Omega Race Digital Spinner : A New Optical (non contacting) Replacement for POT
News Flash !!! As of Oct. 15, 2008, the ORDS spinner is available for ordering.
Complete plug-in solution for $50 USD + shipping. No taxes.
Options #1 $30 and #2 $60 described below.
If you would like to purchase the new spinner, email me with your request.
The new spinner board comes with a simple wiring adapter as shown below if you are ordering for either a fullsize upright or a Mini (caberet). The adapter plugs directly into an original power connector of the game. The data connector of the harness plugs directly into the spinner board so that no adapter is required. I cannot supply an all-in-one power connector harness like this for the cocktail or the cockpit cabinets. For these I supply the 2-position connector with 18" wires that you will have to connect to a +5V supply and to ground anywhere within the machine that you can locate them.
For the full size upright:
For the Mini (caberet) upright:
The ORDS board includes a few tiny lights (LED's) shown in the picture below at locations marked L1, L2, & L3. The lights provide a simple and quick way of verifying the basic operation of the device.
L1: Red - Indicates power is present.
L2: Green - indicates the logical state of channel "A" of the optical encoder.
L3: Yellow -indicates the logical state of channel "B" of the optical encoder.
The new ORDS board is a direct plug-in replacement for the original analog mechanical pot and the A/G converter board. Installation is easy, takes only a few minutes, and is worry-free because the connectors are designed to plug in to the original control panel wiring and only in the correct manner.
- unplug two original connectors at the control panel,
- remove the pot and mount the ORDS in its place,
- plug in the two control panel connectors to the ORDS board.
That's it. No soldering or wire cutting or splicing is needed and everything is undoable. The original wiring that runs down to the AGC board and the AGC board itself does not have to be removed. This means that you can switch everything back to the original configuration just as quickly and easily as it was converted to the ORDS in the first place.
- Get PDF File : Wiring drawing for the ORDS spinner in Omega Race.
Detailed installation instructions click here.
The ORDS spinner performance far exceeds that of the original pot & AGC board. If you are competing for the highest scores ever, you'll want this baby under your palm as your secret weapon. The engineers who designed Omega Race intended the game to be controlled in precisely this manner but they didn't have the perfect digital spinner encoder available. Well, it's here now and anyone can finally play Omega Race as it was truly meant to be played, with perfect precision and linearity, level after level.
There are no missing angles and the encoder is continuous therefore there is no dead spot at all and the ship control performs perfectly 1:1 with the knob. Besides superior control, the "feel" of the ORDS is exactly the same as the original pot.
Unlike the old pot spinner, there is nothing to wear out because the encoder is optical, not mechanical, so you'll never have to replace the spinner control ever again. If you play Omega Race often, you know how quickly the pot can wear out and how an intermittent pot ruins game play and reduces your scores. Further, even with a brand new pot, the dead spot moves (missing angles) to a different location with each new level. That's because the dead spot on the screen is relocated depending on the absolute position of the pot as it sits when the level begins. This means that the dead spot can end up practically anywhere making ship control limitations different for each level. The ORDS has no such inconsistencies and therefore ship control is perfect and the same from every level to the next.
Special Option #1: $30 If you want to use a different encoder that you already have, that's not a problem. You can order the ORDS without the on-board encoder (at the significantly reduced price) and with the external encoder port. Be very aware that if you go for this option that you must supply your own compatible encoder. I cannot accept returns with this option because I have no control over what gets connected to the board or how, not to mention the quality of the encoder that you choose.
This configuration comes with the 2-wire power adapter that is shown in other pictures. I will also supply a 4-wire harness that plugs into the encoder port. It will be like the one shown for option #2 except that the ends of the wires have no connector so that you may do with them what you want.
You might want to use an encoder that spins extremely freely (ball bearing mounted shaft) and doesn't have the feel (or drag) of a greased bushing such as that of the original pot or the new optical encoder. You can connect the desired encoder (or spinner) to a four pin connector on the PCB. The board will not work properly with an external encoder and the on-board encoder connected at the same time. Also, some encoders that you could source yourself might not work properly due to incorrect ppr values or output signal type. The ORDS supports 16 ppr or 64 ppr quadrature encoders only.
