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NETWORKED DC/AC POWER MONITOR
Freescale – Thread IoT
GROUP 2.4
ALAN H HENDERSON
BRIAN SAMUELS
LAHCEN BOUHOU
KELSEY KING
SAMUEL CHABOT
PROJECT MANAGER
HARDWARE ENGINEER
HARDWARE ENGINEER
SOFTWARE ENGINEER
SOFTWARE ENGINEER
Project Description
Goal: Design a networked solution to monitor AC and DC power for use on the solar
panel and wind turbine setup for the SMART Lab
Scope: Design and implement a prototype
• Flexibility to sense AC and DC voltage and current experienced in the SMART Lab
• Data transmission using Thread network
• Power Management
Stretch Goals
• Design a minimal PCB layout
• Deploy a full scale network
• GUI to analyze power production in the SMART lab
SMART Lab Schematic
• Flexible design to account for all
SMART Lab devices
6750 W System
• 87 locations for sensors
o 53 solar panels
o 9 wind turbines
o 18 8D sealed lead-acid storage
batteries
o 7 DC/AC inverters
• Each will measure voltage and current
o 174 signals to transmit via
Thread
Three 1520 W Systems
Design Constraints
• Versatile design for universal pairing with
various SMART Lab elements
o Solar panels
o Wind turbines
o Batteries
o Inverters
• IEEE 802.15.4 compatibility required
• Lowest possible cost due to future mass
production
• Weather-proofing
• Sense DC/AC voltage:
o Voltage range between 0V-300V max
o Resolution has to be 0.1 V
o Sample Frequency 1Hz
o Batch frequency between 1to 10 min
• Sense DC/AC current:
o The current range between 0A -150 A max
o Resolution has to be 0.05A
o Sample Frequency 1Hz
o Batch frequency between 1to 10 min
Hardware Design Details: Sensing
• The sensing circuits can measure AC and DC
voltages and currents
o 3 phase AC
o Frequency will be measured via a zero crossing
strategy at the software level
o Phase angle can also be measured and will also
occur at the software level
• Voltage sensing via a voltage division resistive
network and an operational amplifier
o Large resistances to limit current
• Current sensing utilizes a ACS759KCB-150B-PFF-T
hall effect IC
o This device is rated to read ±150A bidirectional
o Outputs 0 to 3.3V, where -150A equals 0V and
+150A equals 3.3V
Hardware Design Details: Power
• Power will initially be provided via a battery pack but
parasitic power is being pursued.
o On a board level using another resistive network and a
voltage regulation circuit. This will result in significantly
increased costs and a more complicated PCB.
o A single DC source connected to the main battery pack
for the entire solar and wind power array. This will be
easier but it will also entail routing low voltage DC
wires back out to every sensor. This negates some of
the benefits of having a wireless system.
Hardware Solution
•Circuit required to both reduce and
offset the voltage to a range of 0 to 3.3V.
•Figure shows utilization of operational
amplifier with negative feedback loop
•A voltage divider used to reduce
onboard power supply to offset the
voltage to the desired range of 0 to 3.3V.
Validation Test Plan
The following cases are tested using the KW24D512-TWR board as a prototype:
Sense DC/AC voltage:
•Voltage range between 0V-300V max
•Resolution has to be 0.1V
•Sample Frequency 1Hz
•Batch frequency between 1 to 10 min
Sense DC/AC current:
•The current range between 0A -150A max
•Resolution has to be 0.05A
•Sample Frequency 1Hz
•Batch frequency between 1 to 10 min
Data Transmission verified using Proximetry Agent
Thread Network
• Thread group established in July 2014
• IPv6-based
• Self-healing mesh networking protocol
• IEEE 802.15.4 standard transmission hardware
compatible
• Support for up to 250 devices
• Texas State University Thread network deployed
April 2015
• Thread updates scheduled will include capability
to transmit multiple data types
Proximetry Agent
• Web-based interface coupled with Thread
• Displays real-time network information
o Routers
o Devices
o Access points
o Status of nodes
• Responsible for receiving and charting
transmitted data
• Secure, location-independent access via web
login
Proximetry Data Monitoring
• Real-time data view
• Time axis expandable from five
minutes to one week
• Multiple users able to concurrently
view data
• Future updates will allow for data
types to be displayed at once
Prototype Budget
Project Name
Project Section
Company
Cost Each
Cost Total
Cost 500
DC Voltage
Voltage Divider
3
10
Vishay/Mouser
$0.19
$1.90
$0.125
Voltage Divider
3
10
Vishay/Mouser
$0.12
$1.20
$0.120
Voltage Divider
6
10
Vishay/Mouser
$0.19
$1.90
Operational Amplifier
3
5
Mouser
$0.58
$2.90
Input Resistor
3
5
Mouser
$0.26
$1.30
Feedback Resistor
3
5
Mouser
$0.69
$3.45
Current Transducer
3
3
Digi-Key
$7.98
$23.94
10uF Capacitor
1
2
Mouser
$0.56
$1.12
0.1uF Capacitor
1
2
Mouser
$0.30
$0.60
$0.340
Circuit Protection
3.3V Zener Diodes
14
14
Mouser
$0.34
$4.76
$0.250
Freescale Tower
Development Board
1
1
Freescale
$149.00
(Donated)
$0.188
Elevator Module
1
1
Freescale
$39.00
(Donated)
$0.000
AC Voltage
Required
Total (with spares)
$0.190
$0.266
$0.180
AC/DC Current
Total: $43.07
$0.179
$4.200
$6.07
Impact
• Our solution provides a wireless
flexible data collection tool:
o AC/DC
o Current/Voltage
o Wide ranges
• Monitor the Efficiency of the
SMART Lab
• Other Possible Applications:
o DC grid data collection and
evaluation
• Safety:
o High voltages and currents
• Ethical:
o With the evolution of
connected devices, security
becomes an inherent concern
•Environmental:
o Low power characteristics
mean efficient operation
o Materials can be sourced
environmentally-friendly
Future Plans
• New iterations of the Thread networking protocol
o multiple data types
o generated software hooks/constructed hardware
- 3-phase AC voltage, current, and power
- Minimal PCB layout can be expanded upon
- Prototype can be duplicated and deployed across the desired
87 locations in the SMART Lab to take full advantage of the
power monitoring solution.