A VR Cycling Experience for $40

I’ve made an Arduino thing that can wirelessly talk to a mobile device over BLE and can now meter the revolutions of a wheel with an optical tachometer. I’m using these two hardware features to make a virtual reality (VR) cycling experience and I’ve got a working demo to share! Here’s how this works:

First, the Arduino thing is positioned to point at the back tires of a stationary bike. (I’m using a mountain bike on an indoor trainer but the beauty of this non-invasive approach is that you could use it with treadmills, ellipticals, rowing machines, or anything that has a looping/revolving surface.)


A strip of paper is taped to the tire. Each time the wheel makes a complete rotation, the Arduino will detect when the piece of paper passes by and then sends a wireless message to the mobile phone.

The mobile phone is placed in a viewer that is strapped to my face. (I used a $10 headset that more comfortably fits the iPhone 6S Plus, but any ol’ viewer will do.)

Screen Shot 2016-01-23 at 2.30.54 AM.png

In software, a virtual bike is created to travel in a virtual environment. The virtual bike will only nudge forward whenever the app receives a message from the Arduino reporting that the physical bike’s wheel has made a complete rotation. We are effectively mapping the physical action of pedaling to movement in the virtual space to make an oversized gaming controller.

Screen Shot 2016-01-23 at 1.23.26 AM.png

The virtual environment is constructed in Unity. To render for virtual reality, I’m using Google Cardboard  – a free software SDK for mobile VR. The SDK for Unity is drop dead simple – just drag and drop a prefab into your scene and you’ll instantly have a stereo camera rig to manipulate.

Screen Shot 2016-01-23 at 1.34.51 AM.png

This camera rig is set to move along a spline path whenever the app receives a BLE ping from the Arduino. That’s pretty much all it takes! So there you have it, a VR cycling experience for a whopping total of $40:

  • Arduino thing? $30.
  • Mobile VR headset? $10.
  • Software? Priceless.

Yes it’s DIY, but to put things in perspective, take a look at the current offerings on the market today:

  • Peloton: $2,000 bike with built in touchscreen monitor. No VR. Pedaling does not affect the video screensaver 😦
  • Virzoom: $300 bike ($600 Oculus + ~$2,000 PC not included)
  • Ciclotte: $10,700 bike?!

Screen Shot 2016-01-24 at 1.25.26 AM.png

This was a fun little personal project and I’ve learned what I set out to learn, so this is where I move on – but if you’re going to try something similar, here’s some things I’d consider in retrospect: It wouldn’t be too much of a stretch to have the physical bike steer the direction of the virtual bike. Why not give the player total freedom to explore? Also, does the virtual bike have to be a bike? I’ll just leave this right here: http://goo.gl/fRWY6Z.

For the interested Makers out there, below is a schematic of the IR sensor along with the Arduino code. Tinker away!


…and here’s my Arduino sketch:

#include SPI.h
#include "Adafruit_BLE_UART.h"

// nRF8001 pins: SCK:13, MISO:12, MOSI:11, REQ:10, ACI:X, RST:9, 3Vo:X
unsigned long time = 0l;
boolean connection = false;
uint8_t btm = 65;
uint8_t out = btm;
uint8_t cap = 90;
#define persec 30
#define sendat (1000/persec)

int irPin = 7;
int irSensorPin = 5;
int testLEDPin = 4;
int tripTime = 0;
int lastTrip = 0;
int tripBetween;
boolean detectState = false;
boolean lastDetectState = false;

void setup(void)

  pinMode(irPin, OUTPUT);
  pinMode(irSensorPin, INPUT);
  pinMode(testLEDPin, OUTPUT);

  uart.setDeviceName("YanBLE"); /* define BLE name: 7 characters max! */


void loop()
  pollIR(); // IR sensor
  uart.pollACI(); // BLE

void pollIR() {
  digitalWrite(irPin, HIGH);

  if (digitalRead(irSensorPin) == LOW) {
    detectState = true;
    if (detectState != lastDetectState) {
      // run the first time reflection is detected

