|Chapter 1 - Overview & Introduction|
In this investigation I plan to study an interface which I built for the Macintosh called
'ElectroMac'. For the rest of this chapter I will introduce interfacing in general.
In the later chapters I will then go on to describe ElectroMac's hardware, firmware
and software. In chapter 2 I will describe the hardware and firmware, in particular
the command set used to communicate with ElectroMac. Finally chapter 3 will describe
the software I wrote for the Macintosh to control and communicate with ElectroMac.
Interfaces are all around us in one form or another. They allow computers to control
electronic circuits. The best example of this is traffic light control, computers and
video cameras are used to monitor traffic throughout the city. There are sensors in
the road to count the number of vehicles. The computer cannot normally receive this
data and turn on and off the lights. There is an 'interface' between the computer
and the lights, allowing the computer to switch the high voltages.|
Very often interfaces are part of the computer system rather than a separate unit. A separate interface 'box' is more often used in an experimental environment such as in a laboratory, classroom or workshop. These have general purpose sockets allowing the user to easily connect and rearrange the connection of devices.
Interfaces can also monitor Analogue signals - a range of voltages rather than just on or off. This could be used to monitor temperature, pressure, position senors, speed sensors. A good example of this is something like the UK super car, Thrust SSC which broke the land speed record. During the test runs sensors were placed all over to measure every little change in the car. Sensors measured the stress and strain in key areas of the car, and fed the results into the computer. These could then be analysed after the trial run.
Unfortunately there are very few electronic interfaces available for the Apple Macintosh computer and the ones that exist are very expensive (£200-400). For this reason I decided to build my own interface called ElectroMac. It has 8 digital inputs and outputs and 2 analogue input and output channels. It connects to the Macintosh via serial (Modem or Printer ports).
©1998 Nicholas Humfrey <e-mail> <www>