Читать книгу The Dangerous Book for Boys - Conn Iggulden - Страница 24
ОглавлениеYou will need
An old alarm clock.
Bulb.
Two pieces of insulated electrical wire with bare copper ends.
Adhesive tape.
A battery – C or D size.
These are very simple to make – and deeply satisfying. For the timer, any wind-up alarm clock will do – preferably one with plastic hands. The idea is to use the clock to complete a circuit and turn on a light. You want the bulb to turn on in twenty minutes – to win a bet perhaps, or to frighten your little sister with the thought that a mad axe murderer is upstairs.
First, remove the plastic front of the clock. Tape wire to each hand, so that when one passes under the other, the bare ends will touch. It should be clear that a circuit can now be made with a time delay of however long it takes the minute hand to travel around and touch the hour hand.
Attach one of the wires to a positive battery terminal. Tape a torch bulb to the negative terminal and the end of the other wire to the end of the bulb. Test it a few times by touching the hands of the clock together. The bulb should light as the wires on the hands touch and complete the circuit.
Bear in mind that the hour hand will have moved by the time the minute hand comes round, so it’s worth timing how long it takes for the bulb to light after setting the minute hand to, say, fifteen minutes before the hour. You can then terrify your young sister with the tale of Hamish McGee, the butcher of Margate.
TRIPWIRE
This is almost the same thing, in that it uses a battery circuit with a bulb linked to a switch – in this case a tripwire. With a long enough wire, the bulb can be lit some way from the actual trip switch for longer warning times.
You will need
Clothes peg.
Wine cork.
Tin foil.
Fishing line or string.
Battery, bulb and insulated wire, as with the timer set-up.
Adhesive tape.
Wrap foil around the ends of the wooden or plastic clothes peg. Attach your wires with tape to those foil ends, running both to exactly the same battery and bulb set-up as the alarm-clock switch above.
The important thing is to have a non-conducting item between the jaws of the clothes peg. We found a wine cork worked quite well. The wire itself must also be strong enough to pull the cork out – if it snaps, the bulb won’t light. Fishing wire is perfect for this as it’s strong and not that easy to see. It is also important to secure the clothes peg under a weight of some kind. Only the cork should move when the wire is pulled.
When the cork is pulled out, the jaws of the peg snap shut, touching the foil ends together, completing the circuit and lighting the bulb to alert you.
This works especially well in long grass, but its main disadvantage is that whoever trips the switch tends to know it has happened. Enemy soldiers would be put on the alert, knowing they were in trouble. Of course, in a real conflict, the wire would have pulled out the pin to a grenade.
PRESSURE PLATE
One way of setting up a trip warning without the person realising is with a pressure plate. Again, this relies on a simple bulb circuit, but this time the wires go to two pieces of cardboard held apart by a piece of squashable foam such as you might find in children’s toy letters. A bit of sponge would also be perfect.
This time, tape foil squares over the bare ends of the wires on the inner surfaces of the cardboard and set up a simple bulb and battery circuit as before. With only light pressure from above, the two bits of cardboard come together, bringing the foil squares into contact. The circuit is made and the warning bulb comes on. Enjoy.
