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)