                About the Arcadia 2001 family's rear auxiliary controller ports


There has been some discussions lately about the "left and right auxiliary controller jacks" on the rear of Arcadia family consoles. Hopefully, this will answer all questions, or at least eliminate impossible situations from further consideration.

I opened up my Leisure-Vision yesterday evening, as promised, and got out my trusty voltmeter. Here is the verified, non-guess version of what the small expansion ports are or do, on the Arcadia family of consoles.

The first thing you have to understand is that there are only TWO WIRES connected to each individual port.

With only two wires, these ports can not do much at all. With only two wires hooked to anything inside, all that can be hooked up is a potentiometer -- in other words, a paddle controller. And by that, I mean a BARE paddle... not even a paddle and a fire button. There is absolutely no way in heck that another set of controllers can be added, like the ones that the console already has in place from the factory. Please take my word on it, and eliminate those possibilities from further consideration.

Yes, it does look at first like there are three places that wires can go, if you open up a console and just glance at the outsides of these small sockets. However, if you look inside the socket itself, and verify what you see with a meter, you will find out that the third wire is not what it first appears to be. The bottomline is that there are only two wires going to the PC board. Not three, not four, not ten; just two wires.

These sockets, by the way, are the kind that are made for audio plugs, such as you might expect to see on headphones for a walkman, for instance. (Except in mono, not in stereo.) I am not an expert on dedicated Pong systems, but I believe that a number of Pong-style paddles likely once existed, that used these plugs, making it all the more likely that that is what the designers originally had in mind. I for sure had an old Sears Pong machine at one time, that had paddles with audio plugs. (The raw connectors are still readily available, for today's do-it-yourself tech guys.)

WIRING

The RING connection (the long body of the audio plug, but not the tip of it) goes directly to the five volts supply on the main circuit board. And by directly I mean just that; both RING connections are wired to the output leg of a 7805 five volt regulator.

The TIP connection on the incoming plug is wired directly to the existing controller ports, at the back side of the internal connector that allows the controllers to be unplugged from the main circuit board. (While the controllers appear to be hard-wired to the board, from the outside of the console, that is not technically true. You may have to open the console's plastic case, and then also remove the heavy RF shielding surrounding the main circuit board, but they can then be unplugged.)

Tracing the wiring inside the controller, it appears the middle (sixth from either side) connection of a small PC board inside the upper end of the controller, is where the TIP connection ends up. (Although it is on the fourth wire on the back of the place where the controller plugs into the main PC board, but on opposite sides of each port; 4th from the right on the right side, 4th from the left on the left side. Apparently, they paid their Assembly Chimps to put up with the funky hand-wiring necessary. I guess this makes sense, as the main components of the controllers could be made with a single, reusable set of parts, with hand-wiring making the finished controller be a "left" or "right" side controller. Anyway.)

Tracing things further, we find that the middle or sixth wire on the small controller port PC board goes directly to the delicate, printed circuit traces on the clear plastic sheet parts of the controller's innards. It ends up being connected to a place on the directional controller or joystick, ignoring the fire buttons and keypad entirely.

The delicate printed circuit trace is part of the circuitry that figures out if a person is trying to move to the left or the right. It is hard to describe, without a picture, but there  are three sheets with traces. The bottom sheet has metallic traces facing upwards. There is a middle sheet, with shaped holes or cut-outs that help sheild some areas while leaving others exposed. A top sheet has downward-facing traces. When the user presses or moves something on their controller, it makes the top and bottom sheets touch one another, so that two wires touch internally. They made and folded each sheet in such a way that they act like a spring, naturally staying apart from one another, unless the user forces them to join, momentarily. (Pretty clever, actually!)

What does that leave us with? A confusing mess, since so far, as the main and rear controllers seem to be fighting to do each other's jobs. This is where that mysterious third wire comes in, on the rear auxilliary ports.

The THIRD WIRE is apparently a switch, of sorts, to determine which controller will be in charge of allowing the user to move something to the left or the right. 

The THIRD WIRE is permanently connected to the RING connection, at the rear socket, through a 150,000 ohm (or 150k ohm) fixed-value resistor. (Looks like 1/4 watt, with a gold band or 5 percent tolerance, and both measured well on mine.)

