An installation by Rob Godfrey
Commuter is designed to run under its own volition via the data its sensors pick up and by the way its different control systems interact with each other. These sensor and control systems are closely modelled on the human nervous system.
There is a lot of interaction between the human autonomic and somatic nervous systems. For example, if you were walking in a forest and encountered a ravenous tiger the somatic system would first sense the danger, the autonomic system would increase heart and lung rate and produce adrenalin, the somatic system would work towards escaping the danger. Commuter's peripheral nervous system interacts in exactly the same way.
At this point it should be stressed that the workings of the human brain are still not fully understood. From what is known, though, it appears that the brain does not consist of one central processing unit, but rather a number of processors that work together. Commuter's brain consists of 12 microcontrollers (tiny computers) which are all linked to each other. Each of the nine trains has its own microcontroller. The remaining three microcontrollers, hindbrain, midbrain and forebrain, reside beneath the station.
Commuter's 12 microcontrollers are all BASIC Stamps, manufactured by Parallax, Inc. These microcontrollers get their name from the language they are programmed in, PBASIC, and because they are about the size of a postage stamp. BASIC Stamps are very adaptable, easy to programme and hence are widely used in everything from industrial control applications to hobbyists projects. The forebrain, midbrain and hindbrain all contain a BS2p40, which has 32 input/output pins, can process up to 4000 lines of programming code and can carry out 12,000 instructions per second. The nine trains each contain a BS2, which has 16 input/output pins, can process up to 600 lines of programming code and can carry out 4000 instructions per second.
All of the sensors, devices and microcontrollers have an individual address and 'talk' to each other by means of asynchronous serial communication via the tracks. This means that the tracks have to handle 218 addresses. For this reason, 8 bit serial communication will be used because it can handle up to 256 addresses. This large data flow is not time critical in digital terms; ie, the microcontrollers process information in milliseconds (thousandths of a second); whereas Commuter works at its fastest in tenths of a second. Typically, the sensors will send a new report every 15 seconds. Digital control of the trains involves keeping the tracks permanently energised at 24 volts AC. All the addresses will have to work across this voltage.
Commuter's electrical system can be categorised into three separate areas:
The system has a maximum load of 1856 watts, which means that it can be easily powered by a standard 15 amp plug-in mains supply. There is also an option for Commuter to run under battery power, using a 12 volt, 38 Amp Hours battery (giving approx 8 hours running time using power management).
Lightscape - Commuter's lighting effects work in co-ordination with the soundscape and train motions/moods. There are 40 small blue lights beneath the perspex station platforms, which represent the brain. These blue lights are triggered by the sensors and devices; ie, if Commuter is very active its brain will be flashing very quickly, and vice-versa. There are also 50 small red lights spread around the rest of the installation. The trains have clear lights within them which shine through the transluscent carriages and show the colour of each train and reflect its mood. In total, Commuter has 210 lights, all directly linked to the microcontrollers and digitally controlled.
A big red button - the carriages in each of the nine trains are permanently joined together, and so for maintenance purposes, or when Commuter is being transported, the trains have to be driven off the installation into their own containers. To enable this a 'big red button' is built into the electronics. Pressing the button will disable all of Commuter's systems and will enable the trains to be driven by an operator. At times this button could be misused, to allow an operator to simply 'play with the trains'.
Big Red Buttons aside, Commuter can be likened to a basic organism: on an unconscious level it reacts to its environment. This could be achieved with much simpler electronics. The reason for the complex nervous system is because it's one component of the attempt to give Commuter consciousness - also known as artificial intelligence.