Household Power Measurement System

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Household Power Measurement System

• Group 2

Manuel Rodriguez Frank Ladolcetta Amir
Shahnami Alex Demos
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Project Description

• Meter that will measure the power consumption of
  household appliances
• Send the information wirelessly to an LCD display
• Display the approximate hourly and monthly power
  consumption of the appliance being monitored

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Project Motivation

• Keep track of energy usage in order to use less
  energy and spend less money
• Prevent surprising power bills at the end of the
  month
• Corroborate energy savings of energy efficient
  appliances
• Make system user friendly

4
Project Overview

• Build a circuit to measure the current and
  voltage used by an appliance
• Make program to calculate power
• Program transceivers to communicate with each
  other
• Build circuit to display information on LCD
• Make program to display information

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Project Specifications

• No more than 5 accuracy error
• Wireless operation using Xbee wireless protocol
• Wireless transmission should be no less than 30
  feet
• Ability to turn off appliance from head unit
• Measure current up to 15 A
• Measure voltage up to 120 V

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Block Diagram of System
Current Measurement
Relay
Wall Outlet
Voltage Measurement
Microprocessor
Wireless transmission
Display
Microprocessor
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Meter Overview
Ryobi Power Meter- printed with permission from
Jason Swanson of Ryobi Tools
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Requirements

• Meter circuit should draw very little power
• Meter circuit design should be safe
• Achieve accuracy goals

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Power measuring methods

• Voltage measurement using a voltage divider
• Current measurement using a .2 ohm current
  sensing resistor
• Use an Avago technologies HCPL-7520 optoisolator
  to isolate and amplify the signal
• Use a relay to turn the appliance on and off

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Power Meter diagram
Relay Circuit Design Used by permission from
Bruce R Land, Cornell University
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Voltage measurement

• Voltage will be measured directly from the house
  main wiring
• A voltage divider will bring down the voltage to
  a level usable by the microprocessor

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Current measurement

• Current sensing resistor will be installed in the
  neutral side of the outlet wiring
• A hall effect sensor was considered but it is too
  expensive
• A current transformer was considered but it is a
  less accurate method and more expensive

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Component specifications

• 5 tolerance, 1 watt power rated 1Mohm resistor
• .2 ohm, 3W rated current measuring resistor
• 12A, 240V relay
• Avago Technologies HCPL-7520 linear optoisolator

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Limitations

• Meter cannot measure appliances that run on 240V
• Current to be measured cant be more than 15A

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LCD DISPLAY
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Proposed diagram of device
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LCD display requirements

• One row to list the information to identify what
  is display on the screen.
• Three rows of data pertaining to three separate
  sensor devices.
• Must have a traversable menu to view up to 1000
  different sensors.
• Must display power consumption data in terms of
  dollars spent.
• Simple character display method.
• LED backlight for nighttime use.
• Low power consumption. (lt 3W typical)
• Low price. (lt50)
• Readily available.

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LCD Specs Technical Data
NHD-0440WH-ATFH-JT

• 4 lines x 40 characters
• 2 - HD44780 equivalent microcontrollers
• 190mm x 54mm x13.6mm
• 18 - 2.54mm pins (14 Logic, 3 Supply, 1 NC)
• Requires a 5.0V Power Supply
• 11 Built-in instructions
• 5V, 1.2mA typical for LCD (.006W)
• 3.5V, 80mA typical for Backlight (.28W)

Reprinted with permission of Newhaven Display
International
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Limitations
Our Resolution

1. Include an LED on/off switch to conserve battery
   power
2. Place device high on wall so all users can view
   information
3. Put device in a central viewing location
4. Practice our soldering skills
5. Update data values every 60 seconds instead of
   continuously.
6. No solution, opt for microcontroller with more
   pins

1. With the LED on, it drains 48 times more energy
   then when it is off.
2. Viewing angle from above is only 25.
3. Poor horizontal viewing angle.
4. Small pin size.
5. Relatively slow rise and fall times.
6. Many pin outs

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Push Buttons/ Switches
Pushbutton Examples

• We require three tactile (push-to-make)
  pushbuttons on the front of device.
• Two of these buttons will be used for movement
  within the LCD menu.
• One pushbutton will disconnect supplied power to
  selected appliance.
• We also require a Single pole, single throw
  switch on the side of the device to control the
  LED backlight

Reprinted under creative commons 3.0 license
SPST Example
Reprinted with access from public domain
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User - LCD Interfacing

• LCD will be connected to pushbuttons via internal
  microcontroller.
• With microcontrollers coding, a cursor will move
  through the list of devices when up/down buttons
  are pressed.
• When the user continues pushing the up/down
  buttons to view more than the three listed
  devices, new devices will appear in their place
• When the user hits then end of the list of
  transmitting devices, the cursor will stop
  moving.
• A user can terminate the supplied power to the
  cursor selected device by pushing the power
  button.
• Pressing a combination of buttons will allow the
  user to enter a menu in order to set up the date
  and cost of electric bills.

