Wireless Home Automation

1
Wireless Home Automation

• Douglas Brown
• Eric Livergood
• Chris Lotysz

2
Objective

• The short term goal of this project was to use a
  computer to turn on and off a light, as well as
  monitor a door, via wireless communication
• The real objective was to create a basic
  framework for a home monitoring system. New
  devices can easily be added to the system. Only
  new hardware for different sensors/controllers
  would need to be designed.

3
Original Design

• Base module that communicates to the computer via
  serial connection, as well as with all the
  external devices
• Light control device that reports light status,
  can turn a 120 VAC light on and off, as well as
  to a dim setting
• Door monitor reports open/closed status of the
  door
• User interface controls the system and gives the
  commands/requests to the rest of the system

4
Original Design

• Communication
• 2.4 GHz Wireless Transceivers (Nordic 24E1)
• Basic ACK/NACK Protocol
• Frequency Hopping

5
Original Design
Base and Device General Layout
6
User Interface

• Multithreaded Java Swing GUI
• Easy-to-use changes can be made with a single
  click
• Real time updates of wireless devices statuses as
  they are collected
• Easily expandable code to include future devices
  and controls

7
Control Loop

• Device Communication Thread
• Check Event Queue for new actions to perform
• Perform actions, as needed
• Gather all Light Statuses
• Gather all Door Statuses

8
Serial Communication

• To perform any action or request, the program
  sends 2 bytes
• Byte 1 Address of device
• Byte 2 Command/Request
• Wait for confirmation from base station
• Response will always be 1 byte containing the
  status of the device request/command was made to

9
Interrupts

• Serial Port Interrupt
• When data is sent, a flag is set to true to tell
  control loop to begin waiting for response
• When data is available on the serial port, a flag
  is set to tell control loop to read response
• Event Interrupt
• When the user clicks an action, an interrupt
  occurs and the users action is added to the
  event queue

10
Timeouts

• Timeouts are coded into two places in the system
• The base station reports a timeout back to the
  computer if it does not hear back within 200 ms
  from the device it is communicating with
• The control loop will report a timeout if it does
  not hear from the base station within 1500 ms
• Prevents timeouts from creating major delays in
  the system response

11
Wireless Communication

• Base serves as a dummy module to PC
• Underlying communication protocol transparent to
  PC
• Device modules transmit only when directed to

12
Wireless Communication

• PC to Device

Command
SuccessStatus OR Fail
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Wireless Communication

• Device to Device Instruction

14
Wireless Communication

• Device to Device Request For Data

15
Wireless Communication

• Instructions
• Light ON 0x00
• Light OFF 0x01
• Get Light Status 0x02
• Get Door Status 0x10
• Dim Light 0x4X (X indicates the level of dim)

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Wireless Communication

• packet.address GetChar()
• packet.operation GetChar()
• switch(packet.operation)
• case NEW_INSTRUCTION
• //Any calculations or base operations
• SendInstruction(packet)
• case NEW_GET_STATUS
• //Any calculations or base operations
• status SendRequestForData(packet)
• PutChar(status)

17
System Response

• Steps taken to decrease response time
• Increased resolution of checking for data
  availability
• Decreased the number of bytes sent between the
  devices
• Only refreshed user interface screen when changes
  have been made
• Created separate thread to handle serial
  communication

18
Hardware

• Objectives Wireless communication,
  microcontroller, reliable power supply,
  interrupter sensor, digital switch control of
  120VAC
• nRF24E1 programmer board was chosen to simplify
  the blending of wireless communication with
  microcontrol

19
Hardware Cont

• Battery power supply and wall delivered power
  supply both necessary.
• Battery power for remote, sensor based modules
  (door)
• Wall power for base station and for modules with
  available wall power (light)

20
Base Station

• Power Supply and Transceiver
• Wall delivered power instead of 9v
• Serial communication from transceiver board to PC

21
Light Module

• Digital Control of Light with multiple dimming
  options

22
Light Module Cont

• The relay chosen determines the resistive path
  taken and thus the voltage delivered to the gate
  of the Triac.
• The Triac turns on allowing current to flow to
  the light bulb when the gate voltage is
  sufficiently high.
• The relays are DC controlled via I/O pins from
  the transceiver board.

23
Door Sensor Module

• Uses a photo interrupter to determine the doors
  status then transmits its status via the
  transceiver board

24
Door Module Cont

• 9V battery supplied power.
• Sensor used the 3V regulated power and the
  straight 9V battery power.
• When door is closed power consumption is minimal,
  however when the door is open the sensor
  dissipates much more power

25
Power Analysis

• Door
• Transceiver sinks 18mA at 3V or 54mW
• Always putting out 24Vs on the relays(or120V)
• 
  Off(24VAC On(120VAC)
• Relay1 13.4K 3.0mA 42.3 mW 1.0746 W
• Relay2 13K 3.1mA 44.3 mW 1.1077 W
• Relay 3 12.4K 3.2mA 46.4 mW 1.1613 W
• Only one relay on at a time
• Additional power loss in the triac itself. Heat
  created and leaked through a heat sink
• Base
• Transceiver only 54mW wall delivered

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Power Analysis Cont

• Door
• 9v Alkaline Battery supplied power
• 600 mAh per 9v 5400mWh
• 3v regulated and 9v unregulated (Vcc)
• Transciever 54mW
• Sensor Diode 40.5mW Open 40.5mW
• Life when door is open 40hrs

27
Hardware Testing

• The dimming resistances were determined
  experimentally by controlling a triac with a
  potentiometer
• Power circuits were constructed and tested with a
  voltage meter. No testing for consistency was
  conducted, but repeated checking of voltage
  showed the voltage regulator to be reliable

28
Testing Development for PIC

• 7 Phases
• Serial Communication
• Timer Setup
• Simple Wireless Communication
• Complex Wireless Communication
• Integration of Serial Wireless
• Protocol Implementation
• Testing with PC

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Software Testing

• Created a PIC Simulation
• Two computers, one with user interface, the other
  with PIC Simulation
• Output to console each step
• Output the data being sent, the data received,
  how the data was interpreted
• Ran program with one or all devices off to ensure
  timeouts would be handled appropriately

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Successes

• Communication interference less than expected,
  frequency hopping unnecessary
• A very open-ended, easy to use framework
  developed for expansion of project

31
Challenges

• Range
• Security
• Power consumption
• Cost

32
Ethical Considerations

• Introduction of another potential surveillance
  system
• Potential for unwanted outsider control
• Creating a safe system

33
Acknowledgements

• Nordic Semiconductor
• Microchip
• Professor Scott Carney
• Ishaan Gupta
• Tim OConnell
• Sparkfun