• Subir Biswas

Inside of a Smartwatch | Tech-Knowledge

Smartwatches replaced almost all the regular watches (except a few high end swiss watches).


Because of additional features and of course the health monitoring. And as manufacturers are providing a magnificent application to use those raw health data from the smartwatches which provides a historical value to the user and identifies the changes happening everyday and triggers if there is an issue. But for doing so a complex electronics circuit is working in the background.

Everybody might not be interested in this but this might be helpful for those who want to understand how this is happening in the background. Mostly the students and those who want to develop something similar will get some idea from here.

Recently E&T magazine published a teardown of an OnePlus smartwatch. It is a very interesting topic to get a smartwatch inside. For this article I’ll be using the reference photos from OnePlus smartwatch. However, the basic architecture is very common and followed by most of the manufacturers. Let’s start..

The Evolution of Smartwatch

Making or arranging the components in the round pcb (Printed Circuit Board) is a bit tricky compared to the square one. You know the simple mathematics about the area calculation for a square and circle.

Followings are are basic external parts anyone can see inside a smartwatch:

  • Display

  • Speaker

  • Battery

  • Motherboard

  • Body / Bezel

  • Sensors

However, if you want to go a bit inside two, most parts are the Motherboard and sensor board. I have tried to name a few main components in this blog and the working principle of few sensors. Component details of the motherboard depend on requirements and features.

Here is few main component details from the Motherboard:

  • Bluetooth SoC

  • Battery charger SoC

  • Accelerometer

  • Gyroscope

  • Audio Codec

  • Audio Amplifier

  • Memory

  • Microcontrollers

  • Location Controller

An invention Wearable tracking with positioning accuracy from u‑blox

Here is few main component details from the sensor board:

  • Pulse sensor

  • Oxygen saturation sensor

  • Temperature sensor

  • Blood sugar sensor

  • ECG sensor

Working Principle of a Pulse Sensor

A pulse wave is a change in the volume of a blood vessel that occurs when the heart pumps blood, and a detector that monitors this volume change is called a pulse sensor. Pulse sensors in smart watches uses the photoelectric method to sense the pulse which is again divided in Transmission Type and Reflection-Type.

Find more in the link below.

How smartwatch sense and measure heart rate

Working Principle of a Oxygen Saturation (SpO2) Sensor

Oxygen saturation is defined as the measurement of the amount of oxygen dissolved in the blood. This measurement is based on the detection of Hemoglobin (HbO2) and Deoxyhemoglobin (Hb, the form of hemoglobin without oxygen).

Find more in the link below.

How does smartwatch sense Oxygen Saturation (SpO2) Level

Working Principle of a Temperature Sensor

Not all smart watches have this feature. Samsung Galaxy can read the change of temperature. But there is a T01 smartwatch which has a metal sensor on top of the screen making it easy to check for your body temperature. Just raise your wrist and touch the metal plate on your forehead to check for your body temperature.

Working Principle of a Glucose Sensor

Glucose or sugar sensors come in either a discrete form (blood glucose meter test strips) or wearable form (a continuous glucose monitor). Although the form factors look different to the user, both types of glucose sensors use similar detection methods. For example, a glucose oxidase biosensor could be in the form of a test strip or a wearable CGM (continuous glucose monitor) sensor.

Find more in the link below.

Glucose sensor - A Revolutionary sensor for smartwatch

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