To configure the ppr setting for the board:
- 16 ppr : The split-pad solder jumper "SJ2" must be open (no solder, as shipped).
- 64 ppr : The split-pad solder jumper "SJ2" must be closed (soldered).
- Note: The split-pad solder jumper"SJ1" should always be left open (no solder).
To configure the encoder direction:
- Reverse (Count down as the encoder turns clockwise): The split-pad solder jumper "SJ3" must be open (no solder). This is the as shipped default configuration for correct operation of the encoders that the ORDS was designed for when installed in Omega Race.
- Forward (Count up as the encoder turns clockwise): The split-pad solder jumper "SJ3" must be closed (soldered).
- Note: The direction of the encoder may also be changed by swapping the channel A & B wires at the encoder.
To configure the ppr setting and the encoder direction using offboard switches or wiring:
- Leave all split-pad solder jumpers open (no solder).
- Connect wires (22ga max) from port terminals J5-2 and J5-3 to your off-board switches. Connect the other side of the switches to the power supply ground. If you prefer to use a ground point from the ORDS, you may choose from the following pins: J1-2, J2-9, J3-4, J4-5.
- The pins J5-1, J5-2, & J5-3 correspond to the split-pad solder jumpers SJ1, SJ2, and SJ3 respectively.
Special Option #2: $60 I can sell the ORDS board with the encoder adapted for offboard connection. You can order the ORDS with the new optical encoder not mounted directly onto the ORDS board. This way, you can mount the encoder in your game in the normal pot position with an absolute minimum of stress on it. The ORDS board can then be more securely mounted elsewhere and connected using a simple 4-wire harness that will be supplied. This will add $10 to the standard price due to additional parts, wiring, and labor required.
The ORDS board assembly is a new quadrature encoder and counter board of my own design. The ORDS board reads a standard 2-channel quadrature signal from the on-board optical encoder, counts the pulses, and outputs the counter value in Omega Race formatted Gray code. The board counts every edge of each of the two encoder channels meaning that it outputs four counts for each ppr (pulse per revolution) of the encoder. This makes the counter value immune to counting errors caused by vibration or electrical noise.
The PCB directly supports a specific Bourns quadrature encoder (the black box with the flatted shaft coming out of it). Because it is sealed, it is immune to dirt contamination. For the "encoder on-board" model, no wiring or connectors are needed to connect the encoder to the PCB.
The cost in parts is much more than half of the selling price (due to small purchasing volume). I'm not making enough profit on these to justify the effort so I probably will not produce more. Once they are sold out, that will probably be it.
These units are presently individually hand made to order. All units are tested before shipping. A two-player game (cocktail) requires two of these boards and you may have to run an additional wire to carry the +5V supply from one control panel to the other to power the ORDS on that side.
- Get PDF file : My interpreted schematic for the original Midway "Analog to Gray Converter board". I generated this by visual inspection of the board.
- Get PDF file : Functional description and calibration procedure for the AGC board.
- Get ZIP file from arcarc.xmission.com : Build your own digital spinner using an older design by Bryan Edewaard
The Omega Race game was designed by its developers to employ a spinner that outputs a 6-bit Gray code. The encoder however, was mechanical in its construction. Soon after the game was released, many of them suffered spinner failures because the conductive plastic tracks wore out from the electrical wipers dragging over them repeatedly as the player spun the control. The operators balked at the high cost of a new Gray type encoder that was known to wear out quickly, especially since it would have to be replaced several times during the game's life. The factory solution was to replace the Gray encoder with a simple pot followed by a custom ADC (analog to digital converter). The first conversion to the pot would cost the most because you had to purchase the ADC board along with it, but after that, you would only ever have to replace the worn out pot and that was cheap so in the long run it was a cheaper solution that achieved the same goal.
