Stanford Wockets Activity Project (SWAP)
Wocket Monitoring System Equipment
Monitoring system consist of a smart mobile phone (HTC Touch Diamond2), 4 motion sensors (Wockets), 4 bands for holding a Wocket on the dominant wrist and ankle, two pocket pouches for carrying a Wocket in a pants pocket besides two chargers, one for charging the phone and other for charging the Wockets.
HTC Touch Diamond2
The phone is a touch screen “smart” mobile phone that has a variety of usual “smart” phone functions which include
- making and receiving calls
- sending and receiving text messages
- sending and receiving e-mail
- accessing the internet, and
- taking and sending pictures.
The phone you will be provided (project phone) will have custom software that allows it to receive information from the two activity sensors (Wockets) you will wear or carry, store these data on the phone and automatically send (upload) these data to a secure server (some during the day but most of it at night).
Wockets
The Wocket physical activity monitoring system consists of two custom-designed wireless motion sensors/transmitters (Wockets) and a mobile phone.
- Each Wocket contains a triaxial accelerometer, a microprocessor, a Bluetooth transmitter and a small rechargeable battery.
- The unit is encased in a light plastic that makes it flexible (so it can bend slightly around the wrist or ankle) and is water resistant but not waterproof (should not be submerged). It is 2.2 inches x 2.0 inches x 0.25 inches in size and weighs 0.38 oz.
- Each unit fits in a custom cloth/Velcro band with one worn on the dominant wrist and the other on the dominant ankle.
- The Wockets are charged using a specially made charger strip that has slots to charge two Wockets simultaneously. For a full charge they should be charged for about 3-4 hours and the charge last for up to 30 hours.
- The accelerometer in each unit detects any movement of the wrist or ankle (triaxial = movement up or down, front to back and side to side), stores these data briefly on the custom programmed memory chip and then this information is sent to the mobile phone by the Bluetooth transmitter once each minute.
- The accelerometer detects movement at a rate of 40 times per second (40 Hertz) and these data are called raw accelerometer data.
For more technical information about the Wockets click here.
Data Collection
The mobile phone is able to receive these signals, store them in memory, and perform limited processing. Using the data connection on the phone, small amounts of the motion sensor data (summary data which is raw accelerometry data averaged for a minute) are sent automatically each hour via wireless to a project secure server for monitoring and problem detection by project staff.
The chart below shows summary data recorded from 10:30 AM to 3:30 PM while the subject was alpine skiing at a ski resort. It is easy to see the motion while skiing and the resting in between while on the chair lift. Lunch was eaten between 1:15 and 1:45pm.
Each night, when the phone is being charged, it will automatically send the raw accelerometry data collected from your Wockets that day to the secure server using the phone’s wireless connection. This raw data allows for much more detailed analysis of your activity or inactivity throughout the day.
The figure below shows the movement of an MIT scientist as he moves about the day walking, riding the subway, sitting at meetings or dinner, around home in the evening and then while sleeping.
