June 2008 WEI Short Course 1 Wireless Embedded InterNet working Foundations of Ubiquitous Sensor...
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June 2008WEI Short Course 1
Wireless Embedded InterNetworking
Foundations of Ubiquitous Sensor Networks
EPIC – Open Embedded Networking Platform
David E. CullerUniversity of California, Berkeley
June 2008WEI Short Course 2
On-line reference
• http://www.eecs.berkeley.edu/~prabal/projects/epic/
June 2008WEI Short Course 3
Epic Core
June 2008WEI Short Course 4
Overview
2 binaryInputs
2 binary Outputs
Convert switch to digital value
external voltage sel.
4 analogInputs
signal conversion
Epiccore
Trim Pot
Power pins
IO pinsus
er b
utto
n
rese
t but
ton
Alkaline battery
Li Ion battery
USBEpicUSB
LED
s
5v TTL reg
June 2008WEI Short Course 5
Turning a switch into a digital input
• Many sensor are switches
• Two “states” but not digital– Open => no current
– Closed => no voltage drop
• Cap charges to Vacc when open
• Cap discharges to GND when closed
Vacc
GND
switch
D
VD
VtL
VtH
June 2008WEI Short Course 6
Digital Inputs
June 2008WEI Short Course 7
Digital Outputs
• Two screw terminals provide access to digital outputs
• Output voltage selected by jumper
• Feeding through pFET– Closed when gate is Low
• Gate controlled by MCU pin
• Port 5.0 => Dout0
• Port 5.1 => Dout1
June 2008WEI Short Course 8
Ratiometric sensor
• Va = Vacc* Rsens / (Rcomp+ Rsens)
• use Vref = Vacc
• D = M * Rsens / (Rcomp+ Rsens)
Vacc
GND
Resistive Sensor
VA
Rcomp
Rsensor
June 2008WEI Short Course 9
Analog Inputs
June 2008WEI Short Course 10
Analog Inputs (cont)