From there, the THIRD WIRE can either be shorted to the TIP or left electrically disconnected, depending on whether or not an audio plug has been inserted into the rear sockets. (The TIP has spring pressure, so it touches the THIRD wire until the audio plug physically moves it out of the way, breaking that connection.)

It is not always shorted, or it would not be much of a switch. It only connects TIP and RING (through the resistor) when nothing is plugged into the rear ports.

So if there is nothing plugged into the rear ports, then 150k ohms of resistance will always appear at the "left / right" part of the main controller's circuit.

(Emulator authors take note: I say "left / right part" because on the bottom sheet of mylar-with-circuit-traces, they are paired electrically. There is a single "left / right" connection that faces upwards, along with two seperate "up" and "down" wires, for a total of three actual wires on the bottom sheet. On the upper plastic sheet, are two more wires, both of which are part of an electrical pair. The upper sheet's "up" and "left" wires are one connected pair, while the "down" and "right" wires are similarly connected to each other. So the upper sheet only has two actual wires, for a total of five wires, making up the directional circuit. Note that this is arranged totally unlike the common Atari-style joysticks, with "up, down, left, right, and ground". This odd way of doing things probably has something to do with the odd error or glitch that Paul Robson had, when he wrote the first Arcadia 2001 emulator, where he said in his instructions that the directions sometimes seemed to change axis' on him? He never saw an actual console, as he wrote his emu from game source code, alone.)

The THIRD WIRE is not shorted to the TIP, when there is an audio plug in the rear sockets. The TIP physically moves away from the THIRD WIRE, making "no connection" there. Instead, the TIP runs directly into the main controller's circuit board, without any interference, so it's input will be read as controller movement.

When an appropriately-sized audio plug is inserted into the rear port, the RING portion is connected directly to the five volts source. The THIRD WIRE is not connected to anything, and the 150k ohm resister only has one end hooked up to anything, so it is technically not in the circuit at all, any more. It just "isn't there".

So far, with just an imaginary audio plug inserted, we do not have a complete circuit yet. It is presumed that the RING wire and the TIP wire, coming off of the audio plug, is then hooked up to a length of cable, with a potentiometer wired between them. At that point, we would have positive five volts running out through the RING, through the external potientimeter, and back to the main controller port output circuits, where it would be interpreted and acted upon.

SUMMARY AND CLOSING THOUGHTS

So, to sum up: if nothing is inserted into the rear ports, the overall circuitry is set to make the main controller ports "see" a ghost 150k ohm "potentiometer" or paddle hooked up, but not moving. If something is hooked up through the rear ports, then the ghost 150k ohm paddle goes away, leaving the real one in charge, instead.

I can only assume the designers would presume that if a paddle was in use, that the main controller would not be in use, so no "left / right" buttons would be pressed on that, then leaving the paddle controller completely in charge of moving left and right.

Before I forget to mention it: I did also confirm that the joysticks in the Arcadia family are only 8-way sticks, not the 16-way sticks some folks thought they might be. This is easily verified by tracing out the wiring inside a controller. Only five wires total are a part of the joystick portion of the controller. With five wires, you can not have more than an indication of up, down, left, right, along with one wire to complete the circuit. You can also have the four diagonals that occur when two of the initial directions are touched simultaneously, but beyond that, there isn't enough wiring present inside, no matter how you hook it up inside. Any 16-way joystick would need far more wiring.

What value of a potentiometer is needed, to make a rear port paddle for the Arcadia family? We're working on that. 150k is a good place to start experimenting, since that is the value of the fixed resistor that is being "seen" by the controller's upstream movement interpretation circuits, whenever no paddle is hooked up to the rear ports. (Whether this is a "middle" or "end" position is not yet known for sure, but experimenting with individual games could help to determine it. Better paranoid than smug, I always say, so I prefer to do some testing.) If any of you dedicated Pong guys have paddles like this, you may want to measure their pot's resistance?

This may also give us a solid clue as to why certain games act so oddly, at times?

If games were originally written with a potentiometer-joystick in mind, but were later given a digital, limited-positioning button-based joystick as input instead, well, of course they would "malfunction". But since most of us have little or no experience with more than the one console we own, figuring all of this out takes much time!

I guess we need to start looking into this more, if we want certain games to work well, on any one of the semi-compatible families of consoles within this console group. If nothing else, some of the Palladium-type games would likely work better on the Arcadia family, but we may also learn more and improve emulation efforts.

  -- Ward Shrake --

November 21, 2002