What it shows
A bent bare wire and a wand loop form a switch that closes whenever your hand shakes and the loop touches the wire. The buzzer and LED make the contact obvious, turning a simple circuit into a game.
The science
The bare track wire is connected to the battery positive. The wand loop is connected, through the buzzer and the LED branch, back to the battery negative. While the loop surrounds the track without touching it, the circuit is open. Any touch closes it and current flows through the buzzer and through the LED with its 470 Ω resistor. A good player moves slowly because small, steady movements keep the gap between loop and track constant.
Materials
Cost: under Rs 100. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- About 60 cm of thick bare copper wire or a straightened coat hanger
- A 15 cm stiff wire bent into a small loop on the end of a pen as the wand
- An active buzzer rated 3 to 12 V
- One red LED and a 470 Ω resistor
- A 9 V battery with a snap connector
- A shoe box lid or wooden board as the base
- Insulated wire, tape and two small blocks to hold the track up
Safety
For this project: Wire ends are sharp; an adult should bend and tape them. Battery power only.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Bend the thick wire into a wavy path with two or three bends and push its ends into the blocks on the base.
Bend the thin wire into a 2 cm loop at one end and tape the other end along a pen to make the wand.
Before closing the loop, thread it around the track so the track passes through it.
Connect the battery red wire to one end of the track wire with tape and a bare wire end.
Connect the wand wire to the buzzer red lead and also to the 470 Ω resistor; the resistor goes to the LED long leg.
Join the buzzer black lead and the LED short leg together and to the battery black wire.
Touch the loop to the track: buzzer and LED both respond. Now try to go from one end to the other without touching.
Count the touches for each player and give three tries; the lowest score wins.
What you should see
Any contact between the loop and the track sounds the buzzer and lights the LED, so players can be fairly scored.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where is the switch in this circuit?
The wand loop and the track wire together form the switch.
2Why are the buzzer and the LED in parallel, not series?
So each gets the full 9 V; in series the buzzer would take most of the voltage and the LED might not light.
3Why does the track wire need to be bare?
The insulation would stop the loop making electrical contact.
4What limits the current when the loop touches?
The buzzer’s own resistance and the 470 Ω resistor in the LED branch.
Take it further
Add a 555 timer that keeps the buzzer sounding for two seconds after a touch so brief touches cannot be hidden.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Robotics
Electronic Components Handbook
Resistors, capacitors, LEDs, diodes, transistors and more, with how to use each
Science projects
Best Out of Waste Science Projects
Working models from bottles, cardboard, CDs and old parts