User Manual
Table Of Contents
- Revision History
- Table of Contents
- Chapter 1 Introduction
- Chapter 2 Wireless Sensing Triple Axis Reference design introduction
- Chapter 3 Sensor Board description
- 3.1 Board overview
- 3.2 A/D conversion of XYZ levels
- 3.3 Power management
- 3.4 ZSTAR Sensor Board hardware overview
- 3.4.1 Analog connections
- 3.4.2 g-select connections
- 3.4.3 BDM (Background Debug Mode) connections
- 3.4.4 Sensor Board schematics
- 3.4.5 Button connections
- 3.4.6 MC13191 to MC9S08QG8 microcontroller interface
- 3.4.7 MC13191 RF interface
- 3.4.8 Clocking options of MC9S08QG8
- 3.4.9 LED indicators connections
- 3.4.10 Power supply
- 3.5 Bill of Materials
- Chapter 4 USB stick board description
- Chapter 5 Software Design
- 5.1 Introduction
- 5.2 SMAC (Simple Media Access Controller)
- 5.3 ZSTAR RF protocol
- 5.4 STAR protocol and ZSTAR extensions (over USB)
- 5.5 Bootloader
- Chapter 6 Application Setup
- Appendix A References
Power management
Wireless Sensing Triple Axis Reference design, Rev. 0.9
Freescale Semiconductor 19
• 8-bit microcontroller MC9S08QG8
– in Stop mode, 750nA
– in Wait mode, 1mA
– in Run mode, 3.5mA
• low-g triaxial sensor MMA7260Q
– in Sleep mode, 3µA
– in Normal mode, 500µA
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 - see 3.4.10 Power supply.
For transmission and reception using the MC13191, a specific scheme has been used to ensure the
battery is not depleted or overloaded. Targeting a 20 samples per second (50ms period) transmission
rate, the following scheme for one transmission/sleep cycle is used for the data transfer:
Figure 3-4Transmission/sleep cycle details
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.
During each loop, once the data has been acquired from sensor, transmission over the MC13191
transceiver is initiated. The current consumption of the transmitter is ~30mA at that time, but only for a
short period of time (typically ~600µs).
In order to keep the sensor board informed on the status of connection (for example, if the data-receiving
side - USB stick - is out of range, disconnected, etc.), the reception has to be turned on after the data has
been transmitted. This is not really required within each loop cycle, and in the actual implementation only
on every 8
th
loop the receive window opens (receiver is enabled to receive the acknowledgment). More
in the 5.3 ZSTAR RF protocol description.
time
Sleep
wake-up
Normal
MMA7260Q:
Doze
MC13191:
Stop
MC9S08QG8:
Stop
Sleep
Run Stop
Sensor
stabilizes
Sensor
being
measured
TX
Wait
Wait
RX
optional
receive
window
NOT TO SCALE
Doze
data
transmitted