Levitating LED Light

Levitating LED Light
ECE4007 Senior Design Final Project Report
Section L03-04, Team L3
Project Advisor, Prof. Maxwell, Prof. Koblasz
Harold Kimball, Team Leader
Chris Melton
Andy Givens
ShrutiBatra
Inga Shvartsman
Submitted
December 16, 2010
Table of Contents
Executive Summary .......................................................................................................... ii
1. Introduction ..................................................................................................................1
1.1
1.2
Objective .............................................................................................................1
Motivation ...........................................................................................................1
2. Project Description and Goals ....................................................................................2
3. Technical Specification ................................................................................................3
4. Design Approach and Details
4.1
4.2
Design Details .......................................................................................................4
Codes and Standards ...........................................................................................13
5. Schedule, Tasks, and Milestones ..............................................................................13
6. Results and Acceptance Testing ...............................................................................14
7. Budget and Cost Analysis..........................................................................................16
8. Conclusions and Future Work..................................................................................18
9. References ...................................................................................................................21
Appendix A .......................................................................................................................22
L3 (ECE4007L03-­‐04) i Executive Summary
The levitating LED Light is a lit orb that levitates in air and allows its users to wirelessly
illuminate their households, offices, classrooms, restaurants, bars etc. The L3 was created as a
teaching tool that incorporated core concepts from Electrical Engineering courses such as
Electromagnetics, Power and Controls Systems, and could be sold to Engineering schools. Its
function is based on the principles of electromagnetic induction wherein a circular piece of wire
attached to a rare earth (Neodymium) magnet is suspended in a magnetic field using a magnetic
coil above the ball controlled by a current regulating feedback loop using Hall Effect sensors.
Attached to the coil will be LED lights powered by a second coil above the ball feeding a time
varying flux to a “receiving” coil inside the floating ball. The current is rectified and usedas
power by the LEDs. This project is envisioned as a subsystem of a larger device that can
manually adjust the levitation height and luminosity of the orb as well as react to a music input
signal. It successfully performs the proposed functions of wireless illumination and magnetic
levitation. L3 is priced at $120 but replaces the household bulb with a new light source that can
wirelessly be placed anywhere in the house and turned on and off at will. L3 will primarily be
marketed to Engineering Schools and Science education camps in order to attract current and
aspiring students to pursue Electrical Engineering courses.
L3 competes with products in the market that allow a user to levitate basic objects such as a globe
or a light frame, but these products don’t have the ability to illuminate their surroundings. The
Galileo Gravitator Lamp and Crealevs edition of magnetically levitating devices are examples of
products that could potentially compete with L3.
L3 (ECE4007L03-­‐04) ii 1. Introduction
Project engineers spent $120 to design and prototype the L3 that magnetically levitates in air and
illuminates 6 LEDs.
1.1 Objective
The L 3 (Levitating LED Light) is a glowing object that levitates in air under the influence of
electromagnetic radiation. The L3 consists of a floating object, dubbed the “orb”, which has LED
lights attached to it. The flotation and illumination functions can operate independently or
together. This orb has the ability to float 2-2.25 inches below a control box, which may be placed
in or attached to the ceiling.
The L3 is priced at $120 and will primarily be sold to engineering schools in the United States.
The vision was to create a teaching tool that helped students better understand the concepts of
Electromagnetics, Power and Controls Systems and how the three topics are interrelated. A
similar device, the Galileo Gravitator Lamp, consists of a levitating globe used to accessorize
households and to visually demonstrate the basic concepts of magnetism to middle school
students. Although the Galileo Gravitator Lamp priced at $81.99, is $38.01 less than L3, it does
not have the ability to light up in a magnetic field.
1.2 Motivation
L3 will cost $120, versus the Gravitator Lamp at $81.99, though we wish to improve on this
design by creating a greater luminosity, levitation distance and the additional application of
vertical movement to music as well as extensive safety measures. The above mentioned technical
features are mentioned in detail with their respective mathematical values in the technical
specifications section. The L3 still needs to meet all building codes and necessary requirements
L3 (ECE4007L03-­‐04) 1 for safe installation as well as comply with FCC constraints. A “fail safe” is included; in the
event of a power loss, the magnetic pull of the Neodymium magnet will take over and pull the
entire floating orb towards the control box instead of dropping it on patrons below.
