Amendments and supplementary information: Additional Applied Science Unit 5 and Unit 6
All through these supplementary notes, remember that you must carry out your own risk assessment and take suitable precautions.
Stelar is an educational charity providing education and training about wireless communications to educators. Visit their webpage to find our about courses, or to download Powerpoints and briefing sheets (e.g. on digital audio broadcasting). STELAR
A mobile, fully self-contained communications centre will visit schools and colleges up and down the country, free of charge. Interactive sessions can be designed specifically for Ap5 and your students. A space satellite dedicated for schools use is also being developed. GB4FUN
On the basis of value for money, I would go for Rapid's board Protobloc 1. Sometimes its positive and negative rails (horizontal connections across top & bottom of the board) are useful. But do keep an eye on them during lessons: the sticky black foam which keeps the contacts in place is vulnerable to vandalism.
It is much cheaper to get a reel of 0.6 mm connecting wire than to buy ready-made connector links. Students can prepare their own connectors, and at the end of a lesson you simply throw away any that are too short to recycle.
Activity AA5.12 'Building a baby monitor'
Connecting the circuit as shown in the textbook (pages 48 & 49) just makes it oscillate, causing the speaker to buzz. The technician in a C21 school has found a solution to this problem - connect an additional 100 microfarad capacitor between pin 6 and ground.
Pin numbers: A semi-circular indent in the surface at one end of the chip indicates where to find pin 1 (see diagram at the bottom of textbook page 48). Follow round anti-clockwise until you reach the pin number you want. 'Ground' is another word for the 0 volt side of power supply.
Do not replace the 6V battery with a low voltage power pack. School power packs generally produce a pulsed DC output, giving a 100 Hz ripple on the supply rails.
AA5.16 'A short history of pictures: small AC motor'
A low-voltage AC motor (1.5-3V) does not seem to be available commercially. We suggest that you make up an AC motor, using a Westminster kit, with a picture on each side of the armature. For further information see Practical Physics website. The AC version of this motor has a commutator at each end, in continuous contact with the power supply.
AA5.18 'Radio links'
It is no longer legal to transmit at 1 GHz, even with a very weak signal. You can make up your own wave kit using the 433 MHz kit available from Rapid.
AA5.19 'Tuning in: Integrated circuit M484'
For the kit needed for this see Rapidonline
AA5.26 'Signal conversion with PICs'
For the PICAXE interface board, software and battery pack – see the PICAXE-08 Starter Pack at Rev-ed
Activity AA5.27 'Serial transfer with PICs'
Three issues have been reported.
1 There are two typos in the PIC program instructions.
Activity 1 - In step a, the 3rd line of program should read:
serout 0, T300,(b0) (with a space between 'serout' and digit 0).
Activity 2 - In step i, the 2nd line of the program should read:
a1: serin 3,T300,b0 (with a space between ‘serin’ and 3).
2 The circuit diagram for Activity 1 is correct, but a connection shown on the prototype board is wrong. Connect A to pin 6 of the chip (not pin 5). Otherwise pin 5 is left floating so that its state is erratic. You may also find it helps to connect pin 2 of the chip to O V.
3 Seeing the PIC signal on an oscilloscope: Every 50 ms the PIC sends out a series of 9 bits, starting with a 0, which last for 30 ms. If the timebase is set at 10 ms/division, and the oscilloscope set to trigger on a falling edge, the patterns of 1s and 0s should fit into the left-hand part of the screen. But it all depends on how many divisions the oscilloscope has across its screen. If your students don't get a static image which they can view, try different timebase settings.
A6 Materials and performance
Activity AA6.7 'Cycling helmets'
For demonstration 2, make a switch with a sandwich-like structure: the ‘filling’ is a non-conducting mesh, with small openings (e.g. a 10 cm x 10 cm square from a string vest). The ‘bread’ is two pieces of aluminium foil cut 9 cm x 9 cm, that is, slightly smaller than the string vest square. At this point the sandwich analogy breaks down!
When a mass falls onto this make-shift switch (the ‘sandwich’), the two sheets of foil will temporarily make contact with each other through the string vest.
The mass and height it falls from should be such that the force of impact causes the foil to make contact, but not so large that the foil continues to make contact after the mass comes to rest.
Use this switch with a timer which can be set to run when a circuit between its two terminals is complete, and to stop when continuity is broken. A suitable arrangement will enable you to measure impact times.
AA6.13 'Thermal conductance of different fabrics'
The temperature probes will need to be flat to ensure they don't hold the plates and samples apart. Use a bare wire 'bead' thermocouple rather than one built into a probe.
It is not necessary to glue the items in place, because the glue may provide insulation and distort the results. Simply clamp the 'sandwich' together.
For the heating element: you could use any of the following:
- a cup warmer/heater designed to run off a car 12V supply
- a lab hot plate as used for heating beakers with stirrers (uses mains electricity, but designed for laboratory conditions, and some come with a thermostat)
- the cheapest option would be a home-made heating element. The output from a 1-metre length of 24 swg nichrome wire will be about 36 watts when connected to a 12 V supply. Wind the wire around a piece of strip-board. Remove the copper strips from the strip-board if necessary - these may short-circuit the heating circuit. See photos at the bottom of this web page.
Thank you to John Ellis (CLEAPSS) for the first two ideas, and Tim Henderson (Heston Community School) for the home-made version.
At the bottom of this page are Tim Henderson's photos of his kit.
Here is Tim Henderson's graph of results (64 KB)
AA6.19 'The roadie has a problem'
Preparing the multi-core cables Use Cat 5e standard network cable. Designed for computer local area networks, each of the strand pairs is colour coded and has the great advantage of being a solid copper conductor rather than strands. Gently score the insulating sheath at some point along the cable length. Bend and pull the sheath apart to expose one or two inner strands, at random. Snip the exposed copper wire with scissors. Push the sheath together to cover the gap and then use heat-shrink over the top to cover it. Although the area of damage will be visible, students cannot see which conducting path has been damaged.
With thanks to Tim Henderson, Heston Community School.
AA6.24 'Reflect or absorb?'
The length of drainpipe is not critical. Anything in the range 10 - 20 cm is long enough to make a reasonable thickness of the sample material.
A speaker works perfectly well as a detector in this application. We suggest 4 ohm speakers with diameter about 60 mm.
Using an empty carrier as a control: the empty sample carrier also reveals something about the detection system itself (e.g. sound carried by the pipe). The air too has an effect, and the result would be different if you were able to evacuate the pipe.
We are grateful to John Hawcock of Acland Burghley School, Camden for his suggestions.
AA 6.24 Reflect or absorb? photo Ailwyn Holmes
AA6.24 Reflect or absorb? signal photo Ailwyn Holmes
AA6.13 Thermal conductance of different fabrics: home-made kit by Tim Henderson of Heston Community School
To access CLEAPSS leaflet PS67 Practical Activities in the New Science GCSEs
Go to the CLEAPSS members' area on the CLEAPSS website. The username and password you will need is on your CLEAPSS Science Publications CD-ROM.
If you discover any difficulties not mentioned by CLEAPSS, please contact Emma Palmer who will either resolve the issue or forward it to CLEAPSS.