User Manual

ZSTAR3 Sensor Board Description
ZSTAR3 Reference Design Manual, Rev. 0.1
Freescale Semiconductor 3-19
Preliminary
Pr
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l
i
m
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n
a
ry
– in Stop3 mode, 700nA
– in Wait mode, 560µA
– in Run mode, 6.5mA
• Triaxial accelerometers
— low-g triaxial analogue Sensor MMA7360L
– in Sleep mode, 3µA
– in Normal mode, 400µA
— low-g triaxial digital Sensor MMA7450L
– in Sleep mode, 5µA
– in Normal mode, 400µA
It is obvious that in a battery operated application care must be taken to ensure the lowest possible current
consumption, especially when the maximum current (provided by the battery) is somehow limited. A
CR2032 Lithium battery cannot provide current in the range of 40mA for long periods of time. To alleviate
high current surges, an additional large capacitor has been designed.
For transmission and reception using the MC13191, a specific scheme has been used to ensure the battery
is not depleted or overloaded. Targeting a 30 samples per second (33ms period) transmission rate. For
better power managment software using system of skiping transmission if sensor data are same or very
similar as in previous trasmit sample. Maximum count of skip trasmission is 10, then sensor data are
always transmitted and by this way is clear Timout timer in USB Stick. The ZSTAR3 typically open
receive window each 10th period (~333ms) to keep synchronization with USB Stick (Communication
Master) and for receive possible control data from master.
The following scheme for one transmission/sleep cycle is used for the typically data transfer:
Figure 3-4. Transmission/Sleep Cycle Details by basic 30Hz datarate
As shown on the previous diagram, all parts of the Sensor Board remain most of the time in
Sleep/Doze/Stop modes, in which the total current consumption is below 10µA.
time
Received Master
Doze
MC13213 RF MODEM:
Stop
MC13213 MCU:
Run
Stop
Sensor
being
measured
TX
RX
NOT TO SCALE
Doze
data
transmitted
Pylon Message
Set up new message
and set RF modem
Run
Plan next RX window
Stop
Trasmit time depends on sensor index