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Instructions
Instruction List

• To operate, the device has 2 separate internal
  microcontrollers to display to the LCD.
• A specific instruction must be selected by the
  main microcontroller and sent to the eight data
  pins.
• When the instruction is sent, the device must be
  enabled on the selected microcontroller (E1 or
  E2) to have the device complete the instruction.
• If characters are to be displayed, the RS pin
  must be set on and the device will output the
  selected character to the specified location
  designated by the set address command

Reprinted with permission of Newhaven Display
International
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Coding
Coding example (Turning device on)

• The microcontroller uses C programming language,
  and the Newhaven Display provides libraries for
  use with their product.
• The code will start off with an initialization
  section for initial power up of device.
• Then the device will display the data every
  minute from the MC in a line by line fashion to
  ensure all sensors are updated.
• Separate functions will be called for cursor
  movement, menu setup, and sensor power down.

• Int main(void)
• P1 0x0c
• W 0
• RS 0
• E1 1 //Top half of the display
• delay(2)
• E1 0
• E2 1 //2nd half of the display
• delay(2)
• E2 0

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Block Diagram
Schematic
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Microprocessor Design
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Microprocessors

• One single type of microprocessor for both
  applications
• Both applications use ATMega168 with a preloaded
  bootloader.
• Programmed with a USB to serial adapter.
• 6 analog input pins
• 14 digital input/output pins
• 1.8 to 5.5 volt operating voltage
• Programmed with Arduino software v. 0018 using
  C/C
• Each pin draws up to 0.22W (from 40mA), VCC draws
  up to 0.275W (from 50mA)

Reprinted with permissions from Sparkfun
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Programming

• Main unit programming
• Initialize()
• double kwhrs
• int month, day
• Sets up initial parameters
• Can be called further down the program to change
  values put in initially.

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Programming

• Main unit programming
• update_lcd()
• int out0, out1, out2
• int power, scroll_up, scroll_down
• Used to update information printed to the LCD
  screen.
• Handles scrolling of information displayed and
  ability to turn off and on any given device

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Programming

• Sensing unit programming
• read_measures()
• int voltage_in, current_in, power
• Takes in all values read in by the sensing
  components
• Manipulates the data to be transmitted as a
  single value

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Programming

• Sensing unit programming
• change_relay()
• int relay_status
• Serves to open the relay to cut off all power to
  any given device

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Proposed Main Unit Schematic

• Receives power through batteries and bucked down
  to usable voltages.
• Pull down resistors to prevent button inputs
  from floating high.
• Schematic based on Arduino Pro Mini.

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Proposed Sensor Schematic

• Receives power through an AC to 5VDC converter
  (not shown)
• Transistor used to flip the relay as it uses
  more current than the processor can output.
• Based on the Arduino Pro Mini

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Wireless Communication
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Wireless Telecommunications

• There were four types of wireless technology that
  were taken into consideration.
• Zigbee Cheap, Good distance, Hard to learn
• Bluetooth High data rate, Great delivery
  percentage, Hard to learn
• WiFi Great delivery percentage, Expensive
• XBee Easy to learn, Cheap, Good distance

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XBEE
Of the many possible options, we chose XBee
technology as our means of wireless
telecommunications.
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XBee Chip

• XBee OEM RF 802.15.4
• The range was good enough for the group having a
  max range of 100ft (30m)
• 24.38mm x 27.61mm

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XBee Specs

• The XBee costs 19.00 per unit.
• 250kbps might seem small for a commercial product
  but for a simple project, like the power sensors
  and the central unit, it will be sufficient to
  work properly.
• It is an RF transceiver. It runs at 2.4 GHz,
  which is what all the devices run at that the
  group has examined.
• Voltage range from 2.8 to 3.4V.
• The current
• when it is receiving data is 50mA,
• while it is transmitting information, the current
  is flowing at 45mA
• and while it is in power-down mode it runs below
  10µA.
• Its sensitivity is at -92dBm.
• The chips operating temperature has a range
  between -40 and 85C

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XBee Adapter

• 10/kit
• Connects to microcontroller
• Cord connects to computer to program the chip

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Programming of XBee

• Using the AT command mode is the how the XBee
  chip will be programmed.
• AT commands deal with all things from setting the
  sleep mode to resetting the chip.
• The command below is a sample command will
  display the low 32 bits of the address.

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Block Diagram of XBee
How data is received from one device and then sent to another device
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Timeline, Budget and Completion Summary
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Timeline
Our timeline for Senior Design was based on
bi-monthly goals.
April 30th Complete Research Documentation May
31st Have good understanding of all of our
parts June 17th All parts tested July 1st Have
all parts put together July 15th All parts
tested and working, also giving us two weeks to
figure out any problems and preparing ourselves
ready for presentation
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Approximate Budget
Required Acquired Estimated () Spent ()
LCD 1 1 24 35
Arduino 0 3 100 100
Relay 3 5 5 20
Arduino Programmer 2 2 0 40
AC/DC converter 3 4 15 20
Current Sensing Resistor 3 5 6 9
Optocoupler 6 5 40 30
PIC microprocessor 3 5 20 30
Xbee transceiver 5 2 300 120
Xbee Cords 1 0 15 0
Pushbuttons 3 0 6 0
Switch 1 0 5 0
Project Box 4 0 15 0
RLC ? 0 30 0
TOTAL 35 32 581 404
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Completion Summary
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Questions?