Picture of Arduino Bike Speedometer
IMG_9279 copy.jpg
Monitor your road speed using the Arduino. This project uses a magnetic switch (also called a reed switch) to measure the speed of one of the bike's wheels.  The Arduino calculates the mph, and send this information out to the LCD screen on the handlebars as you ride.  It is compatible with any kind of bike/wheel, simply enter the radius of the wheel in the firmware to calibrate the device for your setup.

Parts List:

(1x) Arduino Uno REV 3 Radioshack 276-128
(1x) Switch-Magnetic Reed Radioshack 55050593
(1x) 10K Ohm 1/4-Watt Carbon Film Resistor Radioshack #271-1335
(1x) 9V Alkaline Battery Radioshack #23-866
(1x) Heavy-Duty 9V Snap Connectors Radioshack #270-324
(1x) PC Board with Copper Radioshack #276-147
(1x) Parallax 27977-RT Serial Backlit LCD Radioshack 276-120
(x2) SPST PC-Mountable Submini Toggle Switch Radioshack #275-645
(2x) Male Header Pins Jameco 103393
(1x) Female Pin Sockets Jameco 308567

Additional Materials:
22 Gauge Wire Radioshack #278-1224
Solder Radioshack #64-013
sand paper
wood glue
hot glue
zip ties

Download Arduino IDE

Step 1: Schematic

Picture of Schematic
The schematic for this project is shown above.

It consists of three switches:
-one to connect to a 9V power supply
-one to switch the backlight of the LCD on and off
-a magnetic switch (called a reed switch) which closes each time the wheel completes one full rotation.

The Parallex LCD is designed to connect to the arduino using only three pins (ignore the labels and the other pins int his schematic).  One to 5V, one to ground, and a third to serial out (TX)- on the arduino, serial out is digital pin 1.

10kOhm resistors are connected to the reed and backlight switches to prevent excess current between 5V and ground (you should never directly connect 5V and ground on the arduino!)
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b3nz11 year ago

I've tried using this code to measure windspeed on an anemometer for a project of mine. it's a rotating magnet and a reed switch so it's the same principle. The reed test works fine. i've changed the radius (0.87 inches) to fit with my windspeed sensor. However when i upload the code, the serial port view just gives me 0's for MPH for the first reading then a steady steam of 28.21 MPH. Any ideas?

Did you manage to work this out in the end b3nz1? I'm doing similar.

ikowalska6 months ago

Hi Amanda, I have a problem with your's code on my stationary bike. Speed calculated by arduino is very low (sth like 1 - 5 km/h max) and I don't know what is wrong :/ I changed only radius for 0.12 m (this is radius of my stationary bike wheel). Is that any problem with fact then my bike have a belt drive ? Something like this electronics.stackexchange.com/questions/140063/measure-the-speed-of-a-stationary-bike-with-belt-drive ? Please help!

A little late, but FYI the wheel size should be in Inches not meters

mholthaus992 months ago

Hi Amanda

Great instructable! I'm trying to use the same principles in a slightly different project in which I am importing a library what already uses the Timer1 interrupt - what would be the implications of using Timer 2 as the interrupt in the code to measure the speed of the wheel in terms of accuracy of measurement? And is it simply a case of amending the timer setup to use TCCR2A etc.?

ŽanP5 months ago


Can anyone share code for this but with classic display? I dont have experience with programming so i need some help. Thanks for helping.

juan.proano17 months ago


huzy12310 months ago


which other lcd is available to use?

iNishantSingh10 months ago

I have a similar code. Initially, I was using the capacitive sensor technique but I realized that it is severely affected by external conditions. I am thinking of using the reed switch. For measuring distances, has anyone faced problems with the reed switch method ?

iNishantSingh10 months ago

I have a similar code. Initially, I was using the capacitive sensor technique but I realized that it is severely affected by external conditions. I am thinking of using the reed switch. For measuring distances, has anyone faced problems with the reed switch method ?

iNishantSingh10 months ago

I have a similar code. Initially, I was using the capacitive sensor technique but I realized that it is severely affected by external conditions. I am thinking of using the reed switch. For measuring distances, has anyone faced problems with the reed switch method ?

saymowan11 months ago

hahaha amazing!! Thanks for sharing!

jorgito12311 months ago

What things should i change to use it in km/h? And whats that 56.8 in the code?

jeneral1 year ago

im using this LCD

is there anything i have to modify?
amandaghassaei (author)  jeneral1 year ago

this lcd does not support serial communication, you can get it to work, but you will have to read the datasheet and make some changes to the code.

