Switch-type joysticks for Atari and Apple. Tom Riley; Kelda Riley.
Switch-Type Joysticks for Atari and Apple
This month we are going to look at some homebuilt joysticks for Atari and Atari-compatible systems. We will describe two different designs for Atari joysticks:
One is similar to the commercial unit, but the other is a new type of joystick that can be customized for individual hand fit and high-speed action. We also include the electronic circuit needed to wire these Atari joysticks for use on an Apple computer.
The Electronics Of The Atari Joystick
The Atari joystick is simply a collection of five normally-open momentary-contact switches. These switches allow the computer to detect movement in eight directions and to read the input from a fire button. Four of the switches are paired so that only one switch at a time can be pressed. One pair controls up and down on the screen, the other pair controls left and right. The switches are paired by mechanical linkage rather than by electrical circuits. The fifth switch, the pushbutton, is mechanically independent of the others, but all share one common electrical conductor.
This construction is completely different from that of Apple-type joysticks, which feature two lever-controlled variable resistors. The Apple type are analog input devices, having many values over their range, while the Atari type are digital, with only a few discrete input commands.
In an Atari joystick you need precise control so that you can give an exact command every time, good feel so that your hands don't tire, and, above all, speed. Another helpful feature, but one that most commercial joysticks for the Atari lack, is tactile feelback, which means that there is a definite sound and feel when electrical contact is made. The joystick should also have good mechanical strength to insure long life, since it will see heavy use.
The most common commercial units for the Atari do not meet the above requirements. They are often awkward to hold, particularly for lefthanders; it is difficult to tell when contact is made; and handle movement is limited and rubbery. We think you will have a much better joystick if you build your own. Construction an Atari-type joystick may seem to be a somewhat mundane exercise, but working out the details of precise, rapid hand movement makes this task an excellent lesson in man/machine interface.
Features Of Two Homebuilt Units
Figure 1 shows sketches of two joysticks for the Atari. Each unit is constructed from a block of hardwood in which the switches and wiring are embedded. The hand grip joystick, like the standard unit, is used by holding the block in one hand and the grip in the other. The fire button on top of the handle will feel natural to most players. The weight of the homebuilt unit improves the feel, and the switches click to give you tactile feedback.
To operate the tipping disk unit, you hold the block in one hand and work the fire button with the index finger of that hand. (Your index finger can press a button more quickly than your thumb.) With the finger tips or palm of your other hand you press the disk to direct the movement. With the tipping disk joystick, the player controls the computer with hand movements that are quite different from those of the conventional units.
Construction Of The Hand Grip Joystick
Figure 2 presents a side view of the component parts of the hand grip unit. The base is a hardwood block that you make by gluing three 3/4 thick boards together. We used oak for all the wooden parts of the prototypes, but any attractive wood free from cracks and large knots will do as well. You can use clear pine, but the finished unit will not be as strong or good looking.
Cut the microswitch grooves with a dado blade in a table or radial arm saw (or use a router or handsaw). Since it is somewhat difficult to cut grooves in this small a block with a power saw, you might want to start with three 14 x 3 boards. Apply carpenter's glue and clamp them together. Drill the large holes and cut the microswitch grooves for four blocks into the one large piece. This accomplished, you can saw the large piece into four blocks. This is easier than trying to work with a small block and increases your cost very little. If you want to make only one joystick, choose the best of the blocks and discard the others.
Cut out the large central hole with a hole saw in an electric drill or with a large adjustable auger bit in a brace. It is easiest to do this before the grooves are cut.
The rubber hose shown in Figure 2 serves as a flexible joint. It is the type used for automobile heaters and was purchased at an auto supply store. Other types of hose may be used if they are springy and not too stiff. Size the wood plug and the base for the hand grip for a snug fit in the hose.
The hand grip was cut from a single piece of 3/4 thick lumber. With a wood rasp, contour the front of the grip to fit the fingers of your hand. The microswitch groove was cut with a small handsaw and a 1/4 wood chisel. If you prefer, you can move this switch to the front of the grip so that you operate it with your index finger rather than your thumb.
The hole down the middle for the fire button wires was drilled was a 1/4 paddle drill.
