V. Ryan © 2002 - 2009

When building a circuit it is a good idea to treat it as being made up of modules or parts. For example you may want a circuit to be composed of a switch and a bulb. To make it easier to design the circuit it is better if it is treated as two separate parts, a switch circuit and a bulb circuit. These are then joined together - to produce one completed circuit.

Circuits are often built as modules with each doing a specific job. For example, a sensor module, a transistor module, a buzzer module etc...... When these are connected together they become a single integrated circuit.


Two simple modules are seen opposite and they are clearly labelled. They can be rearranged to produce a complete circuit. When the switch is pressed the bulb lights (see below).
Each module has a top rail which is positive and a lower rail which is 0 volts or negative.


The modules are linked together by electrical wires and they fit into the positive or negative connections on the electronic boards/modules.
Different makes of electronic kits are available and each allows pupils to build up circuits, test them or experiment and finally to dismantle the modules so that another pupil can use them in the future.
In this way circuits can be built without the need to solder and without wasting time linking each individual component using traditional methods.




Below is a temperature sensor circuit. When the temperature falls the resistance of the thermistor falls and a bulb lights. Notice how the modules are put together to form the completed circuit.


The temperature sensor is connected to a transistor which is then connected to a bulb. The transistor allows sharp switching of the bulb so that when the temperature falls the bulb comes on immediately and when it rises it goes off just as quickly. Can you draw the circuit as a circuit diagram ?




Below are some modules that can be put together to form completed circuits. Cut them out with a scissors and join them to complete the circuit questions on Sheet 3. If you require any modules that are not on this sheet, design them yourself and add them to the ones below.


1. This question refers to the example ‘temperature sensor circuit’ near the top of this section.
A. Redesign the transistor module and bulb module so that they form one module.
B. Draw the completed temperature sensor and transistor/bulb modules connected together. Explain how the completed circuit works.
C. Draw a new temperature module, this time one that ‘triggers’ the transistor module when the temperature rises.

2. A. It is found that the bulb in the completed temperature circuit does not light because the output of the single transistor is too weak. Design a new module that will provide a stronger output.
B. What is this new module called ?
C. Explain how this circuit works.

3. Design a ‘potential divider’ module. The module is for a nine volt supply and should allow six volts to be drawn from it.

4. Design a simple game or toy for a very young child. It can involve sound, lights, a motor etc... Produce a simple, clear diagram and an explanation.

5. Design the circuit(s) for the toy using modules and then draw the completed circuit as a ‘circuit diagram’.
You may need to design your own individual modules. Look at the photocopied sheets that have been given out in previous weeks. (Suggestion - show your knowledge by using relays, LEDs, motors etc... alter sensors so that they can be incorporated). Note, it is possible to set up components in ‘parallel’ so that they work together. (example seen below).



Remember to show your understanding of components such as relays and circuits that include ‘Darlington Pairs’ etc.... The examiner cannot give you marks for your understanding of electronics if you do not show it on paper.