Review of WeSU: a development board for wearable applications.


At the recent event “ST = Life Augmented”, held in Milan during the Class Digital Experience Week, STMicroelectronics has raffled various development kits, for attendees who enrolled to the event through the Pepite blog. Apart to the famous STM32 Nucleo-64 board and some of its Expansion Board (the STM32 x-Nucleo), the most interesting thing was the development kit for wearable applications, the STEVAL-WESU 1, valued at approximately 50€ and we were lucky to get one for free.

STEVAL-WESU1 stand for ST EVALution WErable Sensor Unit, and is an evaluation kit to test various sensors brought by ST for a large number of products such as mobile, tablet and now proposes they to build personal wearable devices. On top of the box there is little information about its contents, as to hide the little treasure that encompasses inside, as you can see in Fig.1. We read that the device is compact, which has a dedicated firmware for wearable devices and an APP available for both Android and iOS, but no mention about the hardware components.

The Hardware of WeSU

The STEVAL-WESU package
The STEVAL-WESU package

To know what we’ve got in your hand, before open the box let’s look at the product page on the ST website. The WeSU is described as a compact solution for wearable applications for motion detection, with a complete set of firmware examples. The list of hardware components of the evaluation kit is really remarkable:

  • Microcontroller 32-bit ultra-low-power (STM32L151VEY6)
  • 3D Accelerometer + 3D Gyroscope (LSM6DS3)
  • 3-axis magnetometer (LIS3MDL)
  • MEMS Pressure Sensor (LPS25HB)
  • Processor for Bluetooth Low Energy connectivity (BlueNRG-MS)
  • BALF-NRG-01D3 – 50 Ω balun with integrated harmonic filter for energy saving (STC3115)
  • SWD connector for programming and debugging
  • Micro USB connector for charging
  • Charger for lithium batteries (STNS01)

The Fig.2 show the STEVAL-WESU1 functional block diagram with the various devices’s connections.

STEVAL-WESU1 functional block diagram
STEVAL-WESU1 functional block diagram.

Detection of accelerations and rotations:

The LSM6DS3 is a system in-package with a digital accelerometer and a digital 3-axis gyroscope both operating at 1.25 mA (up to 1.6 kHz ODR) in high performance mode, always allowing the low-power operation. The LSM6DS3 supports major operating system requirements, offering real sensors, virtual and batch, with 8 Kbytes for dynamic batching of data. It has a high strength to mechanical shock. The module has a range of accelerations equal to: ± 2 / ± 4 / ± 8 / ± 16 g and a range of angular velocities of ± 125 / ± 245 / ± 500 / ± 1000 / ± 2000 dps. It is able to operate over a range of temperatures from -40 ° C to +85 ° C.

Detection of magnetic field

The LIS3MDL is a magnetic sensor with three axes ultra-low-power high performance. Full scale is user-selectable between values: ± 4 / ± 8 / ± 12 / ± 16 gauss. It has the ability to self-test that allows the user to control the operation of the sensor on the final application in which it is used. The device can be configured to generate the interrupt signals if it detects a magnetic field.
The LIS3MDL I2C includes a serial interface supports both standard mode and the fast mode (100 kHz and 400 kHz) and standard serial interface SPI. It is able to operate over a range of temperatures from -40 ° C to +85 ° C.

Detection of Atmospheric pressure:

The LPS25HB is a piezo-resistive absolute pressure sensor that functions as a digital barometer. The device comprises a sensing element and an interface that allows communicates via I2C or SPI bus between the sensitive element to the application that contains it. The sensitive element, which detects the absolute pressure, consists of a membrane suspended produced with a special process developed by ST. The LPS25HB is able to operate from -30 to +105 ° C. The package has a hole to allow the external pressure to reach the sensing element.

Power monitoring:

The STC3115 includes hardware functions to implement a cheap meter charger  for battery monitoring. The device uses the current detection, the counting of the Coulomb and accurate measurement of the battery voltage to assess the state of battery charge. An internal temperature sensor allows to simplify the temperature compensation. An alarm output may report the condition to low state of charge or of low battery voltage. The alarm threshold levels are programmable.

The unboxing

Among the various guides that are supplied with the STEVAL-WESU1, we focus on the first “Getting started guides.” Here is listed the contents of the evaluation kit that we can see in the Fig.3

The WESU1 kit unboxed
The WESU1 kit unboxed
  1. WESU card
  2. One rubber support with the shape of a wristwatch
  3. One opaque plastic box closed inside the rubber support
  4. One adhesive Velcro strip
  5. One 100 mAh Li-Po battery inside a red protective plastic bag
  6. One pastic frame with 2 buttons and 1 buckle inside the transparent plastic bag
  7. One adapter board with a flat cable for programming and debugging the WeSU inside the transparent plastic bag

We note that the evaluation kit must be assembled, so with the enthusiasm of a child receiving a Lego kit, we are going to mount the device.