Drill the hole for the wood plug and then carve out part of the bottom of the block to make a cavity in which to place the wire connectors. Glue the plug in place. For the wire of each microswitch drill a 3/16 hole; drill a slightly larger hole for the main cable. All of these holes lead to the bottom cavity.
Rasp off the outside corners of the block. (The amount of rounding off you choose to do is one aspect of customizing your unit.) Sand all surfaces smooth, taking special care with the hand grip. The best finish for the wood parts is two coats of polyurethane varnish.
The Tipping Disk Joystick
The construction of the tipping disk is much the same as that of the hand grip unit. If anything, the tipping disk is easier to build. Figure 3 shows details of the parts. Cut out the three pieces of hardwood and glue them together. As noted before, it is easier to make several blocks at once and cut them apart later. Drill the 3/8 central hole and cut the microswitch grooves, following the instructions for the hand grip unit.
The groove for the fire button is on the side of the block; in Firgure 3 it is shown for right-handed players. The right- or left-hand orientation of the unit is set when you cut this groove and the hole for the main cable. To locate the groove properly, hold the partially finished block in your hand and find the most comfortable place for your index finger.
Drill the holes for the wires and the main cable and chisel out the bottom compartment as before. Round off all outside corners until the unit rests comfortably in your hand, and sand all surfaces smooth.
The tipping disk itself is made of masonite or other thin material.
It can be any diameter that suits you, either larger or smaller than the base block. Cut it out with a coping saw, and round off and smooth the edges. The disk and the block should be finished with polyurethane varnish before you begin wiring the unit.
The tipping post is a short piece of 3/8 dowel, one end of which is rounded. The exact height of the post and shape of the rounded top affect the feel of the finished joystick; so it is one of the key elements for personalizing the unit. Do not glue this piece into the block until you have tried the action and shaped the end to get the response you want.
The springy foam cross that fits beneath the disk was cut with household scissors from 1/2 thick polyurethane shipping material. The thickness and shape of this foam piece is another important element in personalizing the unit.
Adjusting The Size
The dimensions given for both of these joysticks will produce a unit that fits an adult's hands. Smaller hands will need a smaller block. You can reduce the 3 square dimension of the block to as small as 2 1/4 for the tipping disk and to 2 1/2 for the handgrip unit. The smaller blocks are somewhat harder to wire. If you cut a wood block large enough to make three or four units, you can cut them down to the exact size you need. (Remember the woodworker's lament, "I've cut if off twice already, and it's still too short.')
The key electrical parts of these units are the switches; they are, in fact, almost the only electrical parts. Radio Shack Submini Lever Switches were used for the prototypes. Discount mail order houses like PolyPaks (16-18 Del Carmine St., Wakefield, MA 01880) have similar switches for about half the price. Look for those described as "leaf' microswitches. The size of these switches and their terminals varies; so it is best to have them in hand before cutting the microswitch grooves in the wood block. Since the hinges on the Radio Shack switches (and probably most others) are a bit weak, they were strengthened with a matchhead size dab of silicone sealant.
The cable for each unit requires six conductors. We used two runs of four-conductor telephone cable with stranded wires, but you could use any small, flexible six-conductor cable.
The plug for the homebuilt Atari joystick is a DE9S socket from Jameco Electronics; it is a first cousin to the RS-232 socket used on many peripherals. The hand-wired version of this socket requires a separate plastic hood. The two plastic tabs on the hood stick out too far and must be filed down. The two clamping screws included with the hood are not needed for this project.
Distinguishing plugs from sockets on computer equipment can be confusing. A connector is a plug if the small metal parts that conduct the electricity are metal prongs. It is a socket if these small parts are receivers for the prongs (note the letter S for socket in DE9S). Either type of connector may be mounted on a cable or in the electrical device itself. Be careful not to order the wrong type.
Figure 4 is the electrical schematic for any Atari-type joystick. Each of the five microswitches is wired as a normally-open, momentary-contact switch. All of their common terminals (a small c identifies them) are connected and wired to pin 8. Each switch has its own wire on the normally open (n.o.) terminal.
To install the switches, solder two 3 pigtails of insulated wire to each switch. Telephone cable wire is excellent for this purpose. Use one wire color for all the common terminals and five different colors for the normally open terminals. Poke the wire through the holes. Position the switches with their hinges toward the center on the disk unit and down on the hand grip unit. The switches on the hand grip unit should just touch the rubber hose in its central position.
