Connecting the Modules

You can connect the modules together by using the wire provided (cut it into suitable lengths and strip the PVC at the ends to bare the wires). The wire can be then routed between the 'chocolate-block' connectors and fastened with a screwdriver. Alternatively, you can use the wires terminating in crocodile clips to make the connections. This is faster than using just wire but can get very messy and hard to see what is going on so you may end up using a combination of both approaches.

A word about current flow. When electricity was first discovered, the engineers of the time did not fully understand it but knew that current flowed out of one terminal of a battery and back into the other terminal. They named the terminals positive (+ve) and negative (-ve) and said the current flowed from positive to negative This is called conventional current flow.. As it turned out, they got it wrong and current actually flows using excess electrons from negative to positive This is called electron current flow. I'm sure you are well aware of this but by the time it was discovered, so many books had been written saying current flowed +ve to -ve, that it was hard to change peoples thinking. Even today, most people use conventional current flow (+ve to -ve) and it really does not make much difference. So when I talk about current flow, I assume conventional current from +ve to -ve.

Making a Switchable Lamp

Let's wire the battery via a switch to a single lamp. This means connecting a wire from the +ve battery terminal, through one of the switches, onto a bulb and from the bulb back to the negative battery terminal. The picture below shows an example using the toggle switch although you could use one of the push switches instead. If you use one of the 6V bulbs it should glow yellow. Use the 3.5V bulb and it will glow bright white. This is because it is being driven from the 6V batteries so it is really being over-driven. You may find the 3.5 V bulb blows if used like this - so best to use the 6V bulbs. But don't worry if it blows, it's easy to get a replacement!

It gets quite hard to follow real circuits because wires tend to bend and twist all over the place so for this reason, we use circuit diagrams which simply describe the electrical circuit without worrying about how things physically look. They can be thought of as a 'map' of the electrical pathways that need to be connected together to make things work. Wherever you have electronic components connected together, there will always be a circuit diagram describing it somewhere. The wiring in a car, a remote control helicopter, even the inside of microprocessor used within a computer will have a circuit diagram somewhere describing how all the parts are connected together. Many circuit elements have 'standard' symbols, some are just shown as boxes with writing describing what they are. Here is the circuit diagram describing what you have just built (if you used a push-switch).

Wiring two lamps in series

Now let's try and wire two bulbs in series. This means that after the current has passed through the first bulb, rather than going back to the -ve of the battery, we send it through a second bulb and then back to the battery. Here is a picture of the series wiring. If you use the two 6V bulbs, you will notice they both glow more dimly than before. This is because the first voltage uses some voltage and the second one uses some voltage.

This is the circuit diagram. Note the different switch symbol. This is the toggle switch and this has three contacts, one is 'common' and it will connect to one or the other contacts depending whether the toggle is up or down. It can be thought of like railway points where the main track comes into the common terminal and can be switched to one siding or another, depending on how the points are 'switched'. You could run one bulb in one position, and another bulb in the other position. You can try this yourself later. Note there is one common terminal that can be switched to one of two other positions. In this example, we only use two of the contacts so the switch will be off in one position. Make sure you find the common terminal as the two other terminals never connect to each other.

You will notice the current flows around one path, first through one bulb, then the second. If you use your meter to measure the voltage across each bulb you will see that about 3V is present across each of them, so each 6V bulb is now only being driven at 3V which explains why they are much dimmer. You can safely use the 3.5V bulb in this circuit now as it will not be over-driven. If you try using three bulbs in series, measure the voltage across each and you will see it lower still. This is exactly how Christmas tree lights work. Christmas-tree lights plug into 240V. If there are 20 of them in series, then each bulb will have 240/20 = 12V across it. So the bulbs used on christmas lights are low-voltage ones. As they are all in series, if one bulb breaks, they all go out and to try and find the broken one can be tricky!