What it shows
The time between a light and your button press is your reaction time, usually around 0.2 to 0.3 seconds. A microcontroller timer measures it to a thousandth of a second, so you can compare people and conditions.
The science
After a random wait of 2 to 6 seconds the green LED lights and the sketch stores micros(). When the button is pressed it subtracts the stored time to get the reaction time in milliseconds. If the button is pressed during the random wait, the red LED lights instead as a false start. Reaction time includes the time for the eye, brain and muscles to act, typically 200 to 300 ms for sight.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno or compatible board
- A green LED, a red LED and two 220 Ω resistors
- A big push button
- A 16 x 2 I2C LCD (or use the Serial Monitor)
- A breadboard and jumper wires
- A notebook for results
Safety
For this project: USB 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.
Connect the green LED to pin 4 and the red LED to pin 5, each with a 220 Ω resistor to GND.
Connect the button between pin 2 and GND using INPUT_PULLUP.
Connect the LCD to 5 V, GND, A4 and A5.
Write the sketch: on start, wait a random time of 2000 to 6000 ms using random().
While waiting, if the button reads LOW, flash the red LED and show FALSE START.
Otherwise turn on the green LED, store micros(), and wait for the button press.
Calculate the time, display it in milliseconds, and keep the best of five tries.
Test ten friends and write a table of averages for each person.
What you should see
The display shows reaction times, typically 200 to 350 milliseconds, and warns when someone presses too early.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is reaction time?
The time taken to respond after a stimulus.
2Why use a random delay?
Otherwise people could guess when the light comes on and press before it.
3What is a false start?
Pressing before the signal.
4Does sound or light give a faster response?
Sound is usually a little faster, about 170 ms against 190 ms, but test it yourself.
Take it further
Add a buzzer and compare light and sound reaction times for the same people.
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
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Viva Questions for Science Projects
How to answer examiner questions, with sample questions for popular projects