Designing SPECTRA
We hope you enjoyed defeating SPECTRA and also that you noticed some of the science and
engineering that was used in the tasks. All the activities were related to the Electromagnetic
spectrum and we had the whole spectrum covered except for X-rays and Gamma-rays.
Taken from: http://www.antonineeducation.co.uk/physics_gcse/Unit_1/Topic_5/topic_5_what_are_the_uses_and_ha.htm
Here are some hints about how we designed and made SPECTRA and it might give you some ideas if
you’d like to create your own super evil technical organisation.
Infra-Red: Seeing in the dark
The night vision camera we used was a wireless mini camera designed to go in bird boxes. This type
of camera uses an analogue microwave link to send the video to a receiver box. They’re often used
for home security. http://www.spycameracctv.com/spycamera/wireless-birdbox-day-nighthidden-camera-receiver
The camera sees in the dark by using Infra Red Light emitting diodes (around the lens) to light up the
dark room. Although Infra-Red is invisible to the human eye, most digital cameras can pick up near
Infra-Red (try pointing a TV remote control at your mobile phone camera and see what happens).
Near infra-red is energy that exists at frequencies just below the red part of the visible spectrum.
You may know that Infra-red is also heat energy. This is called far infra-red as it is far from the
visible spectrum. Far infra-red energy can be detected by thermal imaging cameras which are used
for finding holes in thermal insulation. This technology is very different to the cameras you used
today. http://missionscience.nasa.gov/ems/07_infraredwaves.html
Here the saucepan is hot, while
the bottle is full of cold water.
Microwaves:
The infra-red camera uses a wireless microwave link to send the video back to the monitor outside
the darkroom. Microwave communications is essentially the same as radio communications but at
a higher frequency (2.4GHz is often used). The camera can use one of 4 different channels without
needing a licence and this is useful to avoid interference with our other cameras and the other
exhibitors at the Big Bang fair. Interference occurs when two broadcasters send radio or microwave
signals at the same frequency and the receivers cannot separate the two signals. One of the
advantages of using microwaves is that the wavelength is much longer than the darkroom walls and
therefore the signal is able to pass through without being absorbed.
http://www.revisionworld.co.uk/node/8690
As a point of interest, the camera link uses 2.4GHz which is the same frequency used by a microwave
oven. Do you know why the camera didn’t cook your head?
Visible light:
Obviously you used visible light a lot today! For instance, you used it to communicate inside the
darkroom using an optical fibre link. The electro-optical transducer circuit (i.e. the circuit that turns
electronic currents to light) uses analogue intensity modulation. The circuit uses the electronic
signal from the microphone to control a light emitting diode so that a strong signal makes a bright
light and a weak signal produces a low light. The optical-electronic transducer at the other end of
the fibre does the reverse. It uses a photo-detector to turn the light levels back into the electronic
signal. This signal is amplified and used to drive a speaker inside the darkroom. You could make
your own circuits to do this, or you could cheat and buy a kit on the internet like we did
http://www.quasarelectronics.com/3026-fibre-optic-audio-link.htm. This kit is something you
could build at school or at home if you have soldering iron. It is fantastic way to see how well the
light gets down the fibre!
Optical fibres make great communication links because they can be very long without losing the
signal. A single fibre can carry a huge number of conversations without filling up (in engineering
terms optical fibres have a large channel capacity). Finally, they are small and light and can be bent
without affecting the signal quality. Finally, finally, they don’t suffer from interference like radio
waves do.
The fibre you used today was made of plastic, but the ones used for Broadband networks into your
house are made of glass. They work because light travels more slowly in glass or plastic than in air
and therefore light becomes trapped inside the fibre because of Total Internal Reflection:
http://www.youtube.com/watch?v=8VZHym6HqVU&feature=endscreen&NR=1
From http://www.oneschool.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/light/totalinternalrefraction
.html
Radio Waves:
Radio waves can be used for communications of course, but here you used them to control a car
with a camera on. Some people confuse radio control with infra-red control. The easy way to tell
them apart is to look on the remote control for an antenna (which is engineer talk for an aerial).
Also if you can control the car in another room, you are definitely using radio control, not infra-red.
Do you know why this is? We bought 3 cars for SPECTRA so we could keep the batteries charged.