This task was done in order to demonstrate a task as trivial as providing light in a way that
emphasizes wireless control of the amount of light shining andlevitation height. The L3 has a
higher MSRP than its competitors because it should be able to meet all building codes [2] and
necessary requirements for the safe installation in university labs. The use of the L3 as a teaching
tool in engineering schools essentially summarizes our motivation for this project.
2. Project Description and Goals
The L3 magnetically levitates and wirelessly transfers power to a LED fixture. Out of the
goals that were proposed for the L3, namely
•
Magnetic levitation of LED fixture
•
Wirelessly transfer power to LED fixture for illumination
•
Move up and down to the base from an audio signal
•
Plug directly into 120 VAC electrical outlet for power
•
Lightweight, durable PVC frame
We successfully completed 4 out of the 5 design requirements. The first task to be completed
was calculating the design requirements for the wireless and levitation circuits. Second, we
successfully illuminated 6 LEDs with moderate intensity and 4 LEDs with bright blinding like
intensity. Third, we created the levitation coil and the strength of the electromagnet was
constantly adjusted using of 2 Hall Effect sensors through a feedback control system. The
vertical displacement of the LED fixture requires a mixer in order to filter out the base/kick drum
L3 (ECE4007L03-­‐04) 2 signal from the output of an iPod. Moreover, we attempted to simulate the bouncing movement
by turning the LEDs on and off and that resulted in the system becoming critically unstable. The
target users for the L3 are professors and research students who need teaching aids in order to
demonstrate the concepts of Electromagnetics and Power systems.
3. Technical Specifications
Overall, the project performs as expected. The levitation distance, which was one of the main
goals, was accomplished at a distance of 2.25 inches. Also completed was the task of
illuminating 4-6 LEDs with wireless power transfer. The lift mode was switched from repulsion
to attraction in order to provide greater stability and levitation distance. The orb has levitated in
lab conditions for 45 consecutive minutes before the core gets too hot. Table 1 gives the
specifications of the project, separating what was proposed from what was accomplished.
Table 1. Comparison of Proposed Project Specifications to Implementation Spec
Proposal
Implementation
Levitation Distance
Plastic Orb
Electromagnet
2-3 in
2-3 in
4 in diameter
500 turns
18 AWG
Repulsion
10 in diameter
100 turns
14 AWG
Music Reactive Functionality
2.25 in
3 in (no surrounding sphere)
3 in in diameter
900 turns
24 AWG
Attraction
5 in diameter
20 turns
24 AWG
No
Lift Mode
Antenna
Bouncing
L3 (ECE4007L03-­‐04) 3 4. Design Approach and Details
4.1 Design Approach
Antenna and Receiver
The two antennae used in the L3 function as inductively coupled current loops. For calculation
purposes, the antennae can be viewed as an axially coupled, air-core transformer. Figure 1shows
the model used to attain the design parameters.
Figure 1. Power transmission antenna modeled as axially
coupled air core transformer.
L3 (ECE4007L03-­‐04) 4 Using the reluctance of the air-core circuit, and the magneto motive force from the current
oscillator (discussed in 4.2), the flux produced by the driving antenna is approximated by
Equation 1.
Equation 1. Flux produced by drive antenna.
Assuming all flux is transferred to the receiving coil, we model the voltage in the receiving coil
with Equation 2.
Equation 2.Receiver coil voltage.
Table 2 summarizes the input parameters and results of the calculations. To power the LEDs, we
required at least the 1.5volt turn on voltage. This set a minimum requirement for current through
the oscillator at roughly .2 amps.