Could you please help me with the code for this LCD display??? Please (Serial communication 16x2 display) Thank You

kgrr mendojoel11 months ago

See this article:

biinJC1 year ago

Hi. Can I still use the code for reed if I change the reed switch to hall effect sensor? Because my reed switch can't get accurate mph(double / triple of the actual speed) when the speed is slow

amandaghassaei (author)  biinJC1 year ago
but it does work when it's fast?

When it get faster, the reed switch works fine when the speed increase even the result i get doesn't show a linear increment when i increase the voltage by 0.5 each time (I am using a DVD player motor with disc taped on it to act as the bike tyre) and it break down after 47mph.

Murphy401 year ago

How would you change the final speed code to also display the distance travelled along with the speed?

achand81 year ago

I thought of the same thing. But I would have used a hall effect sensor and a standalone Atmega 8. Not everyone has an arduino for every project

M.Hawse1 year ago

Thank you so much for posting this project. I'm building something similar to this and I came across this project of yours while looking for some additional ideas. It provided a lot of much needed inspiration. Best wishes to you...

satrio1 year ago

Amazing! sorry I curious, may I get a picture of proteus simulation
project? I really want to know how it does work very nice. Thanks in

BrianRico1 year ago

Your design will help out tremendously. Our design includes controls for a flywheel that will help stabilize a bicycle at slow velocities, and it is extremely important to get a very accurate forward velocity of the bike at slow velocities. Instead of using one magnet, my idea is to use multiple magnets equally spaced around the tire to get a more accurate angular velocity of the wheel. I would like to first ask for your help on modifying your code to include reading multiple magnets with one switch. Help modifying your code at all will be greatly appreciated. Love the instructable.

amandaghassaei (author)  BrianRico1 year ago
if your magnates are spaced evenly around the wheel then you'll just need to divide the speed calculation by the number of magnets to get the right speed for your setup. Sounds cool, post a pic when you're done!
pzedzik1 year ago


I was just wondering about the code for radius. Would it not be better to put in the radius on the wheel of where the reed switch is, vs. just the radius of the wheel? That way the speed is much more accurate?

***like where the magnet on the wheel is? (I'm using a hall effect sensor for my project)***

amandaghassaei (author)  pzedzik1 year ago

the reed switch is used to measure rpm, so it doesn't matter where it is on the wheel when we measure it. The radius of the wheel is used to calculate the distance the bike travels per rotation.

Miss I have a problem with your project when I compile I get the first line goes to zero in the other 47.68 without placing the magnet I can failicar the correct scheme reed switch assembly
amandaghassaei (author)  mblanco rios1 year ago

does it work after you spin the wheel?

Awesome instructable. I am working on a similar speedometer for my motorcycle. I was wondering, which would be better to use, a magnetic reed switch like you did or a hall effect sensor. I have a feeling that the reed switch might not be fast enough to sense the front wheel spinning at 60 - 70 MPH. Any suggestions?
amandaghassaei (author)  AgnostosTimos1 year ago
I think the hall effect sensor will be better, the reed switch is mechanical and will eventually break down.
yoopee1 year ago
I have the same problem. It also shows 56.84 when bike goes very slow.
Anyone can help with code? Amanda? :-)
iuriandrion2 years ago
Hello! Nice job you made. I tried to make this at home. i used the code without the lcd, and the values i sent to the serial monitor. It worked but i had a problem... When the reed is right in front of the magnet, the same number (56.84) appears at the monitor, while the reed is in front. Do you know what is happening?
One more thing. In this code, how can I make and send to the monitor an avarege speed of the bike? Can you help me?


