Batteryless Io T Devices BatteryLess Io T Device
Battery-less Io. T Devices Battery-Less Io. T Device SD-DEC 19 Team 21 Advisor: Dr. Henry Duwe Clients: Dr. Nathan Neihart Dr. Daji Qaio http: //sddec 19 -21. sd. ece. iastate. edu/
Member Contributions ● ● ● Antenna design and testing ○ Matt & Mohamed G Power System & Rectifier design and testing ○ Derek & Adi Microcontroller functionality, communications, and testing ○ Mohammed Al-Mukhaini & Brad Website design/maintenance ○ Mohammed Al-Mukhaini & Derek Documentation ○ All members Outreach/ meeting coordination ○ Mohammed Al-Mukhaini
PROJECT PLAN
Problem Statement ● General Problem statement: ○ Harvest RF energy and convert it into a form useable by a microcontroller ● General Solution Approach: ○ Harvest and convert ambient RF waves into DC ○ ○ Gradual charge and storage (capacitor) Low Power Mode Microcontroller
Conceptual Sketch
Functional Requirements Energy Harvesting ● Harvest RF signal from Wi. Fi router Power ● Long term low voltage storage ● Regulated Voltage supply to microcontroller Rectifier ● Rectified & Multiplied voltage ≥ 1. 8 V Embedded Systems ● MSP 430 microcontroller ● Record temperature via internal ADC ● Store and transmit data at a later time
Non-functional Requirements ● Portability ○ ○ ● Efficiency ○ ● Reasonable operation and charging time Testability ○ ● Prototype reasonable size Compatible Reliable for demonstration Reasonable cost ○ Under $100
Market Survey ● ● ● Not many other manufacturers Powerspot kit ○ www. powercastco. com ○ Focused on harvesting ○ Not communicating HUGE potential ○ Network of batteryless devices ○ Self-sustaining ○ Remotely located ○ Dependable
Potential Risks Device Safety ● ESD ● Fall height Financial Safety ● Unfeasible to implement ● Parts are too expensive Public Safety ● Device is above head height ● Touching may induce a shock
Resource Estimate Cost Reference No. Item Cost Per Unit x Number of Units Total Cost 1 Skyworks Schottky Diodes: SC-79 $0. 85 x 4 $3. 40 2 Capacitors (Mouser Electronics) $0. 14 x 4 $0. 56 3 MSP 430 FR 5994 $20 x 1 $20. 00 4 TE SMA Female connectors $2. 49 x 3 $7. 47 5 Fabrication of antenna PCB $5. 00 / in 2 * 4 $20. 00 6 Fabrication of rectifier on a PCB $5. 00 / in 2 * 3 $15. 00 Total $66. 43
SYSTEM DESIGN
Functional Modules
Antenna Circuit Platforms ● Patch Antenna radiating at 2. 4 GHz ● Easy to manufacture, low-profile ● Generating low power ● Moderate antenna efficiency Figure 01: 2. 4 GHz Patch Antenna
Antenna Circuit- Simulation ● Simulation, tuning, and validation done through HFSS ● d. B gain values, radiation pattern and S parameters
Power Circuit Platforms ● ● Cockcroft-Walton Voltage Multiplier (CW) Rectify & Multiply 2 Stage multiplier Primary Component ○ Figure 04: Schematic of CW voltage multiplier Schottky diode (Skyworks Schottky Diode SC-79) ■ Low forward voltage drop ■ Negligible leakage current Figure 5: PCB design of CW voltage multiplier
Power Circuit- Simulation ● Using ADS (Advanced Design Systems) ● Tests include: S-parameter, transient, and harmonic balance Figure 06: Rectifier circuit simulation Figure 07: Rectifier Schematic on ADS
Embedded Systems Platforms (MSP 430 FR 2100) ● MSP 430 FR 2100 MCU ○ Voltage Range: 1. 8 v - 3. 6 v ● Low Power Modes ○ Different current supply demand ● System clock up to 16 MHz ● FRAM - 1 KB ○ Unified memory program, constants, and storage ● 10 -bit ADC ● Integrated UART functionality
Embedded Systems- Testing and Simulation ● MSP-EXP 430 FR 5994 ● Code Composer Studio ● Energia Current Developments ● Temperature data recorded and stored in FRAM ● Previously recorded data is not overwritten ● Display and measure energy profile
Building Block Implementations Figure 8: Hardware flow Implementation Figure 9: Software flow control Implementation
CONCLUSION
Project Milestones & Schedule ● ● ● MCU code working on development board - May 2019 Rectifier circuit built - Mid September 2019 Energy harvesting circuit built - October 2019 Prototype board assembled - October 2019 - early December 2019 Final product assembled - Mid December 2019
Current Status
Plan for next semester ● Finalize software and flash code onto FR 2100 MCU ● Incremental tests, culminating in full test ● Delivery of final product
QUESTIONS?
Energy Storage - Capacitor ● Capacitor to store charge ○ ○ ○ Power demand ■ X = 1. 8 V = min voltage for MSP 430 ■ W = ideal steady operation power (watts) ■ t = operating time ■ Vs = starting voltage (output of rectifier) VC = Vs * e-t / (RC) ■ W = X 2 / R => R = W / X 2 VC = Vs * e(-t*X^2) / (WC) X ≤ Vs * e(-t*X^2) / (WC) With all other variables found, solve for C
Justification - Rectifier V 0 = 2 n. VMAX - �V 0 Ideally, �V 0 = 0. But due to not-fully-charged capacitors, we have: Larger C = smaller �V 0 loss Proof: https: //www. hindawi. com/journals/jece/2017/4805268/ (plan to test with several different types of capacitors empirically)
Justification- Schottky Diodes ● No depletion region → low forward voltage drop ○ Electrons present on both sides of the junction ● Current conduction due to electron movement only → negligible leakage current ● No reverse recovery time ○ Instantaneous switching action
MSP 430 Energy Consumption ● Current draw drops rapidly when switching to lower power modes ● Efficiency increases when operating at higher frequencies and lower voltages
FR 4 Parasitics Calculation ● Capacitance Parasitics ● Trace Inductance Parasitics ● Inductance Parasitics
Potential Risks Device Safety ● ESD ● Fall height Financial Safety ● Unfeasible to implement ● Parts are too expensive Headache Electric Shock Public Safety ● Device is above head height ● Touching may induce a shock Electrostatic Discharge Short Circuit LOW RISK FACTOR
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