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  • Writer's pictureSubir Biswas

Inside of a Smartwatch | Tech-Knowledge

Updated: Jul 17, 2022

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 provide a historical value to the user and identify the changes happening every day and trigger 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 a OnePlus smartwatch. It is a very interesting topic to get a smartwatch inside. For this article, I’ll be using the reference photos from the OnePlus smartwatch. However, the basic architecture is very common and followed by most of manufacturers. Let’s start..

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.

The followings 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 depending on requirements and features.

Here are a few main component details from the Motherboard:

  • Bluetooth SoC

  • Battery charger SoC

  • Accelerometer

  • Gyroscope

  • Audio Codec

  • Audio Amplifier

  • Memory

  • Microcontrollers

  • Location Controller

Here are a 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 smartwatches use the photoelectric method to sense the pulse which is again divided into Transmission Type and Reflection-Type.

Find more in the link below.

Working Principle of an 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 haemoglobin without oxygen).

Find more in the link below.

Working Principle of a Temperature Sensor

Not all smartwatches have this feature. Samsung Galaxy can read the change in temperature. But there is a T01 smartwatch which has a metal sensor on top of the screen making it easy to check 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.

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