N64/Snes/Nes controller to gamecube/Wii conversion project

Here is a picture of the schematic. Click for bigger version:

Nes/Snes version:	N64 version:

Comments and explainations:
The microcontroller is powered with 5 volts for three reasons:

Snes and Nes controllers work at 5 volts. This means that it's better to use 5 volts for a logic 1 when driving the controller's CLock and Latch pins. (As I dont have the official controller specifications, I cannot know for sure what is the voltage threshold for a logic 1.
The data signal from the controller is at 5 volts when high. To prevent exposing the microcontroller input to voltages higher than it's own, it would have been necessary to use a voltage divider which would have required two additional resistors.
If I had powered the MCU with only 3.3 volts, I would have had to use an ATmega8L which cannot run at clock rates above 8 mhz.

On the gamecube side, the data signal is held at 3.43 volts via a pullup resistor inside the Gamecube. When someone (gamecube or controller) wishes to set the signal to 0, it just has to pull the signal to ground. Otherwise, it just leave-it as-is. I acheive this by playing with the Atmega8 pin direction. To send a 0, I configure it as output-low. Otherwise, I configure it as input-no_pullup. Activating the internal pullup or sending a 1 in output mode must not be done since this would put 5 volts on the data line. Who knows if this could damage the console port? (In fact, I have a cheap wireless controller which drives the bus with 5 volts! Nothing seems to have been damaged though...)

The N64 version uses the same technique to control the controller's data line. The only difference is that we have to provide the 3.43 volts pullup resistor. (From the controller's point of view, we're the console!)

FAQ:
Q: Why did'nt you use the Wiimote accessory connector instead of doing a Gamecube adapter?
A: I considered it, but I decided that using the Gamecube ports was better. Here are a few reasons:

NES and SNES controllers use 5 volts. If I remember correctly, there is no 5 volts in the Wiimote connector. This means that I would need to build a step-up switching voltage regulator. Higher cost, Higher complexity.
NES and SNES controllers were designed to be wired controllers. This means that they probably did not have low power consumption in mind when the designed it. But I did not take the time to very that because of point #1
The Connector is proprietary. Gamecube connectors are too, but they can be easily obtained from extension cables, which are cheap and easy to find. At the time, I failed to find wiimote extension cables
NES/SNES (and other consoles) emulators on Wii are (or were, I have not checked recently) in fact Gamecube based. Since Gamecube games only support Gamecube accessory, implementing the adapter via the Wiimote would be useless.
I'm not a big fan of wireless things. Besides, the NES/SNES controller cables never bothered me.

Reference

Description

Comments

Digikey part #

10uf capacitor

1uf is enough too. And smaller value capacitors are slimmer.

490-1835-1-ND

C2,C3

18pf capacitor

Change as appropriate for crystal.

311-1102-1-ND

16mhz crystal

Suggested part number is for a surface mount crystal. Can be easily soldered on the thru-hole footprint.

644-1037-1-ND

R3,R5,R6

0 ohms resistor

You can do a solder bridge instead.

N/A

Atmega8 microcontroller

It is important that you use the family supporting a 16 mhz speed. The Atmega8L-* family does not go above 8mhz.

ATMEGA8-16AU-ND

Type de manettes

Version

Fichier

Commentaires

Nes/Snes

1.1

snes2wii-1.1.hex

Changes in this version:

NES mode can be forced on by holding the Start button at power-up. Without this, in my opinion, NES games are almost unplayable with an SNES controller.
Implemented button combinations which can affect how unaccessible Gamecube buttons and sticks are reported. eg: Sending L+R pressed with a NES controller, and sending "CStick towards the right". Mostly useful to summon some emulator's menu while playing.
Implemented new Gamecube commands for better compatibility, eg: GCLinux.

Nes and Snes

1.0

snes2wii-1.0.hex

This was the first version. Nes or Snes mode selected with jumper.

Nintendo 64

1.4

n64_to_wii-1.4.hex

New in this version:

Added 4 new button mappings, accessible by holding a C button for each mapping. These are reported to be useful for Super Smash bros Melee and Brawl.
Created a single page PDF documenting the supported mappings

Nintendo 64

1.3

n64_to_wii-1.3.hex

New in this version:

It is now possible to disable the feature where the L and Z buttons are swapped by holding the 'L' button down when plugging the adapter in the console.
If the R button is held down when plugging the adapter into the console, the N64 C-left and C-right buttons are mapped to the Gamecube Y and X buttons. This makes it possible to play the virtual console game Sin and Punishment.
The joystick sensitivity can be increased by holding the Dpad right button when plugging the adapter into the console.
The joystick sensitivity can be decreased by holding the Dpad left button when plugging the adapter into the console.

Nintendo 64

1.2

n64_to_wii-1.2.hex

Version 1.1 for N64 had a reliability bug which caused some controllers to randomly reset and recalibrate during play. This is fixed in version 1.2. It is recommended that you upgrade even if version 1.1 is working for you.