Table 2. Input Parameters and Calculation Results for Receiver Coil Voltage
Description
Symbol
Value
Transmitting No. of Turns
N1
20
Receiving No. of Turns
N2
20
Peak Current through Transistor
Permeability Constant
I
µ0
.2 Amps
4π*10-7 H/m
Area of Receiving Coil
A2
π(3.8)2 cm
Distance of Levitation
l
6.5 cm
L3 (ECE4007L03-­‐04) 5 In order to reduce the impedance of the transfer capacitors were placed in parallel with each
antenna and matched to the transfer frequency using the equation
. The oscillator circuit
(described later) sets restrictions, which led us to the 100kHz transfer frequency used.
Antenna Driver Circuit
The L3 uses a variant of a Royer Oscillator, shown in Figure 2, to drive the impedance matched
antenna discussed in Section 4.1. It is powered by a HP 3630 A DC power supply from the +15
volt rail. Its maximum output (measured across the LC Tank) was 80Vpp. The components and
their ratings are listed in Table 3. Of special consideration is the LC Tank consisting of C1 and
L2, Switch J1, and inductors L1 and L4. The 37.2 µH inductor L2 represents the transmission
antenna and will vary with differing antenna designs. The parallel combination of C1 and L2 are
resonant at a frequency defined by
. This is also the transmission frequency of the
antenna. It can be adjusted by changing the value of C1. The L3 uses 5 1000V 6.8nF capacitors
in parallel and a 74.5µH antenna yielding a transmission frequency of approximately 100KHz.
Switch J1 is a single pole single throw switch used as an under voltage lockout. It basically
allows the power supply to reach full voltage and current sourcing levels before turning the
oscillator on. It can be replaced with a relay if direct control of the antenna is undesired. If the
switch is shorted at startup, the mosfets turn on too fast and do not allow the transient sine wave
to build up on the LC Tank providing a DC short to ground through the mosfets. Inductors L1
and L4 are shorts at DC for mosfet biasing purposes while open at AC preventing feedback to
the power supply when the LC Tank swings above 15V. More in depth analysis of the circuit can
be found at http://4hv.org/e107_plugins/forum/forum_viewtopic.php?74096.
L3 (ECE4007L03-­‐04) 6 Figure 2. Royer oscillator used to drive power transmission antenna.
Table 3.Oscillator Components and Relevant Specifications.
Component Part Name Rating (V, I, W) R1, R2 N/A 1 W R5, R6 N/A ¼ W Q1, Q2 IRFZ44N 55V, 49A D1, D2 1N4148 N/A L1, L4 N/A 14A C1 WIMA FKP1 1000V L3 (ECE4007L03-­‐04) 7 Levitation Coil
The levitating coil is the electromagnet responsible for providing the lifting force for the orb. The
iron core used is approximately 6 cm in diameter and is wrapped with 800 turns of 24 AWG
magnet wire. This wire provides minimal insulation thickness to allow the coils to be tightly
packed around core. The fringing effects of the B-field create difficulties in determining the
lifting force provided, but a rough estimation was calculated using Equation 3.
Equation 3.Lifting force of electromagnet.
Equation 3 estimates the lifting force directly below the magnet, but without contact. The field
strength falls off in the near field with the cube of the distance (cm), which gives an estimated
35.9 grams of lifting force. Using superposition, the lifting force from the Neodymium magnet,
which is roughly 13.6 grams according to the manufacturer’s website, can be added to the other
lifting action for total lifting force of 50 grams. Solving this backwards allowed us to determine
the number of turns, N, the lifting coils needs.
Feedback Control Circuit
The control system is powered by a HP E3630 A DC power supply with outputs set to 5V, 15V,
and -15V. All op-amps are powered by the +/-15 volt rails while the Hall Effect sensor operates
on the 5V rail. The levitation coil is powered by a GPR-6030D 60V 5A power supply set to 23V.
Both supplies are forced to share a common ground by connecting the negative rail of the GPR 6030D supply to the ground rail of the HP E3630 A.
L3 (ECE4007L03-­‐04) 8 The feedback control system on the L3 is based around two AD22151YR linear magnetic Hall
Effect sensors shown in Figure 3. By adjusting R2 and R3 the gain can be adjusted according to
the formula
and is set to 5 in the L3 using 1/4W 82KΩ and 8.2KΩ
resistors. R1 is open.