      Serial.println("message sent via BLE");
      if (connection == true) {
        sendBlueMessage("1"); // dummy data passed here, this can be any value. We just need to ping the app
      lastDetectState = true;
    else {
      // here we are seeing the same reflection over several frames
      // turn test LED on to give visual indication of a positive reflection
      digitalWrite(testLEDPin, HIGH);
  else {
    detectState = false;
    lastDetectState = false;
    digitalWrite(testLEDPin, LOW);

  BLE-related functions below this point
void aciCallback(aci_evt_opcode_t event)
  // this function is called whenever select ACI events happen
  switch (event)
      Serial.println(F("Advertising started"));
      connection = true;
      connection = false;

void rxCallback(uint8_t *buffer, uint8_t len)
  // this function is called whenever data arrives on the RX channel

void sendBlueMessage(String message) {

  uint8_t sendbuffer[20];
  message.getBytes(sendbuffer, 20);
  char sendbuffersize = min(20, message.length());

  Serial.print(F("\n* Sending -> \"")); Serial.print((char *)sendbuffer); Serial.println("\"");

  // write the data
  uart.write(sendbuffer, sendbuffersize);


78 thoughts on “A VR Cycling Experience for $40

      1. I assume you used an Android device in the Google Cardboard, if so what app are you using? I think you built a custom app, if so would you share your app?

  1. Thank You so much on teaching us how it is done. Can you teach me how it works after the sensor gets reflection and measure the current speed? How did the sensor know I just stopped? Thank You in advance~

    1. In my implementation, the sensor doesn’t actually calculate speed (I started with that approach but didn’t end with it). All it does is ping the mobile device each time it detects a reflection. The virtual bike applies a force forward and it has its own decay in speed. The sensor knows nothing about the fact that I’ve stopped, it just fails to ping the mobile device more. Here’s some psuedo-code to give you a hint:

      Set IRLightPin to HIGH;
      if (IRSensorPin == LOW) {
      detectState = true;
      if (detectState != lastDetectState) {
      lastDetectState = true;
      else {
      detectState = false;
      lastDetectState = false;

  2. hey i tried your program but its telling that
    Arduino: 1.0.6 (Windows NT (unknown)), Board: “Arduino Uno”
    sketch_dec13a.ino:1:10: error: #include expects “FILENAME” or
    sketch_dec13a.ino:2:31: error: Adafruit_BLE_UART.h: No such file or directory
    sketch_dec13a:12: error: variable or field ‘aciCallback’ declared void
    sketch_dec13a:12: error: ‘aci_evt_opcode_t’ was not declared in this scope
    sketch_dec13a:8: error: ‘Adafruit_BLE_UART’ does not name a type
    sketch_dec13a.ino: In function ‘void setup()’:
    sketch_dec13a:34: error: ‘uart’ was not declared in this scope
    sketch_dec13a:37: error: ‘aciCallback’ was not declared in this scope
    sketch_dec13a.ino: In function ‘void loop()’:
    sketch_dec13a:44: error: ‘uart’ was not declared in this scope
    sketch_dec13a.ino: At global scope:
    sketch_dec13a:80: error: variable or field ‘aciCallback’ declared void
    sketch_dec13a:80: error: ‘aci_evt_opcode_t’ was not declared in this scope

    What should i do man?????

  3. Dear Paul,
    I am working with Prof. Steven LaValle to help obtain permissions for borrowing figures or pictures in his upcoming book Virtual Reality, to be published by Cambridge University Press. The book is online here:


    We are hoping to include the picture of yours (https://pauldyan.files.wordpress.com/2016/01/vrbikethumb.png?w=1200) in this book (Chapter 10, Figure 10.8b ). Could we please have your permission for this? Thank you.


    Adam Warkoczewski

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