A look at replacing the mouse on Non-ADB Macs (128k - Plus) and other Computers. The first part covers an electronic circuit to emulate a mouse and a second section looks at a couple of other devices and ideas.
••••• Part One.
••••• Sliced Bread.
A Joy Stick adaptor for Original Macintosh Computers, and others…
••••• Intro.
Originally I had planned to release this item as a commercial product but time, money and effort were short and although it got a bit of interest, I am unable to pursue the commercial side of this project but for this collection of files and the option of someone buying either the Printed Circuit Board, a kit of parts or a complete unit, assembled and tested.
In a simple fashion it forms a link between the standard Video Game Joy Stick, four switches and a Fire button, and a Mac’s mouse port. The PCB assembly has a standard DB-9 connection for the Stick and a lead and plug for the Mouse port. Speed control is via a Pot, or Knob, that varies the speed from a slow crawl to a brisk jog across the screen. This could be placed within easy reach of the operator and any arrangement of contacts can be substituted for the Joy Stick.
This has been ‘Play-tested’ by my son Chris, and myself, with Harrier II and Apache Strike over a period of a year or two on a 512K and 512Ke and seems to give little trouble. It may not be a complete replacement for a mouse for some people in all circumstances.
The Idea revolves around the way that Non ADB Macs get info from their mice. The series of electrical signals from mouse to Mac is called Quadrature, in this case two signals are used to get information about direction and speed for each axis, called X and X’ or Y and Y’.
In the diagram above we see that input 1 is low, indicating that a switch is closed, while input 2 is high which is the way that it would normally be. Sensing these conditions, the circuit generates the signals, Output 3 and Output 4. In some mice these signals are created using a slotted disc that interrupts a beam of light to a sensor, in my circuit a series of logic gates modify the pulses coming from a clock source. The difference between my circuit and a mouse is that a mouse varies the signals according to your hand movements, my circuit reacts to switch closures and speed can be varied by changing the original clock frequency.
Anyway, the Mac uses one signal of each pair to indicate if movement has occurred and then checks the condition of the second line for an indication of direct, i.e. left or right, up or down.
In the above diagram we can see how this is done. If we take Out 3 as our trigger and Out 4 as direction then, following from left to right, we see that every time Out 3 drops from High to Low, Out 4 will be Low, this might say to your Mac that we are moving from Left to Right. If we follow the signals from right to left we now see that when Out 3 drops from High to Low, Out 4 is now High, and our Mac can see that we are going the other way, Right to Left.
For those who know a little about logic the above diagram should need only the following explanation.
Switch 1 and 2 are the contacts in the average Video Joy Stick, the Lamps 3 and 4 represent the Outputs 3 and 4 and are the signals to our Mac. In the real circuit the AND gate is replaced by a Diode. Basically a switch closure enables the clock which generates the pulse to drive the rest of the logic, one Output signal is from D type Flip-Flop, wired to divide the clock signal by 2, the second D type Flip-Flop is also wired to divide the clock signal by 2 BUT it is feed with an inverted clock signal, and the output of this D type Flip-Flop is modified by an XOR gate, this allows the signal to the inverted on demand.
In the public domain there is a lovely application called DigSim 2.8, in a folder that is with this note is a couple of files that will enable you to see the operation of this circuit without having to buy anything. If you use the Application for any more than a quick look at these files then please send something to it’s Author.
The other Axis has the same circuit and uses the second half of the clock chip.
If you build your own circuit from parts and the diagrams from this doc, please be careful, Mac motherboards are expensive to replace. You can build a simple test circuit using a single chip, a couple of LEDS, resistors and a Voltage regulator IC. The chip that I have used was a 74LS74 and wired it up for testing in the following fashion.
Here the switches represent the Joy Stick and the Outputs are the outputs from the circuit. If all is well then moving the Joy Stick will cause one or the other of the LEDs to light, and the third LED should flash, often very fast, showing that pulses are coming out in the correct fashion.
••••• Part Two.
••••• Another Solution or Two.
If you require more control or if you want to use a more elaborate control mechanism then a device called a Rotary Encoder may be the answer. These devices can produce the Quadrature output signals using a coded disk and a set of contacts or sensors. The price of these devices vary according to type.
A simple contact type device will cost around $8 but an optical encoded device may cost over $100. An example to play with is made by Bourns and is part number #ECW0J-C24-BE00024. I bought mine from VSI-Promark for about $8. ( remember that you will need two). This is a very simple Mechanical device designed for PCB mounting, but others are available and you can connect wires using a small piece of 'Vero' board. It is the size of a standard Pot and is a couple of contacts and an encoding wheel, mounted on a shaft. To use this device to control the pointer, you connect the common terminal to Ground, the other two terminals connect to the inputs of an axis, either X and X' or Y and Y'. Then when you turn the shaft the pointer moves in the required direction.
The beauty of this device is that they do not require power. The down side is that the number of pulses per revolution of the shaft is quite low, 24 pulses/rev., which may or may not be a problem.
These devices could be mounted on a Mechanical drawing board to form a digitiser, of sorts, or link them to a Lathe and monitor the shape of the object being machined. Make a giant Trackball.
••••• Which Macs ?
Original Macintosh computers, 128K, 512K 512Ke and Plus, used this simple method of signally. Also this is used with some Amiga, Atari, IBM and PC clones. I think it was also used with the Apple IIe. So this circuit can be used with more than just an Old Mac.
••••••••••••••ShareWare and Copyright.••••••••••••••••••
Release 1.0
This file and the other files that are included in this release are Copyright 1992 Paul B Jones.
There is a Double-sided PCB and component layout available, with or without parts, this PCB is also Copyright PBJ.
••• Permission is given to anyone who wishes to use this design for their own private use, or to build devices for the disabled / physically impaired on a non commercial basis.
PCB and Layout: $10
PCB, Parts and Layout: $25
As above assembled and tested: $35
Complete, in the Box: $55
All prices are including Sales Tax and postage in Australia.
Elsewhere send the same in US dollars.
For more details write to me:
Paul B Jones
P.O.Box 208
Moora 6510
Western Australia.
other Hardware notes.
Chips used:
74S124 or 74LS629 Clock chip.
74LS74 D type Flip-Flops
74LS86 XOR 2 input gates.
I have not built this circuit using lower power devices but it should be possible.
Mac Mouse Port pins.
1 - Ground
2 - +5 volts. Be very Careful !!!!!!
3 - Ground
4 - X' ( Quadrature signal)
5 - X (Interrupt)
6 - No Connection
7 - The Button
8 - Y' ( Quadrature signal)
9 - Y (interrupt)
Below are the Pins for the average Video Game Joystick.
Do not plug a standard Video Game Joystick directly into your Mac.
