Information Technology Reference
In-Depth Information
4.4. Sensor Nodes, STIM
The sensor nodes are 8 bit microcontroller based solutions. They are able
to control eight different transducers and they have a Bluetooth chip, the LMX9838. It
communicates with the microcontroller using a serial communication interface, and it has
implemented the Bluetooth protocol stack until the SDP layer.
The software in the microcontroller sends the information via serial lines in messages
defined by the Bluetooth chip manufacturer (national semiconductor).
The established Bluetooth connection uses the RFCOMM protocol to emulate a serial
point to point communication between the sensor nodes and the sensor manager using radio
signals.
4.5. Sensors and TEDS
The IEEE 1451.0 standard defines the so called Transducer Electronic Data Sheet or
TEDS. These files are data structures divided in perfectly defined different fields. The
information within these fields describes the sensor itself.
Using the information of these files the application layer can easily know every
parameter of the sensor that is controlling, for instance calibration information, sensor's
measuring ranges or maximum and minimum working temperature of the sensor.
One of the most useful characteristic of these files is that they can store the information
for the conversion from the sensor's output voltage value to its corresponding physical units.
These characteristic makes easier the management of the transducers giving to the application
a transparent interface to work with them, regardless of the physical characteristics of the
transducer in question.
An example of a calibration TEDS code for the LM35 temperature sensor is shown here:
XDCR12_CAL_TEDS_SIZE, /* Total Length */
0x03, /* TEDS identification header */
0x04, /* Length of TEDS */
0x00, /* Family */
0x05, /* Class / Access code */
0x01, /* Version of the standard */
0x01, /* Tuple length */
0x0A, /* Last calibration date */
0x08, /* Length of field */
0x4A, 0x43, 0xD7, 0x40, /* Jun 25, 2009, 20:00:00 */
0x00, 0x00, 0x00, 0x00, /* See above */
0x0B, /* Calibration interval */
0x08, /* Length of field */
0x01, 0xE1, 0x33, 0x80, /* 1 year */
0x00, 0x00, 0x00, 0x00, /* See above */
0x0C, /* SIConvrt */
0x0C, /* Length of field */
0x1E, /* SISlope */