Figure 3. AD22151YR Linear Hall Effect Sensor reference pin out.
The feedback control diagram will be presented in two parts. The first, shown in Figure 4, has
the two Hall Effect sensors modeled as DC voltage sources set to 3V (the parts are not specified
in Multisim). The second is part is shown in Figure 5. Nominal voltages for two circuit testing
conditions are provided at the end of the section in Table 4.
Part A of the controls consists of two low pass filters with a cutoff frequency of 10Hz. These are
used to filter noise out of the control circuit induced by the power transmission antenna. Since
the antenna operates at 100 KHz, the interference is attenuated by 80dB.
L3 (ECE4007L03-­‐04) 9 Part B consists or two op-amp voltage follower or buffer circuits. The lower buffer is necessary
since R7, R8 and R2 provide an additional path to ground and will shift the response of the low
pass filter in part A. The upper buffer is added so that signals from both sensors will experience
similar delays.
Part C is a single stage unity gain differential amplifier. Potentiometer R2 is used to tune the
circuit such that the maximum CMRR is achieved. The bottom sensor (which will have the flux
through it reduced by the neodymium magnet in the orb) is fed into the positive terminal of the
op-amp resulting in a negative change in voltage when the orb is present.
Part D is an adjustable non-inverting gain stage. Its gain ranges from 2 to 101. It is used to scale
the negative voltage change created in part C to a useable level. With the orb present, the output
was set to approximately 3V.
Figure 4. Feedback control loop part 1. All op-amps are TLO71s or 741s.
Part E, seen in Figure 5, is an adjustable voltage divider used to set the reference for the
summing amplifier which follows. In the absence of the orb this sets the gate voltage for the
mosfet in part I to 9V.
L3 (ECE4007L03-­‐04) 10 Part F is a unity gain summing amplifier using four 1% 5KΩ resisters to reduce bias toward a
single input. When the orb is absent, it acts as a unity gain buffer for part E. When the orb is
present it adds the negative voltage from part D to the reference set in part E. This results in a
gate voltage of approximately 6V.
Part G is a phase lead filter, also known as a proportional integration (PI) controller. The Hall
Effect sensors provide only positional information about the orb. Once the control system begins
to act it moves the orb, introducing a new and significant speed variable to the system which
cannot be accounted for. Using the PI controller, the present position information is combined
with data on the previous position stored in the capacitor C3. This allows the speed to be inferred
and controlled. Adjusting the component values adjusts the position and speed coefficients
allowing it to be tuned.
Part H is another adjustable gain stage. It compensates for the 1/101 voltage divider in part G and
is adjustable to accommodate tuning of the PI controller.
Part I shows how the control circuit interfaces with the levitation coil. The control circuit adjusts
the gate voltage on Q1, which changes the coil current. The inductor L1 represents the levitation
coil. Its value is not 1MH; this was used as a placeholder since the simulations results are not
useful for feedback analysis and its value will need to be changed if the coil is changed.
L3 (ECE4007L03-­‐04) 11 Figure 5.Feedback control loop part 2. All op-amps are TLO71s or 741s.
Table 4. Nominal Voltages for Control System without orb and with Coil Power On and Off
Circuit Stage
Voltage (Coil off)
Voltage (Coil On)
Oscilloscope Scale
(Part Letter)
V
V
Hall Top (A)
3
1.5
5V
Hall Bottom (A)
3
1.4
5V
LPF Top (A)
2.8
1.4
5V
LPF Bottom (A)
2.8
1.3
5V
Buffer Top (B)
3
1.5
5V
Buffer Bottom (B)
3
1.4
5V
Diff Amp (C)
.001
.011
50mV
Gain (D)
-.007
-.142
50mV
Divider Reference (E)
8.4
8.3
5V
Summer (F)
9
8.1
5V
Lead Filter (G)
.6
.7
5V
Gate Bias (H or I)
8.7
7.1
5V
L3 (ECE4007L03-­‐04) 12 4.2 Codes and Standards
The L3 was not designed to comply with IEEE or FCC guidelines regarding radiated emissions
and is currently in violation of these standards.
