Robotics and real-time control :

Using the analogue computers

We have two identical analogue computers, and one power supply which can drive them both at once if required. They can be used together as a single computer if you want more facilities than are available on just one. Each computer comes in a labelled box, which should contain the computer itself, a manual, three power leads ( red, black, and blue, with large plugs on the ends ), and a lot of wires for connections ( smaller plugs ). The power supply should be stored in the cupboard with the computers, but has been known to wander away. It doesn't have a box; it's a smallish blue not-quite-rectangular object labelled FEEDBACK PS441, with a mains lead and a few sockets on it.

Read the manual; it's extremely elementary, but will do you no harm. It contains quite a bit of useful information. It wouldn't harm you to run through the experiments, though you might not need to do them all.

Setting up.

Connect the power supply to the mains; connect it to the analogue computer(s) using the three power leads, following the colour codes. You have to connect all three leads; even if you know you're only going to be using positive voltages, the operational amplifiers need the negative supply as well. ( Yes, I can try to be clever too. )

Connecting circuits.

Each computer is constructed as a collection of independent units, and you build up circuits by making connections between the units in the obvious way. You shouldn't be able to do any damage by making wrong connections, though it does no harm to think about what you're doing before doing it.

Make sure you know what you're doing when you make a connection. The manual includes several diagrams of circuits showing connections as heavy lines on a picture of the analogue computer board; don't just follow these slavishly. Instead, make sure that you know what you're really doing in terms of the computer components. Test your understanding by changing conditions and observing the effect - for example, if a diagram shows a connection to a 100kilohm input, try a 200kilohm input and make sure that you understand the result.

All the +15V connections are equivalent, as are the 0V and -15V connections; it doesn't matter which you use.

Measuring.

Use the wall-mounted meters ( switched to V ) for slowly varying signals. The meter flying leads fit comfortably into the computer's connector sockets. In some of the experiments, two meters are recommended; in practice, it's easier ( and less clutter ) to use just one, leaving the earth connection fixed and moving the other between points you want to measure.

For higher speeds, use the oscilloscope. The analogue computer manual brings in the oscilloscope later on, and the computers have provision for repetitive computation which makes it easy to display traces on the oscilloscope. It's a good idea to use them both together on a simple experiment ( perhaps the integrator ) just to convince yourself that the two are equivalent - and to check that you're using the oscilloscope correctly.

For the more advanced experiments, use the meters to set potentiometer values and the oscilloscope to inspect the results.