The Anatomy of a Fitness Tracker

Introduction

In this blog post, I will explain how simple it is to actually build a fitness tracker and customize it to fit your needs.

Companies like Fitbit, Amazfit and many others are competing to bring the best possible new fitness tracker.

The bottom line is simple, bring more battery life and sensors and win more market share.

What are the main components of a fitness tracker

A fitness tracker is typically composed of the following components:

1. IMU. Composed of an Accelerometer with a Gyroscope, the IMU is responsible for getting all of the amazing functionalities, your hand position, whether you are writing 0 or 1 [1], the number of your steps and fall detection, your activity type and so much more.

2. Medical Sensors. This is typically going to be the heart beat, and oximeter for blood oxygen level.

3. Time. It is a stable time source with an independent power source to keep precise time.

4. GPS. An ultra low power GPS receiver.

5. Power unit. It contains a battery charger, stable power source from USB, and it is used to cut power on component when they are not in use.

6. UI. A screen or a light indicator to inform the user.

7. WiFi / BLE. Used for data upload, receive phone notifications and updates.

8. Memory. An internal memory used to cache data before they are uploaded to the server, the memory can also be used to stock music on it.

9. NFC Payment. To pay using the fitness tracker.

10. Other sensors. A cocktail of other sensors including input buttons, pressure sensor, etc.

Here is a simple comparison of some of the main features provided by two different fitness trackers:

As you can see, it is not very simple to compare two different devices, but it should at least give you a glimpse of what it is capable of.

State of the art of the component

The most tricky part is first to find a micro-controller, that is :

• Small, 7x7mm down to 5x5mm.

• Minimal current consumption :

  • Sleep current : 8uA down to 1uA.
  • Working current : 10mA down to 28uA per Mhz.

• BLE current :

  • On receive (passive): 10uA.
  • On receive (active): 4mA.
  • On send (active): 5mA.

• WiFi current.

To be continued