Version 4



    Parts List


    Component TypeComponent NameDescriptionQuantity
    BUS / InterfaceI2C or SPIInter-Integrated Circuit Communications Protocol or Serial Peripheral Interface Communications Protocol1
    Direct Attach TypeSMDSurface Mount Device Connection Type1
    Wireless TechnologyBluetooth/BLEBluetooth / Bluetooth Low Energy v4+1
    Sound94dB-20Hz to 20kHzStandard (94dB max) + High Quality (down to 20 Hz) + Audible Range (up to 20 kHz)1
    Pressure24bit-110kPA +/- .05kPAHigh Resolution (24 bit) + Standard Atmospheric (110 kPa) + High Accuracy (± 0.05%)1
    Magnetometer16-bitHigh Resolution (16 bit)1
    Gyroscope3 Axes3 Axes - Eg. Pitch / Yaw / Rotation1
    AccelerometerHigh Res - Medium DutyHigh Resolution  (16 bit) + Medium Duty  (± 8.0 G)1
    ColourRGB450 to 750nm1
    LightVisible SpectrumVisible spectrum (peak wavelength 750nm)1
    TemperatureStandard AccuracyStandard Accuracy (±2°C) from -40°C to 105°C1



    I spend many hours a day sitting behind a desk. So do many of my friends and colleagues. Some of them do one or more sport activities before/after work, but a lot of them don't. This is how I got the idea to use a device that would encourage the owner to move in a bit entertaining way. To relief the strain, change body position, stretch and relax.



    sitting behind a desk


    I have noticed a recent expansion of fitness trackers, but most of them are smart watches
    attached to a hand. They tend to track the whole person, which could be limiting. I was thinking about something of a tennis ball size, that would include the sensor board, host MCU and a battery. Small form factor of all the electronics is the only way this could ever be made - ideally with a center of gravity in the intersection of X,Y and Z axis.


    tennis ball in a hand


    Here are some ideas for elementary functions:


    The device could detect movement using an on-board accelerometer, a gyroscope and a magnetometer:

    • detection of a rotational movement - while holding in hand, rotating your wrist, elbow or the whole arm using a shoulder
    • compass heading
    • detection of a free fall - throw the ball in the air and catch it
    • click and double click detection - start and stop the exercise


    On-board pressure sensor is able to provide a pressure difference in time:

    • detection of an altitude difference - for example exercise consisting of climbing 100 stairs.


    I am not a fan of too complicated devices. However, it might be useful to signal some exercise states. Let's say the ball could be made out of some semi-transparent plastic. An RGB LED provides simple state information (changing colour from red to green during the progress) in addition to a small vibration motor (force feedback for every repetition) and an audio output with instructions.


    BLE would be the only data connection to the outside world. A paired cell phone with an application would have to store all the exercise definitions and probably collect the results.


    The question is whether all the sensor data and its precision could be used for real therapy applications or just for having some fun. I don't think that any electronics can currently replace a physiotherapist, however, there are always more people with health problems than can be treated. I guess the only way to find out is to run a proper clinical trial.