Introduction


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 Introducing Circuits explains how to start building circuits in temporary, or prototype, form.

Look at the diagram below which shows a

prototype board

Prototype board is used for building temporary circuits. Connections are made by pushing components and wire links into the holes in the prototype board.

prototype board, or 'breadboard':



Prototype board is used for building temporary circuits without soldering. Components and wire links are pushed into the holes. Inside the prototype board, metal channels with springy contacts make connections. The metal channels are arranged in rows:



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 running from top to bottom. There is a gap in the centre of the board, and on either side of the gap there are short channels, each corresponding to a group of five holes.

A power supply

voltage

Potential difference, or voltage V is a measure of the difference in energy between two points in a circuit. Charges gain energy in the battery and lose energy as they flow round the rest of the circuit.

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

A battery consists of two or more cells. The cells may be connected in series or in parallel.

battery eliminator' supply (as used with a personal stereo), or 4 AA size cells in a battery holder. Check the directions of the connecting channels by moving the mouse over the diagram:

Connect a lamp to the prototype board, like this:

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

• the power supply is switched on;
  
  
• the circuit is complete;
  
  
• the wires from the lamp are inserted exactly as shown;
  
  
• the lamp filament is undamaged;
  
  
• the lamp is screwed into its holder, making proper contact with the holder terminals.
  
  

This is like the torch

circuit

A circuit is a closed conducting path.

circuit in Introducing Circuits. Unless there is a continuous conducting path,

current

Current I is a flow of charged particles, usually electrons.

current will not flow and the lamp will not light.

Change the circuit as follows:



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 the wires are in the same horizontal row, the springy contacts inside the board make an electrical connection between them.

Build a new circuit exactly as shown in Fig.6:



This circuit will not work. The lamps are supposed to be connected one after another in

series

Components are connected in series when they are joined end to end in a circuit, so that the same current flows through each.

series, but will not light up because the circuit is incomplete. Look at the prototype board layout carefully. Where have mistakes been made? Experiment, moving the lamp connections or adding new links, until both lamps light up.

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

parallel

Components are connected in parallel when they are joined side by side in a circuit, so that they provide alternative pathways for current flow.

parallel:



Check your connections carefully.

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:



Experiment with the circuit and interpret your observations in terms of the overall

resistance

Resistance R limits current flow.

resistance in the circuit and the currents flowing in each lamp.

The joining wires which you use to connect up your circuit must be made from insulated single core wire, described in catalogues as '1/0.6 mm single core equipment wire'. To make the wire links, you need to remove about 5 mm of insulation from each end. This is done using wire strippers:

Adjust the position of the screw, tightening the locking nut on the other side, so that the jaws of the stripper do not close completely. The jaws grip and cut into the outer insulation without penetrating into the wire core.

Automatic strippers, shown below, are quick and easy to use and work well provided you are careful with them:



A pair of cutting blades in the handle lets you cut the wires to length. Place the end of the wire in the jaws against the adjustable stop and close the handles to remove the insulation. Cut links 50 mm long and keep them for reuse.