Assembling our WeSU

In the guide are described the basic steps to follow to get to the WeSU the its final form, but here we tell some tips that we have experienced for a trouble-free installation.

Advertise removed
Advertise removed

1. The printed circuit of the WeSU kit has a small rectangular strip that shows the legal notice for the only evaluation use. In order to accommodate the little board inside the transparent container you must cut away this part of the PCB. The first step suggested by the guide consists of the removal of the strip containing the disclaimer.

To proceed we recommend firmly to hold the card by the two sides from the side of the button and use a large head pliers to grab the printed circuit strip to remove. Not over-tighten the plier and slowly turn up from the center of the strip, then from the two ends. Repeating the operation on the other side, the printed circuit strip will be removed without problems, as show in Fig.4.


LiPo Battery connected to the PCB board
LiPo Battery connected to the PCB board

2. In the second step you need to connect the board to the lithium polymer battery. The power connectors of the battery and of the board are very small, so if you force them  you could connect them in a wrong way.

The male connector on the board has three contacts facing up, instead the female battery connector has three holes. The battery connector must be connected with the holes downwards, so that it locks into place without any effort on the card slot. To properly position the card and the battery inside the plastic package should we bend the power cables as shown in Fig.5.


The two parts of the plastic box
The two parts of the plastic box

3. The plastic box, where we will install the WeSU board and battery, will take place inside the wrist’s rubber support with a watch shape.

Once extracted, we recommend to proceed to its opening gradually lifting it from all 4 sides, using a fingernail or the end of the cap of a ballpoint pen. Fig.6 show the two separated parts of the box.


The PCB and battery take place inside the plastic box
The PCB and battery take place inside the plastic box

4. Remove one of the buttons from its support frame. To correctly position the board and the battery inside the box, you must use the lower part of the box as reference (the side without the WESU’s logo impressed) which has angular edges in the four interior corners.

You must position the plastic button in its cavity and then line up the switch button of the board. If you have correctly folded the power wires, the battery will fit perfectly into the gap between the plastic box and WeSU board, as you can see in the Fig.7.


The box and it’s rubber support
The box and it’s rubber support

5. Place the top of the box and close it firmly. The WeSU begins to take the form of a real product rather than that of an evaluation kit, as shown in Fig.8.

Outside of the plastic container are accessible an USB port for connecting to power and a male header for the connection to the programmer/debugger.

6. To turn on the device you must connect it to USB for the first charge using a micro type cable. When the battery is being charged we will see a steady red LED.

Once it reaches the charging the red LED goes off and we will have a flashing white LED that indicates the ON state of the board.

WESU LED status
On the left the WeSU is charging. On the right the WeSU is full charged.


The final form of WESU
The final form of WeSU

7. When the mount is finished and the battery is charged, we can insert the plastic box inside the rubber support to attach on your wrist. The Fig.10 show the WeSU in it’s final form.

We just have to install the APP provided with the evaluation kit to start experimenting with the WESU.


A try to the available apps

From the guide we see that a dedicated WESU’s app is available for both Android and IOS based systems. The last step that remains to do to be able to start to test our evaluation kit is to install this app on our smartphones. We can find it on the Google Play Store or directly to the link addressed by the QR Code drawn on the guide.

The WESU is correctly paired
The WeSU is correctly paired and listed in the node list of the app

The Application ST WESU that contains various demonstrative features of remote sensing, is available for both Android and IoS. The Application ST BlueDFU that allows updating of WeSU driver via Bluetooth is available only for Android.

Once you have installed the app, you only need to start the app and make the Bluetooth pairing between your Smartphone and the WESU. When you successful pair the devices, the WeSU appears in the App’s node list, as show in the Fig.11.

To use all of WeSU utilities we need to install OSX Motion libraries that allow the Activity recognition and the Carry position recognition, using the ST-LINK/V2 programmer as suggested by the quick start guide.

MEMS Library
The OSX Licence Wizard to install the two MEMS library
Testing sensor fusion
Testing sensor fusion

If we test the product “As it is” , we can only use some feature of the application because the functions related to the two libraries do not work. So the app can’t detect the type of activity (walking, running, go on bike, go on motorcycle or go on car) and can’t detects the positioning status (on the table, hand, etc.).

But other features correctly work, like the sensing of the 3D orientation shown in the Fig.13, the remote temperature sensing and the remote data monitor.

In the following image you can see all the features of the WESU’s app:

The various features of the WESU's App
The various features of the WeSU’s App

Particularly interesting is this last feature that is able to display on the smartphone the data generated by the various sensors of the WeSU. It also allows you to store the collected data and send them via email.

This feature coupled with the robustness of the WeSU container brings to mind various possible applications to test this interesting wearable sensing platform.

In the next episode we will try some real-world applications to test the resistance of the kit, its capability of Bluetooth connection and its actual usefulness resolve concrete problems.
See you soon guys.

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