Transcript Mica Sensor Board Review - University of California, Berkeley

The Mica Sensing Platform
Alec Woo
Jan 15th, 2002
NEST Retreat
Goal
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Need a set of different sensors to support
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A “mega” sensor board
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common sensing applications
potential NEST specific applications
Flexibility to select what sensors to populate rather
than building many specialized sensor boards
Under the constraints of
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Physical size, structure
“Pin” estate
Energy consumption
Cost
Outline
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Goal
Board overview
Hardware Interface
Tour of individual components
Components
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Selected sensors for the MICA sensor
platform
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Photo (light) sensor
Temperature sensor
Microphone
Single Tone Sounder
2 Axis Accelerometer
2 Axis Magnetometer
Each module is independent
Board
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Size
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4-Layer Board
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same dimension as the Mica board
make space for Mica’s switch and LEDs
with a ground plane
Top and bottom 51 pin connectors
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Stay on the top of a stack of daughter cards
Device Placement
Microphone
Sounder
Magnetometer
1.25 in
Temperature
Sensor
Light
Sensor
2.25 in
Accelerometer
Hardware Interface
Mica PINS
PHOTO
SOUNDER
Mic
Signal
MICROPHONE
TEMP
Y Axis
X Axis
Tone
Intr
Gain Adjustment
MAGNETOMETER
ADC Signals (ADC1-ADC6)
On/Off Control
I2C Bus
Interrupt
Y Axis
X Axis
ACCELEROMETER
Outline
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Goal
Board overview
Hardware Interface
Tour of individual components
Photo Sensor
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Photoresistor
Clairex CL9P4L
Simple voltage divider design
INT1
PHOTO
ADC1
Temperature Sensor
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2 options for thermistor
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High Precision, less range
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Low Precision, more range
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YY14406
10kohm, +/- 0.2 Co, ranging 0-75Co
Expensive: $6/unit
ERT-J1VR103J
10kohm, 1Co accuracy, -40 to 125Co
$0.43/unit @1000
Voltage Divider Design
Microphone
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Acoustic input with omni directional
microphone
Panasonic WM-62A
draws < 500uA
Flat frequency response from 100Hz to 5kHz
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100Hz to 16kHz from spec
Amplification and Filtering
Pre Amp
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mic_out
Fixed amplification of -56
Passive bandpass filters ~4.7mA for circuit prototype
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Amp
Pre-amplifier (MAX 4466)
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Passive RC
High pass and
Low pass filters
159Hz – 6.4kHz
+ microphone
Amplifier (MAX 4466)
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Adjustable amplification from -5 to -56
Sounder
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Now, we can make sound!
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Great for tracking nodes, debugging,
application user interface, or ranging through
time of flight
Alternative design
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Power amplifier with a generic speaker
Large energy consumption
Potential influence on magnetometer
Sounder
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Piezoelectric single tone buzzer
Resonant at 4kHz +/- 0.5kHz
85dB sound pressure at 10cm
Circuitry + sounder draws ~2mA
Active Bandpass Filter
mic_out
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Biquad Active Filter Circuitry
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P. 278, The Art of Electronics
Tunable
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Active
Bandpass
Filter
mic_bandpass_out
center frequency(fo) and bandpass bandwidth (BW)
Bandpass bandwidth determines quality of the filter
Center frequency can shift while bandpass bandwidth remains
the same
fo = 1/2RFC
BW = 1/2RBC
Default setting
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Center frequency is 4kHz with 800Hz bandwidth
Detecting the Sounder’s Signal
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National LMC567
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Phase lock loop and adjustable amplitude threshold
support to detect tone
Adjustable tracking frequency
Track either the output of the microphone or
active bandpass filter
Detector’s Output
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Raise an interrupt if tone is present
Phase lock loop filter can be sampled directly to
obtain information
estimate time of flight with time synchronized RF
signal
Accelerometer
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Analog Devices ADXL202E
2 Axis, +/- 2g, at 2mg resolution
600uA current consumption
Two types of output
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Raw analog output
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Duty cycle output
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Directly connected to Mica’s ADC channels
Not used but signals are fanned out to pads on board
$15/unit
Magnetometer
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2 Axis Honeywell HMC1002
Range is +/-6 gauss (earth’s field +/-0.5 gauss)
27ugauss at 10Hz
Current consumption is ~5mA
2 stage amplification
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29 * 41 = 1189
2 digital potentiometer to adjust 2nd stage
amplification to avoid railing on each axis
Amplifiers are not Rail-to-Rail (0.66V to 2.33V)
Pads on board to allow easy access to
demagnetize the chip
$20/unit
Further Information
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http://www.cs.berkeley.edu/~awoo/micasb
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Schematics
Layout
Gerber files
Bill of Materials
Delivery
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30 boards on Feb 5th
Crossbow ready around March 1st
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1) basic sensors
2) basic sensors + magnetometer + accelerometer
Signal and Power Interface
Sensors or
Actuators
Signal
Light
Temperature
ADC1
ADC1
Sounder
-
Microphone
PLL Signal
ADC2
ADC2
Tone Detector
INT3
Accelerometer
Magnetometer
ADC3,4
ADC5,6
Power
Control
INT1
INT2
PW2
MUX Setting
PW3
PW3
PW6 = 1
PW6 = 0
PW4
PW5