.
1P : rototype circuits

Learning about electronics demands a hands-on approach. Your understanding will develop much more quickly if you put theory into practice by handling and using electronic components. The practical work supporting Chapter 1 explains how to start building circuits in temporary, or prototype, form.

.
Navigation

Prototype board Circuits

Back to Contents

.
Prototype board

Look at the diagram below which shows a prototype board:

Components and wire links can be pushed into any of the holes. Inside the prototype board, metal channels with springy contacts make connections with the components, The metal channels are arranged in rows, as indicated below:

inside a prototype board

Some prototype boards have an easily removed base which lets you see this arrangement. On each side of the board, there are two long channels connecting from top to bottom. In the centre of the board, there is a gap, and on either side there are short channels, each corresponding to a horizontal group of five holes.

What connections are needed to make a circuit? First, you need to connect a power supply. The 0 V connection is made to one of the strips of holes on the left hand side of the board. Connecting leads with BLACK-coloured insulation are used. The positive end of the power supply is connected to the right hand side of the prototype board, using leads with RED-coloured insulation.

A power supply voltage of +6 V to +9 V is suitable for the circuits you are about to test. You can use a laboratory power supply, a regulated 'battery eliminator' supply (as used with a personal stereo), or a PP3 battery with a battery clip.

beginning of chapter Up

.
Circuits

Build the circuit shown below:

circuit 1: the simplest possible prototype circuit click for next stage

The lamp is connected directly across the power supply and should shine with normal brightness. If it does not, check that

The wires from the lamp need to be inserted exactly as shown. Check that the lamp filament is undamaged and that the lamp is screwed into the holder, making proper contact with the holder terminals.

This is like the torch circuit. Unless there is a continuous conducting path, current will not flow and the lamp will not light.

Change the circuit as follows:

circuit 2: using links to the power supply rails click for next stage

click to return Up to previous stage

Now you are using link wires to make connections from the power supply rails to the rows of holes in the centre of the prototype board. When wires are in the same horizontal row, the springy contacts inside the board make an electrical connection between them.

Here is a circuit which will not work:
circuit 3: a circuit which does not work click for next stage

click to return Up to previous stage

The lamps are supposed to be connected one after another, in series, but will not light up because the circuit is incomplete. Look at the prototype board layout carefully. Where have mistakes been made? Build this circuit and experiment, moving the lamp connections until both lamps light up.

Click here for a circuit which works. (Click the link just once.)
close button

To close the information window, click the close button at its top right hand corner.

Once you have got the circuit to work, what do you notice about the brightness of the lamps? How can you explain this result?

The pencil icon tells you that you should write something down about this.

Is more or less current flowing?

Unscrew one of the lamps from its socket. What happens to the other lamp?

The lamps are less bright than normal because the resistance in the circuit has increased. This makes it more difficult for current to flow. When one of the lamps is unscrewed, both lamps go out because the circuit is incomplete. In a series circuit, the current flowing at all points is the same.

Now build a different circuit, this time with the lamps in parallel:

circuit 4: lamps in parallel click for next stage

click to return Up to previous stage

Check your connections carefully.

How does the brightness of the lamps compare with normal brightness, as in the first circuit you constructed?

Is more or less current flowing in each lamp?

Has the current provided by the power supply increased?

Unscrew one lamp from its socket. What happens to the other lamp?

When the lamps are connected in parallel, there are alternative pathways for current flow. Each lamp operates with its normal current, so the power supply should provide twice as much. Both lamps ought to be just as bright as a single lamp, but you might find that they are slightly less bright, depending on the power supply used. Unscrewing one of the lamps does not cause the other to go out because there is still a continuous conducting path.

Your final prototype for this session includes a combination of series and parallel circuits. When the circuit is correctly assembled, all three lamps should light:

circuit 5: series / parallel circuit

click to return Up to previous stage

Are the three lamps equally bright?

How does their brightness compare with normal brightness?

What happens when individual lamps are unscrewed?

Experiment with the circuit and interpret your observations in terms of the overall resistance in the circuit and the currents flowing in each lamp.

beginning of chapter Up Back to Contents