Building an

Atari 2600 Indy 500 Controller

 Aquí en español.

In this page I show how I built a controller to play with the Atari 2600 Indy 500 game. This game can’t be played with the standard controller, but only with its own special one. The working of such a controller was a mistery for a long time, until I saw the diagram on a WEB site, and I finally was able to start the design of an alternative controller. I show the entire project’s development in this page.

To the right you can see two pictures of the controller, front side and back side. I used an old Wico stick with fixed shaft in a way that only the shaft can rotate. At the right extreme you can see the acelerator microswitch, and below you see one of the boards that supports a slot optocoupler.

Now it’s clear it’s an optical system, in which I used two slot optocouplers, activated by a toothed cardboard disk.

Well, the important thing is it works, and how! I can play the Indy 500 at last, after years of being in possession of the cartridge.

And, of course, it’s Made in Chile.

Here you see a game screenshot, and an original’s controller:

 

 

How does it work?

The working’s mistery was unveiled when I saw the following diagram at internet:

 

You can infer that it’s enough by applying 2 bit Gray code to the Atari connector pines 1 and 2, a code that is repeated 4 times per revolution. Then, there’s the option of using some mechanical rotational system that generates such a code. Thanks to my experienceness in arcade steering wheel optical systems, I could easily  see the required system.

Mechanism Design.

The Gray code here requested can be generated by using a toothed disk that goes through two slot optocouplers. In this case I used the H21A2. Here is the datasheet. The disk must have four tooths and the optocouplers must be separated 67.5 grades, according the following scheme:

 

 

 

Next, I used a old Wico stick to which I fastened the shaft in a way that only could be rotated. It’s  enough by rivetting two washers at each stick extreme. I cut the switches supports and I screwed an aluminium angle with a 67.6 grades bend, in a way that the optocouplers stay in the right position (see photo).You can see a preliminary design cardboard disk.

You gotta be witty in order to hold the disk, by inserting washes or tiny plastic tubes in a way that it stays firmly, but it can rotate. Notice that just under the E-ring there is  a rubber washer, that allows the disk to rotate along with the shaft.

This is some kind of raw, but take into account it’s only a prototype.

 

The electronic part.

 Next, I designed the main circuit, using standard designs for these optical systems.

Parts List:

BC547 x 2

LED x 2

H21A2 x 2

R 1K x 2

R 4.7K x 2

C 0.022 uF x 2

Connector 9 pin

Cable 6 hilos

Appropriate print board x 2

Notice the circuit was assembled on two boards, one for each optocoupler, in a way they can be positionated in the right angle. I also installed a microswitch for accelerating (see below photo at the right). The final assembling look can be appreciated in the following photos:

Once the assembling is done, the LEDs turn on and off can be summarized with the following table:

A nice Gray code.

The final prototype working is perfect. Very easy to drive, soft and precise. It’s amazing given the level of the technology at the times this game was conceived. Compared to some “marvellous” today’s driving games of  PSX, N64, DC, etc. (some of which are non-playable), this controller design is a master work.

I haven’t tested this controller in an emulator, though if it works in the original machine, it should work in an emulator too.

If someone decides to build this controller, please write me and comment his results.

Some sites where I got the necessary information for this project (there isn’t almost even):

http://members.aol.com/~Atari7800games3/drivingschematic.jpg

http://www.atariage.com

My thankfulness to Khryssun, for asking for it, and to Mitch for publishing it.

Comments, critics, congratulations, disqualifications or whatever message to [email protected]

You can visit my other pages:

http://es.geocities.com/gamemasterquilpue/myownataricart.htm

http://www.ericzone.50megs.com

Home

Quilpué, 19/10/2001