Teardown Tuesday: Bluetooth Toothbrush - LEKULE BLOG


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Sunday, 18 September 2016

Teardown Tuesday: Bluetooth Toothbrush

Ever heard of an app-enabled toothbrush? Want to see what's inside of one?

Continuing with the trend that all devices need to be Bluetooth or Wi-Fi-connected, Philips has made a Bluetooth-connected toothbrush! Philips makes several Bluetooth-connected toothbrushes, but this one is their children's version.
This toothbrush has an associated app for android and apple devices. This particular model is the HX6340.

The app-enabled toothbrush. Image courtesy of Philips.

Opening It Up

Easy open!

It seems like I’ve been saying this a lot lately, but this might have been the easiest device to open yet! A small flathead screwdriver was used to pull the bottom away from the rest of the toothbrush housing. The internal electro-mechanical assembly was then able to be slid out from the plastic housing as an entire assembly.

Circuit Board

Toothbrush PCB Bluetooth
The toothbrush's circuit board

There is a single circuit board inside of this toothbrush that contains numerous surface mount components. There is white silkscreen and an Electroless Nickel Immersion Gold (ENIG) surface finish.
There are 27 test points and a programming header located on this circuit board. Holding this circuit board in place are two plastic clips and several through-hole leads.

Test Points and Programming
The programming and test points on the PCB

Microcontroller and Bluetooth Radio

The Bluetooth SOC in the Toothbrush
The Cypress Bluetooth SOC

Controlling all of the operations of the toothbrush is a Cypress Semiconductor Bluetooth SOC, part number CY8C4247LQI-BL483. This is an ARM Cortex-M0 based microcontroller with a Bluetooth radio built in. This system on a chip is in a 56-pin UFQFN exposed pad package.

Bluetooth Antenna
The Bluetooth trace antenna

To transmit the Bluetooth signal, there is a trace antenna on the bottom edge of the PCB. Unlike some wireless applications, this Bluetooth connection is only intended to operate within a range of a few feet.

Battery and Charger

The Sony Lithium Ion Battery
The Sony Li-ion battery

Powering this toothbrush is a single cylindrical Li-Ion cell Li-Ion. Based on the labeled this battery is manufactured by Sony and carries part number 4235 010 27875. This battery has spot welded tabs that are then soldered to the circuit board. This cell appears to be a Sony SE US14500V with a nominal capacity of 680mAh.

The Wireless Charging Coil
The induction charging coil

Located at the bottom of the assembly is a relatively large coil of wire. This coil of wire is used for the wireless charging on this toothbrush.
The battery charging through wireless power transfer is handled by a small 8-pin IC on the right side of the PCB.

The charging IC

Oscillation Mechanism

The MOSFETs that control the Electromagnets
The FETs that control the electromagnets

Inside of this toothbrush there is a relatively complex electromechanical assembly to produce the oscillations at the head of the toothbrush. The electrical lever there is connected to two MOSFETs to allow the microcontroller to control the magnets. These FETs are in an 8-pin exposed pad package.

One of the electromagnets in the toothbrush
One of the electromagnets

The FETs control two electromagnets. These electromagnets are pulsed at around 250Hz.
Below is an oscilloscope capture of the power going to the electromagnet. The magnetic fields that these produce cause a neodymium magnet to oscillate.

Oscilloscope Capture
The pulses to the electromagnets

This observation, 250Hz per electromagnet, is in line with 31,000 strokes per minute that Philips claims!
The neodymium magnet is joined through a series of mechanical linkages to the head of the toothbrush. The head of the toothbrush is welded together with several spot welds.

The mechanical oscillation mechanism

The App

The companion app Philips has written for this toothbrush is worth a mention. Keep in mind this toothbrush is intended for children.

Thanks for looking at this 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.
My goal with BLOG is to help you learn Electrical.

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