jcservek2 years ago
I'm attempting to run this project without the display, only utilizing the reed switch which I harvested from an old bike computer to begin with. Unfortunately, when I check the serial monitor after uploading the sketch that is supposed to output mph, I get one or two 0.0mph readings, and then a continuous string of 45.91. If I put the magnet to the switch, it will drop back to 0.0, but only stay there so long as the magnet is continuously activating the switch. Does anyone have any ideas as to what might be causing this behavior?
amandaghassaei (author)  jcservek2 years ago
cool, I think some of the lcd specific commands were getting in the way, try this:

//outputs speed of bicycle to LCD

//tire radius ~ 13.5 inches
//circumference = pi*2*r =~85 inches
//max speed of 35mph =~ 616inches/second
//max rps =~7.25

#define reed A0//pin connected to read switch

//storage variables
float radius = 13.5;// tire radius (in inches)- CHANGE THIS FOR YOUR OWN BIKE

int reedVal;
long timer = 0;// time between one full rotation (in ms)
float mph = 0.00;
float circumference;
boolean backlight;

int maxReedCounter = 100;//min time (in ms) of one rotation (for debouncing)
int reedCounter;

void setup(){

reedCounter = maxReedCounter;
circumference = 2*3.14*radius;
pinMode(2,OUTPUT);//backlight switch
pinMode(reed, INPUT);

// TIMER SETUP- the timer interrupt allows preceise timed measurements of the reed switch
//for mor info about configuration of arduino timers see http://arduino.cc/playground/Code/Timer1
cli();//stop interrupts

//set timer1 interrupt at 1kHz
TCCR1A = 0;// set entire TCCR1A register to 0
TCCR1B = 0;// same for TCCR1B
TCNT1 = 0;
// set timer count for 1khz increments
OCR1A = 1999;// = (1/1000) / ((1/(16*10^6))*8) - 1
// turn on CTC mode
TCCR1B |= (1 << WGM12);
// Set CS11 bit for 8 prescaler
TCCR1B |= (1 << CS11);
// enable timer compare interrupt
TIMSK1 |= (1 << OCIE1A);

sei();//allow interrupts


ISR(TIMER1_COMPA_vect) {//Interrupt at freq of 1kHz to measure reed switch
reedVal = digitalRead(reed);//get val of A0
if (reedVal){//if reed switch is closed
if (reedCounter == 0){//min time between pulses has passed
mph = (56.8*float(circumference))/float(timer);//calculate miles per hour
timer = 0;//reset timer
reedCounter = maxReedCounter;//reset reedCounter
if (reedCounter > 0){//don't let reedCounter go negative
reedCounter -= 1;//decrement reedCounter
else{//if reed switch is open
if (reedCounter > 0){//don't let reedCounter go negative
reedCounter -= 1;//decrement reedCounter
if (timer > 2000){
mph = 0;//if no new pulses from reed switch- tire is still, set mph to 0
timer += 1;//increment timer

void displayMPH(){
Serial.print("Speed = ");
Serial.println(" MPH ");

void loop(){
//print mph once a second

Hey, nice project, but isn't it a little big?! :)
I know it's not so easy to keep things small, but i would suggest using an Arduino Nano or similar, and a smaller 3D Printed box...
And regarding the electronics of it, maybe use a dynamo and a rechargeable battery?
The older dynamo were pretty annoying, but i think the newer ones are pretty awesome, since they're so silent and have a bearly noticeable resistance (mechanical resistance) since they're in the center of the wheel.
Anyhow, nice project, i like these kinds of projects, because they're relatively easy to build and you can always improve them with fairly small efforts (eg. add average speed, driven distance, automatic standby when the wheel didn't turn for a certain amount of time, etc.), there are thousands of possibilities! :)
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