6 Controlling things; selling things

6.1 Controlling things

As you learned in Section 1, computers can collect, process, store and distribute information. This section shows that they can also be used to:

• control machines and simple mechanisms;
  


• conduct a special kind of commerce: selling on the web.
  

Let us examine more closely that common household appliance, the automatic washing machine. Virtually all such machines sold in the last decade or so are controlled using a microcomputer of some type. Before that, such control was provided by mechanical systems. However, because these had moving parts they suffered from wear, and tended to break down frequently or require replacement. Also, the nature of mechanical control systems limited how complex they could be. Consequently, they tended to be quite simple, and therefore less ‘automatic’.
The main tasks of a microcomputer in a modern washing machine are to:

• present an interface to the users that lets them know what possibilities there are and what the current state of the machine is;
  


• allow the user to select one from a variety of predetermined washing programmes;
  


• change some of the parameters (such as water temperature) to suit particular conditions;
  


• initiate, control and finally halt the actions of the machine in accordance with the wash programme selected;
  


• in some machines, ensure that the washing is done efficiently with minimum inputs of water or washing powder, in the interests of reducing resource use and maximising environmental protection;
  


• ensure safe operation of the machine.
  

Let's examine some of these tasks in more detail.