The switches were wedged into place in the grooves with flat slivers of wood from a popsicle stick and fixed in place with silicone sealant. Apply only a small amount of sealant and let it set for a few hours. (When you have completely checked out the joystick you can add more if necessary.)
Now turn the block over. Trim the wires short, but leave enough length to make the solder joints. Bring the main cable into the cavity and strip and tin all wires. Group all the common wires together, twist them, and solder the joint. Solder each of the five other two-wire joints, wrap each joint with a small piece of electrical tape, and press them all into the cavity.
Strip and tin all the wires on the socket end of the cable. Pass the cable through the hood and solder each terminal. It is easier to solder the socket if you clamp it upright in front of you in a small vise.
Checking The Circuits
You can use a multimeter set on a low ohms scale to check the wiring. Place one lead on socket terminal 8 and with the other lead move in turn to terminals 1, 2, 3, 4, and 6. On each terminal, press all the switches to be certain that the correct switch, and only the correct switch, shows continuity when pressed. Examine the socket solder joints for solder bridges and cold joints covered with dark resin. Make any necessary repairs. Don't assemble the connector until you are entirely satisfied with your work.
Turn off your Atari. Plug in your new joystick and turn the system on again. If it doesn't start up in the normal way, turn it off immediately and recheck your work. Then run your favorite game to try out the unit. If you get crazy responses, you have probably wired some of the switches to the wrong connector pins.
When the switches work correctly, you can put the finishing touches on the new joystick. The hand grip unit could probably use more silicone sealant on the switches and on the main cable where it comes out of the block. In addition, you can fill the bottom cavity with sealant, cover it with a piece of plastic, and clamp or weight it to a flat surface. After the sealant has set overnight, peel off the plastic, trim any excess sealant, and glue cotton felt to the bottom with contact cement.
The tipping disk unit deserves some personalizing touches. First secure the switches, main cable, and cavity as above. Then try out different combinations of thickness of the foam cross and height of the tipping post and shape of its top until you get a response you like. You can even do without the post altogether, or you can eliminate the foam by gluing the disk to the post with silicone sealant. Use whatever combination feels good and improves your spped. When you get the combination you like, glue the foam to the block and the tipping disk with contact cement.
Atari Joystick Circuit For The Apple
If you own an Apple computer you may want to make an Atari-type joystick for playing games that require only limited directions. "Snoggle' and many other arcade games are more enjoyably played with Atari-type joysticks than with Apple joysticks because the former have faster response. The resistance values of the two potentiometers in such a paddle, however, are limited to "full on,' "average,' and "full off.'
The construction of this joystick for an Apple is almost the same as it is for the Atari systems, except that you will have to make the bottom cavity slightly larger. Figure 5 is the schematic for wiring the unit. Note that two of the switches (down and right) use the normally closed (n.c.) terminal. The resistors R2, R3, R4, and R5 can be placed on a postage stamp size piece of printed circuit board and hidden in the cavity in the block.
Resistor R1 can be placed in the header plug so that only a four-wire cable will be needed.
This circuit works by mimicking a pot, using two resistors and two switches. If you don't press a switch, the game control inputs see the 68K resistors and read approximately 128. If you press the left (or up) switch, the game controls see zero resistance and read 0. If you press the right (or down) switch, the controls see 168K (68K plus 100K) and read full scale, 255.
Resistors R3 and R4 are not absolutely necessary, since the game controls read full scale when open, but it is easier to understand the circuit if they are shown. The stacked plug and socket we described in a previous article ("Multiple Socket Extensions,' Creative Computing, May 1983) works very well with the Apple-adapted joystick.
You can build joysticks for the Atari in a home or school workshop.
The materials will cost you less than the purchase of a commercial joystick, and the great advantage is that you can personalize your joystick for the exact feel and action you want.
Next month wew ill show you how to build a pair of race car steering wheels. Using these controls makes auto racing programs much more realistic and opens up the prospect of software for two-person competitive racing.
Photo: Figure 1. Joystick sketches.
Photo: Figure 2. Atari joystick.
Photo: Figure 3. Tipping disk joystick.
Photo: Figure 4. Microswitch Atari joystick.
Photo: Figure 5. Microswitch Apple paddle.