One of them works in the High Frequency radio band at 27MHz, though we have to admit the other
cars actually work in the 2.4GHz microwave band. Apart from cheating and not using a real radio
wave frequency, this caused an interference problem with the wireless cameras that work at the
same band. The result was shaky pictures and cars! Fortunately the cars are designed to be used in
interfering environments with other cars present and when they are turned on they ‘look’ for an
unused frequency near 2.4GHz. Turning the camera on first solved the problem as the car would
then seek out a free channel.
Another issue we had was that all RC cars are made for racing and can go extremely fast. This was
not great for us as cars flying out the maze onto people’s heads could be funny, but not popular.
We considered several clever and complicated ways of adjusting the electronic velocity control
circuit – and eventually decided to stick a plate around the trigger to limit its movement. This did
the trick and is a good engineering principle – never go for a complicated solution when a simple one
will do!
We initially also planned to use radio waves in the darkroom having a radio mic to talk through the
walls. But we didn’t do this in case we interfered with one of the theatre shows at Big Bang which
could use a lot of radio mics. It wouldn’t be great for an audience of several hundred to listen to
one of our participants saying ‘left a bit, up a bit, keep still you twerp’…
http://www.howstuffworks.com/radio-spectrum.htm
Electronic Control System and Electro-Mechanical Actuators
Mechanical devices that are controlled by electric currents are known as actuators. These include
things like solenoids, relays, motors and valves. http://www.freestudy.co.uk/control/t2.pdf . We
used a whole load of these in the reward cabinet at the end of SPECTRA.
The electronics and actuators were controlled by a device called a Field Programmable Gate Array or
FPGA. http://www.youtube.com/watch?v=L2wsockKwPQ. These are used in loads of modern
electronic systems because they are so flexible. In the old days all electronic circuits had to be made
from scratch by soldering lots of components onto boards. But, an FPGA is a programmable circuit
– it is a chip stuffed full of tiny electronic components and even computer processors. These can be
connected together in different combinations by sending switching instructions into the chip - and a
really complicated circuit can be made in a really short time.
Our FPGA was programmed to follow the instructions in the flow chart below. See if you can work
out how it controlled SPECTRA for you.
Flow chart of control system
7 illuminated coloured buttons
Reset
7
Input correct
button
number
These 7 lines will need to be 2 or 3
metres long
Microprocessor or FPGA
7
Open valve to
cylinder to
arm airzooka
Open valve to
fire airzooka
Raise latch to
open reward
drawer
Open valve to
fire ping pong
ball
Amp &
speakers
7 bright
indicator lights
If you’ve got a good science or DT club at school they might have processor circuits such as PICAXE
or Arduino which you can programme to control electronics. If you’re really keen you can even get
them for home: http://www.picaxe.com/Project-Gallery and http://oomlout.co.uk/starter-kit-forarduino-ardx-p-183.html. They’re a great way to control some useful electronics without needing to
be a circuit designer and many hobbyists use them.
We controlled the ping pong ball cannon using an air line from a fridge compressor. The air line (or
hose) was connected to the cannon using an electrically controlled valve. We were able to make the
ball hover by sending lots of short bursts of air – then to fire it with a long burst of air.
The air zooka was air controlled too – we used a pneumatic cylinder (or piston) to draw back the
elastic. It was really difficult to think of a way to pull back the strong elastic and then release it quick
enough to get the air whoosh. You can see the way we did it through the window at the back of
the cabinet. Is this the best way – or could you think of a better way to fire an air zooka or ping pong
ball with electronic control?
Incidentally, we drew our logo on the ping pong balls using an Egg-bot which we built from a kit from
http://egg-bot.com/index.php?page=about. This was designed as part of a challenge to make a
machine to draw on an egg. These challenges can be great fun and are run by all sorts of
organisations such as RAE, lego league, etc http://www.youngeng.org/index.asp?page=54. Why
not get your Science/DT teachers to enter the school in some – they’re a great training ground for
our future engineers.
If you are going to design and build electronic and engineering projects at home, then a great
website is mindsets. http://www.mindsetsonline.co.uk/. They’ve got all sorts of interesting stuff
and they’ll sell you small amounts if you just want to find out what things do.