But wait a minute here... have you ever played Omega Race? Did you notice the "dead spot" in the rotation of the ship? That funny angle that you couldn't point to so you couldn't shoot that way so you died? You hated it right? Do you know why it is there? It's that stupid pot. You see, all pots have just one track and that track has a beginning and an end. The dead spot is the gap between the two ends. All pots have it and nothing can be done about it. This problem doesn't exist in Gray or quadrature encoders because each track provides simple on/off signals, not variable voltages, meaning that electrically, all points on the track that are "live" or "active" can be at the same voltage level and so the track can be made circular and continuous. Now you see their advantage. They have no gaps. They produce specific outputs for all positions all the way around in evenly spaced increments and because they are digital, the output is certain to be linear and proportional.
Ok, so the pot sucks, what can we do about it? Well, you could buy an encoder that outputs 6-bit Gray code, but remember, the mechanical ones failed miserably in the game in the past so it has to be an optical one. Um, good luck finding such a critter. Believe me, I tried. You could build one from 6 discrete optical sensors and a laser printed code wheel. That would be a lot of work and it would be big and ugly. It wouldn't be cheap either. Even if the sensors only cost $8 each, you'd spend $48 on those alone and you'd still have to come up with a way to mount them along with your new wheel and shaft and the original knob.
Just for fun, I bought a Bourns Gray code encoder, a mechanical one. It was stiff as hell and no good at all for Omega Race. Also, I found this out afterward, it didn't output standard Gray codes in the correct order. They were all mixed up. After I learned more about the nature of Gray codes, I also realized that an encoder had to be designed for the exact number of bits required. Gray code is not like binary code where you can just ignore the bits at either end of the scale that you don't need.
Then I considered quadrature encoders. There are optical ones readily available for relatively reasonable cost and I could add a simple counter circuit to produce the exact width and type of Gray code needed. This was my final solution for Omega Race and it's the device shown on this page.
Quadrature signals : The phrase "quadrature signal" typically refers to a pair of logic signals A & B where the signals are square waves offset from each other by 90 degrees.
CPLD : complex programmable logic device
VHDL : Very high speed hardware description language
What lead me to do this?
Prototypes built on a previous universal design PCB were installed and tested in Omega Race and they worked perfectly. In fact, they worked so well that I decided to design a new one. The prototypes were not designed originally for Omega Race so I did not widely publicize that design. The prototype board design was simply not Omega Race specific at that point. The new board that is described above was designed completely and specifically for Omega Race. More good news, the new board sells for much less than the prototypes.
This is my first CPLD project. It is based on a Xilinx CPLD chip and programmed in VHDL. I became interested in learning about programming CPLD chips a few years ago. However, it seemed a daunting task and I couldn't really imagine what I'd ever do with it once I learned it, so I never took the plunge. After I got into the arcade hobby a few years ago, I saw some of the wonderful new logic replacement modules and chips that were available for some games. There's the relatively well known "Atari AVG" replacement logic boards made from a dozen standard chips and there are now a few single chip versions of it. There are single chip replacements for certain Galaga/Pacman/Xevious custom IC's. Most of these logic replacement devices are built from modern Xilinx or Atmel CPLD chips. I have been programming microcontroller chips for many years but I had never attempted to create my own custom "hard logic" circuits within a programmable logic device before. I found some of the work being done by the infamous JROK quite facinating so I emailed him on the subject. He kindly advised me to think of logic design in a new way. That I did. I investigated hardware description language (specifically VHDL) which is kind of a "C" level programming language to create logic. I bought an inexpensive Xilinx CPLD development board from Digikey, downloaded the free Xilinx ISE software and I dove into the world of CPLD's. My first project beyond the development board is the one on this page. Now, after doing this project, I'm thinking of no less than half a dozen new projects. CPLD's are incredibly suited to the arcade hobby because they can replace large numbers of old chips and circuits. They can create almost any configuration of logic imaginable. They can even be used to create entirely new replacement CPU or ROM boards, or new multi-game systems, or new controller interfaces.
If you want more information or have questions. Just email me.
Do you think I would sell more of these spinner boards if I had named or described it thusly ?...