Teardown Tuesday: Bluetooth Bathroom Scale

In this Teardown Tuesday, we are going to take a look inside an app-enabled Bluetooth bathroom scale!

Today Wi-Fi and Bluetooth-enabled devices synced to apps are very popular, particularly when it comes to tracking health metrics. Let's see what's inside a Bluetooth bathroom scale.

The Bluetooth Scale Used in This Teardown
The Bluetooth scale used in this teardown
Through its Bluetooth connection, this scale pairs to a free Android and iOS app. The particular scale used in this teardown is a 4042565 by A8POWER that was purchased from Amazon. This scale features a backlit LCD display and body fat sensors. It is powered by two included AAA batteries.


The Top of the PCB in the Bluetooth Scale
The top of the PCB in the scale

The PCB in this Bluetooth scale is pretty typical. The board appears to be made out of FR4 with green solder mask and white silkscreen on both sides of the PCB. The pads on the PCB appear to have an electroless nickel immersion gold (ENIG) finish on them.
Nearly all of the components are surface mount. The only two components that are not surface mount are two oscillators. The main microcontroller is a chip-on-board IC covered by a blob of epoxy. The surface mount components appear to be machine-placed and the sensor connections appear to hand-soldered.

The Bottom of the PCB on the bluetooth scale  
The bottom of the PCB in the scale

Bluetooth Module

The bluetooth LE module in the scale 
The iNet BM02 Bluetooth module

The key component to a Bluetooth bathroom scale is its Bluetooth module. The module inside of this scale is a BM02 V3.0 manufactured by iNet. This module has a trace antenna and uses a Dialog Semiconductor DA14580 as its Bluetooth SOC.
The DA14580 supports Bluetooth low energy 4.2 and contains an ARM Cortex M0 microcontroller. Dialog Semiconductor lists Human Interface Devices, Health & Fitness, Medical, Proximity & Beacons, and Smart Home as possible applications for this IC.

Weight Sensors

One of the 4 weight Sensor Assemblies
There are four of these weight sensors

This scale uses four weight sensors, one on each corner, to determine the weight of the person on the scale. These weight sensors are metal loops that flex when weight is applied to them. Underneath the white silicone, there is a flex sensor adhered to the metal loop.

The Flex Sensor on the Bluetooth Scale
The flex sensor adhered to the metal


The LCD on the Bluetooth Scale
The LCD display on the scale 

To relay the information back to the user, a relatively large LCD display is used. This 74x38mm display is comprised of 34 controllable segments. Two 0603 white LEDs provide the backlight on the display. The display connects to the circuit board through a zebra connector.

Wire Management 

The Wire Management in the bluetooth scale
The wire management in the scale

Rather than using wires that are tied to length, this Bluetooth scales uses long wires coming from the sensors. The excess wires are bunched together and taped in place. These wires coming from the body fat sensors and weight sensors are then soldered to surface mount pads on the PCB.

The hand soldered wires on the bluetooth scale
The wires are soldered directly to the surface mount pads


Today, Bluetooth radios are finding their way into everything; this Bluetooth-enabled scale is another example of that. Thanks for reading this week's Teardown Tuesday! Stop by next Tuesday for another teardown.
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Hi, I`m Sostenes, Electrical Technician and PLC`S Programmer.
Everyday I`m exploring the world of Electrical to find better solution for Automation. I believe everyday can become a Electrician with the right learning materials.
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