Alec Woo
Jan 15th, 2002
NEST Retreat

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Need a set of different sensors to support
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 common sensing applications potential NEST specific applications
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A “mega” sensor board
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Flexibility to select what sensors to populate rather than building many specialized sensor boards
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Under the constraints of
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Physical size, structure
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“Pin” estate
Energy consumption
Cost

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Goal
Board overview
Hardware Interface
Tour of individual components

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Selected sensors for the MICA sensor platform
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Photo (light) sensor
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Temperature sensor
Microphone
Single Tone Sounder
2 Axis Accelerometer
2 Axis Magnetometer
Each module is independent

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Size
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 same dimension as the Mica board make space for Mica’s switch and LEDs
4-Layer Board
 with a ground plane
Top and bottom 51 pin connectors
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Stay on the top of a stack of daughter cards

1.25 in
Microphone Sounder Magnetometer
Temperature
Sensor
Light
Sensor
2.25 in
Accelerometer

Mica PINS
TEMP
Y Axis
X Axis
MAGNETOMETER
PHOTO SOUNDER
Tone
Intr
Mic
Signal
MICROPHONE
Gain Adjustment
ACCELEROMETER
Y Axis
X Axis
ADC Signals (ADC1-ADC6)
On/Off Control
I 2 C Bus
Interrupt

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Goal
Board overview
Hardware Interface
Tour of individual components

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Photoresistor
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Clairex CL9P4L
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Simple voltage divider design
PHOTO
INT1
ADC1

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2 options for thermistor
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High Precision, less range
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YY14406
10kohm, +/- 0.2 C o , ranging 0-75C o
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Expensive: $6/unit
Low Precision, more range
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ERT-J1VR103J
10kohm, 1C o accuracy, -40 to 125C o
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$0.43/unit @1000
Voltage Divider Design

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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

Pre Amp Passive RC
High pass and
Low pass filters
Amp mic_out
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Pre-amplifier (MAX 4466)
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Fixed amplification of -56
Passive bandpass filters ~4.7mA for circuit prototype
+ microphone
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159Hz – 6.4kHz
Amplifier (MAX 4466)
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Adjustable amplification from -5 to -56

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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
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Large energy consumption
Potential influence on magnetometer

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Piezoelectric single tone buzzer
Resonant at 4kHz +/- 0.5kHz
85dB sound pressure at 10cm
Circuitry + sounder draws ~2mA

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Biquad Active Filter Circuitry
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P. 278, The Art of Electronics mic_out
Active
Bandpass
Filter mic_bandpass_out Tunable
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 center frequency(f o
) and bandpass bandwidth (BW)
Bandpass bandwidth determines quality of the filter
Center frequency can shift while bandpass bandwidth remains the same
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 f o
= 1/2  R
F
C
BW = 1/2  R
B
C
Default setting
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Center frequency is 4kHz with 800Hz bandwidth

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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
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Phase lock loop filter can be sampled directly to obtain information estimate time of flight with time synchronized RF signal

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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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Directly connected to Mica’s ADC channels
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Duty cycle output
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Not used but signals are fanned out to pads on board
$15/unit

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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 2 nd stage amplification to avoid railing on each axis
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Amplifiers are not Rail-to-Rail (0.66V to 2.33V)
Pads on board to allow easy access to demagnetize the chip
$20/unit

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 http://www.cs.berkeley.edu/~awoo/micasb
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Schematics
Layout
Gerber files
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Bill of Materials
Delivery
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30 boards on Feb 5 th
Crossbow ready around March 1 st
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1) basic sensors
2) basic sensors + magnetometer + accelerometer

MUX Setting Sensors or
Actuators
Light
Temperature
Sounder
Microphone
PLL Signal
Tone Detector
Accelerometer
Magnetometer
Signal
ADC1
ADC1
-
ADC2
ADC2
PW3
PW3
INT3
ADC3,4 PW4
ADC5,6 PW5
Power
Control
INT1
INT2
PW2
PW6 = 1
PW6 = 0