Esprit "IT for Mobility" 26900
context awareness
results & data
research papers
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seminars & demos


Accelerometers sense acceleration in a certain direction. The acceleration can be dynamic (movement, for instance) or static (e.g. position). We used the ADXL05 analog accelerometers in the first TEA board. They only measure acceleration in one direction and output a voltage that is proportional to the measurement. The TEA2 board contains an ADXL202 that outputs measurements for two directions (X and Y) in duty cycles (also called Pulse Width Modulation). Both sensors come from Analog Devices. Photodiodes are basically light sensors. They output a higher voltage if there is more light, and a lower voltage if there is less light. The measurements can be executed very rapidly, which makes it possible to detect frequencies of a lot of artificial light sources - something that is not possible with the human eye.
Temperature sensors
Touch sensors

the DS1820 temperature sensor
Temperature sensors or thermometers can be used as biosensors (to measure body temperature), or environmental sensors. We used the Dallas DS1820, which outputs the current temperature in degrees Celsius with a resolution of 1/2 degree. A software driver is needed to communicate with this sensor, since it has its own communication protocol. Touch sensors are basically two pieces of metal that measure the conductivity of the skin (if there is contact between the skin and the two pieces). We experimented with rings and plates, but the values tend to be very different from person to person.

small microphone
CO sensors
The microphone is a difficult sensor since it usually needs additional circuitry and high-speed processing to get a decent output. It is an important sensor, though, that gives valuable information on the environment.  The carbon monoxide (CO) sensor is a sensor that needs to be heated first, and requires a lot of energy (almost an entire 9V battery on the TEA1 board) to run. We included the Figaro CO sensor in TEA1, but since it needs a lot of resources it was left out the TEA2 configuration.
Pressure sensors

big microphone (left) and ADXL05 accelerometer
Infrared sensors
The Motorola MPX4115 was used in the TEA1 board to detect absolute air pressure. It is generally used in altimeter and barometer applications. The pressure range varies between 5 and 120 kPa.  We used a passive InfraRed (IR) sensor from Seltec GmbH to measure movement (via heat-radiation) outside the TEA device. It can recognise movement from up to five meters, depending on the direction (the detection angle is approx. 90 degrees). Experiments with in non-mobile applications were very promising, it is less usuable for a mobile device, though.
last update: 27/06/2000 by Kristof Van Laerhoven the previous sites can still be found here and here