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Building a time tracker using arduino and blockchain tangletime part 2

Hello, This is part 2 of my project tangletime aka “Building a time tracker using arduino and blockchain”. Where I take you along my project to build an IOT time tracker using arduino and the IOTA blockchain. If you haven’t, please consider reading the first part .

Now that the plan is laid out. It’s time to plan for the hardware. We need those components :

An arduino board, a bluetooth module, a gyroscope and lots of cables and resistors to combine all of that together.

For the arduino board, cables and resistors I bought the Freenove RFID Starter Kit V2.0 with UNO R3. It’s an awesome starter kit with basically everything you need. Then for the Bluetooth module I bought the HC 05 and the gyroscope is the MPU 6050. ultimately with a more mature product, I think I’ll go for a beetle BLE, as it’s super small, cheap and handles Bluetooth out of the box. But that’s for a later stage.

I want to make as little calculations on the board as possible to lower the power usage and to make it easier to code. The idea is simple : connect the board to the gyroscope and whenever we detect a new stable orientation. Send that orientation to via the Bluetooth module to a connected phone.

The Bluetooth module with arduino

My HC-05 was not easy to tame, I found lots of tutorials online, most of them contradicting themselves on how to wire it. The main takeaway was that if you wire it to the 0/1 port, you need to unplug those before uploading your schematics to the board.

To test things out without using the gyroscope, I quickly plugged the infrared sensor included with the freenove kit, the part name is 1838B. I like it because it’s super easy to plug (it’s like 4 jumper cables). I could go with reading serial from my computer but I figured it would be nicer this way.

Arduino schematic for the bluetooth and IR module.
The Bluetooth module and IR module connection

I’m sorry for the clarity of the image, but everything is there I promise.

As for the code it was pretty straightforward :

    IR remote keypad
   0 : FF6897
   1 : FF18E7
   2 : FF6897
   3 : FF7A85
   4 : FF10EF
   5 : FF38C7
   6 : FF5AA5


#include <IRremote.h>
#include <SoftwareSerial.h>
SoftwareSerial EEBlue(10, 11); // RX | TX

int RECV_PIN = 12;        // Infrared receiving pin
IRrecv irrecv(RECV_PIN); // Create a class object used to receive class
decode_results results; // Create a decoding results class object

void setup()
  Serial.begin(9600); // Initialize the serial port and set the baud rate to 9600
  Serial.println("UNO is ready!");  // Print the string "UNO is ready!"
  irrecv.enableIRIn(); // Start the receiver

char value_to_char(unsigned long val)
  if (val == 16738455)
    return '0';
  else if (val == 16724175)
    return '1';
  else if (val == 16718055)
    return '2';
  else if (val == 16743045)
    return '3';
  else if (val == 16716015)
    return '4';
  else if (val == 16726215)
    return '5';
  else if (val == 16734885)
    return '6';
  else if (val == 4294967295)
    return 'X';
    return '?';


void loop() {

// if we recieve an IR message, send it via the bluetooth module.
  if (irrecv.decode(&results)) {
    // Waiting for decoding
    Serial.println(results.value); // Print out the decoded results 
    Serial.println(value_to_char(results.value)); // Print out the corresponding character


    irrecv.resume(); // Receive the next value

  // Feed any data from bluetooth to Terminal.
  if (EEBlue.available())

  // Feed all data from termial to bluetooth
  if (Serial.available())



To test everything, I used an app called “Bluetooth terminal HC-05” which basically allows you to send and receive data from the HC-05. It’s a lifesaver when you are working on the hardware side and don’t want to spend time making a quick and dirty app just to receive Bluetooth data.

Screenshot of the mobile app recieving bluetooth data
It works !

The final arduino setup

I wrote a whole article on the subject that you can find here ! So I’ll skip the details on how to set it up. And go straight to how I use it.

So here’s the “final” setup in terms of hardware. As for the code now all that’s left to do is to find all the x/y/z values for each side of the cube. But I don’t have a cube yet, and the arduino UNO board is way too big. So for now I’m going to make a first proof of concept where the time tracker only has two sides : register if the board is pointing left or right.

So after a few tests I realize that getting consistent reading is not as easy as I thought it would, there is a non negligible drift on the z value. There is probably some fine tuning necessary in the future in terms of which value = which side. but for now I only care about the x value since I want to know if the board is pointing left (x ~= -80) or right (x ~= 80)

Which translates to this code :

#include <SoftwareSerial.h>
#include <MPU6050_tockn.h>
#include <Wire.h>
MPU6050 mpu6050(Wire);
SoftwareSerial EEBlue(10, 11); // RX | TX
int pos = 0; // unset = 0, left = 1, right = 2 

void setup()
  Serial.begin(9600); // Initialize the serial port and set the baud rate to 9600
  Serial.println("UNO is ready!");  // Print the string "UNO is ready!"
  // offsets that I previously calculated using mpu6050.calcGyroOffsets(true);
  mpu6050.setGyroOffsets(-1.58, 0.69, -1.71);

void loop() {

  float x = mpu6050.getAngleX();
  float y = mpu6050.getAngleY();
  if (x < -50)
    if (pos <= 1)
      pos = 2;
  else if (x > 50)
    if (pos == 0 || pos == 2)
      pos = 1;



Pretty easy right ? Here’s a little demo of the whole system :

Data is sent to the phone via Bluetooth
if that video didn’t work try this link

So now we have a system that can send data to a paired phone and detect orientation ! success ! Now all that’s left to do is to port that code to a production board, 3d print a cube, fit all of that inside, get the position data for each side (side 1 is x/y, side 2 is x1,y1 etc…) And we are good to go on the hardware side !

If you have experienced drift issues with the MPU6050 and know a good fix. I would be interested. Please consider subscribing to the mailing list to avoid missing any future episode of this serie 🙂

Published inarduinocode