Reaction Time Tester




A month ago I knew nothing about Arduino and first project!
Looking back, this project combines allmost all of the tutorials that I have read in this short period: blinking LED, push button, piezo and LCD display. A useful project for every beginner!

I have made this device for some of my friends who have a hard time admitting how fast alcohol influences their driving abilities.
It will test you on three levels because they all have to do with driving a car safely:
  • DECISION time. 
  • REACTION time
  • Resistance to DISTRACTION.
The test starts as soon as you hold down the push button. When a red light appears, you should let go off the push button as soon as possible. Your reaction time will appear on the screen.
However, driving has to do with making fast decisions as well. So in random order you can get a green or blue light first (or multiples). You should not react to this and hold down the push button until the red light appears.
Finally, on occasions you will hear a short beep in between lights (just for fun). By now you are so tense to do well, that a simple distraction like a beep can and WILL set you off!! 

A fun game with your dinner guests upon arrival and confronting upon leaving!

Step 1: What You Need

  1. Arduino microcontroller (I have used an Uno).
  2. 1 RGB LED (you can use 3 separate ones if you like).
  3. 4 resistors (220 ohm).
  4. LCD Display
  5. Piezo speaker
  6. Breadboard.
  7. Push button.
  8. Wires.
  9. Ping pong ball (optional).
  10. Box.

Step 2: The Hardware.

For the experienced Arduino user this total view makes immediate sense. However, if you're a beginner just like me, a breakdown in steps can be useful.

Drawings were made with software by "Fritzing" (

I have used a RGB Led with a common Anode (3 Cathodes: R, G, B). Therefore the setup may seem a bit ackward. The consequence is that in the sketch (step 3): HIGH=off and LOW=on.

Step 3: The Sketch.

As bescribed in the Intro, different lights might appear in random order prior to the red light.
To make the test even more unpredictable, I have added two other features:
  1. The duration of a light is random (within some limits).
  2. The pause between lights is random as well (within some limits).
This is to avoid that people get a feel of the "rhythm" of the test. Making it predictable.
You can make the test harder by increasing these intervals. The sketch is in the TEXT file below.

Step 4: The Box.

This is quite straight forward and I never intended to copy the Instructables Robot, but once I was started, I saw some similarities...

Picture 1: Drill the pattern in the bottom of the box (to hold the Arduino in place). Hole size 3 mm.

Picture 2: Drill and cut two holes in the side for the USB connection and power supply (if you do not need to program the controller anymore and you have chosen to use batteries, you don't need this step. The Arduino is kept in place with small bolts (remove it prior to painting!).

Picture 3: Cut a slot in the lit of the box for the LCD. Drill another two holes, one for the LED (ping pong ball) and another one for the push button. Make sure that the hole for the ping pong ball has a sloping face.

Picture 4: Take two caps of a Coke bottle and cut the top section of the bottle as well. Glue the bottle top sections to the side of the box (make sure you have a nice and flat face for the glue).
Sand the box with a fine sand paper.

Picture 5: Apply several layers of paint (without the Coke caps).

Picture 6, 7, 8: install the Arduino. I have used a small breadboard for the components (Piezo and Pot. meter of the LCD). The LED was solderd seperately. Since the Arduino is tightly bolted into place, foam blocks can be installed against it and thus providing a tight fit for the LCD.
I didn't have red, blue and black wires so I used purple, green and grey:

Purple: +
Green: pin
Grey: Gnd 

2 People Made This Project!


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65 Discussions


2 years ago

Hello. I'm making a reaction timer for my biology project, and the design is inspired by your project. I want to be able to time and compare the reaction time between an LED and a sound. I was wondering if you could give me some tips on how to do that because I have never worked with kind of thing before. Thanks

4 replies

Reply 2 years ago

I'm not sure if I understand your question. The reason why there are different lights and beeps is to "throw you off" so you need to watch and listen carefully before releasing the button. Measuring the time between a LED an beep has nothing to do with your reaction time.


Reply 2 years ago

Sorry for the confusion. I know that the sound in your project was used to through people off, but i was wondering if there was a way in which I can program it to make sound and change color at different times in order to log the reaction time to those two variables separately. So, I can test whether or not people react faster to a visual or a sound.
If you don't get what im asking its alright. Like i said I'm new at this stuff, but thank you for replying. I appreciate it.


Reply 2 years ago

yes you can, but it requires some slight adaption to the program. In fact you could make two programs and load either one of them into the Arduino without telling the participant. You'll need to register the reaction times depending on the program you use.


Reply 2 years ago

*"throw people off"


3 years ago

Really liked this instructable. I was looking for a reaction tester that I could use for a geocache puzzle and this one fit the bill. I modified the code so once a finder logged a reaction time less than 400 milliseconds, a servo opens a compartment to reveal the treasure and log inside. Works great!

1 reply

Reply 3 years ago

Thanks and what a nice idea about locking!
Post an Instructable about it and I'll send you a patch. (help me remind though).


4 years ago on Introduction

Any updates on the programming? I seem to get into a long loop during a blue or green light press. It sometimes just goes blank, instead of displaying the 'too early'.

1 reply

5 years ago on Introduction

Awesome man! My grandpa made on of these when I was 6 or 7 and I would play with it for hours.


5 years ago on Introduction

hello. im interested in your project. do you have the schematic diagram for this? thanks in advance.

1 reply

7 years ago on Step 2

hiya pal!! really like the look of this as my uni project! if possible do you have a schematic diagram available??

1 reply

7 years ago on Introduction

Hi there. This project looks like an amazing beginning to my work with Arduino (it came in on Monday via mail, and I just bought the USB A to B cable today). There is only one problem - I cannot obtain an LCD Display for some time because all of my local stores are out of stock. Any possible substitutions?

One of my ideas would be to rewrite the code (I know the basics of the code) to round everything to the nearest thousandth (reaction time), and then have it go to a corresponding LED.

1 reply

Sorry for the late reply (holidays). have you tried getting a Display through internet. Shouldn't be too difficult.
You suggestion of rounding off will work. However, you need to really think about how to use the LED, maybe in patterns or even Roman numbers. Otherwise you'll need lots of them!