Hardware Components

Some images taken from http://www.cs.uni-paderborn.de/index.php?id=1119&L=1

Overview

Controller

• CPU of the node
• microcontrollers - processors designed for embedded systems
• Crossbow Mote - Imote2 = Intel PXA271 XScale CPU (13-416MHz)
• SPOT - 180MHz 32-bit ARM920T core processor 
• Dynamic Voltage Scaling - adjust speed of processor to control energy consumed.

Memory

• Nodes typically have a small amount of RAM and some flash.  Flash typically incurs long read/write access delays and requires significant energy for access.
• Imote2 - 32MB FLASH, 32MB RAM 
• SPOT - 512K RAM and 4M Flash 
  

Communication Device 

• Nodes typically use RF-based communication.  
• Long range
• High data rates
• Acceptable error rates
• Reasonable energy expenditure
• No line of slight required
• Imote2 - 802.15.4 radio, 250kb/s data rate, 30 meters
• SPOT - 802.15.4 radio, 80 meters 
• Transceivers typically half duplex; cannot send and receive at the same time
• Typically support 4 states: transmit, receive, idle, sleep
• Often transmission power control is adjustable.  More power used to transmit = greater range.
• Some simple transceivers lack unique address.  SPOT have 64-bit IEEE address (analogous to MAC address).

Sensors and Actuators

• Sensors 
• Passive, omnidirectional - thermometer, light sensor
• Passive, narrow beam - camera
• Active - radar
• Actuators - "open or close a switch or relay" (e.g., light bulb, motor)

Energy Management

• Significant  concern for sensors
• Most components of node can be turned off or put into low-power state when not in use (radio, controller, sensors)
• Transitioning from low-power mode to operational costs time and energy

OS/Programming Environment

• Imote2 - TinyOS, nesC
• SPOTs - Squak VM on hardware

Date: 2008-04-18