’ve been away for the last week and the design file is… somewhere! I’ll dig it up A.S.A.P!

Edit: Uploaded the original .ai file here: http://pi.gadgetoid.com/megapi/mountplate.ai


#9

Fantastic, don’t suppose you know of anywhere that will laser cut perspex for me? And what thickness/material did you use?


#10

Found someone, thanks again!


#11

This is awesome stuff. Is there any way you could post the pin description on the RF mod and the PI?


#12

The RF mod is laughably simple, actually, I just went to a used games shop in Manchester and grabbed a couple of Gamecube RF adaptors. These are little plastic boxes that plug into the Gamecube composite out port, and just convert it to RF.

Once all the plastic casing is ripped off, and the Gamecube-specific connector removed you’re left with a pretty simple inverter that has connections for Left/Right audio and Video, plus power and ground.

If I recall correctly, I used mostly trial and error, plus a bit of “Well this trace looks like power, and this one is obviously ground” to figure out how to wire it up.

I’ll see if I can grab some more photos and produce a slightly more useful guide. It should be possible to do the same mod with pretty much any off-the-shelf Composite to RF converter.


#13

That woudl be awesome. I have some at home, N64 RF mods and they look identical or are the same by a differnt name.

My question is which wires go where, e.g. audio 1,2 to PI pin XXXXX : GND to PI GND, etc,

As the photo is upside down, its hard to see which pin the RF wires come from and which exact pin they go onto the PI + the PI version I have is older so the PIN layout is different.


#14

N64-rf-mod


#15

I can’t remember which Pi I used here, but the wires are soldered onto a number of test pads and pins.

I used conventional colours (mostly) for the wiring, so your intuition on what the wires are is correct.

Grey/White for L/R audio (not sure if they’re in that order), Yellow for Video, and Red/Brown for +5v and GND if I recall correctly.

It looks like a B+, so here’s the list of test pads: https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=89522

And here’s a photo of the underside layout for reference: https://upload.wikimedia.org/wikipedia/commons/4/48/Raspberry_Pi_B%2B_bottom.jpg

So, let’s try to figure this out:

Red     |  +5v    |  PP27 VBUS (USB +5V Power)
Brown   |  GND    |  Physical Pin 39 (ground)
White   | Audio L |  PP25 AUDIO_L
Grey    | Audio R |  PP26 AUDIO_R
Yellow  | Video   |  PP24 COMPVID

This will very highly from Pi to Pi and you might want to use a TRRS (or is it TRRRS?) video/audio jack into the onboard connector, versus soldering on. I wanted my wiring to be hidden under the mounting plate, so I went this rather crazy route.


#16

Tried but unlucky. I have video, GND and 5V hooked to the rapsberry but no picture. It works with a standard RF od but not this one. Would the channel and settings be different to tune to?


#17

First of all thanks for sharing the mounting plate file. I’m making a similar project and the mounting plate template will be very usefull.

In early 2017, Tectoy (the same distributor of Mega Drive / Genesis in the 80s / 90s here in Brazil) launched this console again.

As they could not produce the same original internal components they used the RedKid chip (the same as the AtGames uses) and to lower the cost of production they used RCA video output instead of HDMI.

So here in Brazil we have a Mega Drive that accepts game cartridges and roms (through a micro SD-card) but that does’t have HDMI connection for new TVs and that changes the sound of some games like the consoles of AtGames.

That’s why I decided to make my own Mega Drive using a RPi 3 inside a Mega Drive carcass.

At first the initial goal is to just emulate the roms but after reaching that goal I will try to make a way for the system to run games of the cartridges.