Wireless controller adapter for Commodore

 

It's August 2024.  I've just bought a new (to me) Vic-20 for US$50 to replace my childhood one.  I already have the PenUltimate Vic-20 Cartridge with a ton of games.  I also bought a Hyperkin Trooper joystick.  But I want to game wirelessly!

I've already had great success with a BlueRetro Nintendo GameCube controllers wireless adapter with my original Wii game console.  I purchased it on ebay for a good price and it worked great.

But I wanted to go back further to replacing an Atari joystick on my Commodore Vic-20 that has a DB-9 connector.  Searching the Internet, it looks like BlueRetro internally supports Atari 7800 with a 2-player mode, and there is a single player version available for sale on Amazon for about $25.  Also the ESP 32 firmware source code is available as open source.

Having experience developing with ESP32, and a plethora of electronic parts already at my disposal, I did what any enterprising consumer would do -- I purchased additional parts from AliExpress.  I mean, you can't have enough electronic parts, can you?  Okay, I could've done it completely from scratch but my time is valuable, I have only so much energy at the end of the day, and cheating my way to success is legal here.   So we're doing it halfway.

First I bought the BlueRetro Core.  It provides the base functionality with a DB-25 connector for all its pins.  It is designed to allow connector adapters to be wired to various console systems.  It is a very creative and functional design.  And there are adapters available for many of the common systems.  But I didn't have any luck finding Atari connectors.

But no problem!  I can build my own!  So I found a DIY screw terminal DB25 male connector with the correct optional mating screws, and the counterpart DB9 female connector with screw terminals.  The only trick left is to wire it up.

Steps

1. Connect BlueRetro Core to USB power adapter (don't require direct connection to computer)
2. Download latest firmware ZIP via link provided on BlueRetro support site
3. Unzip, and look for the parallel 2P firmware (1P should work fine too, skip the 3V3 versions.
4. Follow flashing firmware instructions from BlueRetro support site
5. Pair a supported wireless controller (I'm using an Xbox One Bluetooth compatible controller)
6. Plug BlueRetro Core into the DB25 breakout
7. Connect a voltage meter to ground on the breakout, and then test the voltage at each remaining pin with and without pressing a button (e.g. DPAD up/down/left/right, and A)
8. Write down the DB25 pin numbers and the names of the controller functions
9. Unplug the core, and power off for now
10. Search the internet for the DB9 pin numbers for Atari joystick connector pinout so you have their functions handy
11. Cut and strip ends of 8 wires of different colors long enough to connect the DB9 and DB25 breakouts
12. Be sure to first feed the wires through the included rings, and confirm their orientation.
13. Then connect the appropriate functions: up, down, left, right, fire, framing ground, signal ground, and voltage in  (VIN) to +5V supply from Commodore/Atari
14. Minimally connect, and test the functionality first with meter, then with Commodore/Atari console
15. Once verified working, finish connecting wiring stress-relief, bolt the enclosures closed, and otherwise button-up and tidy up the solution.
16. Play games!

DB25-1   to DB9-4   (right)

DB25-4   to DB9-3   (left)

DB25-GND to DB9-GND (frame ground)

DB25-7   to DB9-7   (VIN to +5V)

DB25-8   to DB9-8   (signal ground)

DB25-13  to DB9-6   (fire)

DB25-15  to DB9-1   (up)

DB25-17  to DB9-2   (down)

Another link to support this wiring is the BlueRetro Hardware Design documented over at hackaday.  There are schematics showing signal ground and VIN with the DB25 pinout.

I had fun with this effort, and should be able to expand this effort to support a second controller simultaneously connected to the same core, or wire up adapters for other systems myself.

The cost of the solution for me was about $22 with shipping, and as I was careful to choose items shipped directly from AliExpress and live on the west coast of USA, received the items quickly in about a week.  While this didn't save me the labor and only saved $3 from the Amazon solution, I learned a lot and feel comfortable leveraging the result to make solutions for other consoles and a second player.

(Any of you worried about 5V tolerance on the ESP32 or the buffer chip included with BlueRetro Core?  The Commodore is at 5V, and while the ESP32 is powered by 5V its IO is exclusively 3.3V.  It works for me without any additional consideration, but your mileage or concerns may vary.  You can usually get away with it for ESP32 as many of the IO are designed to survive 5V, and a 3.3V high signal does read as a high signal with most 5V systems.  So am I just getting away with it?  Maybe.)

But wait! Some keyboard lines are not working. I'm not done yet!

So with some prototyping, it turned out that the circuit to the Vic-20 needed to be open drain instead of push-pull. Pulling down was fine, but something was amiss with pushing 3.3V (or even 5V with other attempts) from the ESP32 BlueRetro Core circuit.

How does an Atari style joystick work anyways? There are 4 directions and one extra button. When any of them are active, the associated line is connected by a switch to ground. The BlueRetro Core simulates this by pulling to ground just fine, but when idle, it is pushing 3.3V. And the Vic-20 has its own 5V pull ups. That does sound messy. Somehow (without looking at the various schematics) this appears to cause a conflict so the 2, 4, etc. and F7 keys for example don't work anymore, they can't pull down to ground when this joystick circuit is attached.

So let's think how to correct this.  We want the connection to ground when the joystick is active, but we want high impedance (appear disconnected) when the no direction or selection is made.

The solution is a circuit that can perform this.  At first I'm thinking I don't have any FETs left over from previous projects, but finally after using one of my go-to buffer chips in breadboard circuits trying to solve this thing, I finally remembered that instead of being annoyed there are enable inputs for each buffer, the enable inputs can function as the inputs from the BlueRetro Core.   They are enable low, so when the joystick selection is made, the circuit will connect, and can take a grounded low input and buffer that to the Vic-20 joystick port.   So when the button or movement is made, the circuit will be grounded low, but otherwise that individual circuit is disabled (high impedance) as if the switch is not connected.  And this separates the 5V Vic-20 circuit from the 3.3V BlueRetro Core (ESP32) circuit.  And best of all, testing on breadboard, it works great!   The keyboard is now functioning normally with the joystick circuit powered and connected, and is still self powered from the Vic-20.

The revision to the above wiring is to connect DB25 joystick lines to OE/ lines of a SN74AHC125N, connect ground to the A lines, and connect the Y lines to the appropriate DB9 joystick lines. Also connect 5V power (14) and ground (7) to the appropriate IC pins.  And since there are five joystick lines, and this is only a quad (4) buffer part, we're gonna need two of them (and three if extending to two joysticks for dual player such as with a C64 or Atari 2600 VCS).  I recommend setting the unused enable lines for the extra buffers high (5V) to disable their outputs.

Again, these buffers are only for up/down/left/right/fire(select).   The voltage and ground wires should be wired between the DB25 and DB9 without buffering.