(http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf)
5. Schedules, Tasks, and Milestones
The L3 device was designed to implement and demonstrate the bolded major tasks and the
italicized milestones shown in Table 5.
After the completion of the Levitation circuit, the LED Illumination circuit, we combined the
two individual designs together. The AC power input needed to be sufficient for both and the
circuitry designs required to be integrated with one another. The Vertical Motion Task was not
accomplished due to a lack in funding.
L3 (ECE4007L03-­‐04) 13 Table 5. Scheduled Tasks and Milestones
Completed?
Proposed Milestones and Tasks
yes
no
Calculations
Power Requirements
Design Targets
LED Illumination
Ability to Power 6 LEDs
Impedance Matching
Signal Generation
Levitation
Two Inches from Coil
Circuitry Design
Vertical Oscillation
Music Filtering
Orb Momentum and Balancing
6. Results and Acceptance Testing
6.1 Levitation
The L3 achieves a levitation distance of 2.25” with the lights on and 2.00” with the lights
off. These distances are measured from the bottom face of the electromagnet to the top face of
the neodymium magnet on the orb using a wooden ruler. Figure 6 illustrates the levitation
distance measuring process that was used for acceptance testing.
L3 (ECE4007L03-­‐04) 14 Figure 6.Measuring the levitation distance with the lights on.
6.2 Wireless Power Transfer
The L3 uses two magnetically-coupled coils to wirelessly transfer power from its base to
the levitating orb in order to power 4-6 LEDs. All of the LEDs are connected in parallel with
alternating polarities. This allows for both the positive and negative half-cycle of the voltage
induced into the coil attached to the orb to be utilized for LED power, which was tested by
turning the room lights off and placing LED pairs into the levitating orb. Using low power, high
luminosity LEDs provided by Cree, illumination of 6 LEDs was achieved at medium intensity.
Four LEDs can be powered with high intensity as seen by the camera optics being saturated by
the four LED demonstration in Figure 6 above.
6.3 Vertical Oscillation
In the early development stages, a bouncing function was to be implemented in to the L3
in which the orb moved up and down to the kick drum component of an audio input signal.
L3 (ECE4007L03-­‐04) 15 Though experimentation with various low-pass filter designs, it was discovered that in order to
obtain a usable control signal from the bass a sound mixer would be needed. This would have
driven the project over budget and over time constraints so this feature was not implemented.
7. Marketing and Cost Analysis
7.1 Marketing Analysis
The L3’s target market is in the education realm. It may be used to exhibit and demonstrate
electromagnetic fields and wireless power transfer in the form of a teaching tool. An additional
smaller market includes individuals who are interested in illuminating their household in a
“different” way.
The Fascinations Corporation sells a variety of magnetically levitating globes that are able spin
in place. Their price range begins at $40 for a 4 inch, non-rotating globe and $100 for an 8 inch
rotating model. The L3 distinguishes itself by providing light.
7.2 Cost Analysis
The total cost for the L3 prototype was $36,862. At market price, the materials cost $69.69 and
the labor cost was approximately $36,792. Because many of the required materials were
procured without cost to the company, only $47.77 was spent. For the future, buying the
materials in bulk will result in a cost cut to $21. Table 6 illustrates the material cost breakdown
of the L3.
L3 (ECE4007L03-­‐04) 16 Table 6. Material Cost Breakdown of the L3
Part
Details
NMOS Transistor
IRFZ 44N
3
$5.04
Op-Amp
TL071
6
$1.50
Potentiometer
100 KΩ
2
$2.00
Potentiometer
10 KΩ
1
$1.00
Potentiometer
100 Ω
1
$1.00
Resistor
5 KΩ, 1%
4
$1.40
Resistor
Assorted, 5%
17
$0.85
Resistor
100 Ω, 1 W
2
$2.98
$2.98
Capacitor
6.8 nF, 1 KV
5
$5.00
$5.00
Capacitor
0.22 uF
2
$0.40
Capacitor
0.15 uF
1
$0.20
Hall Effect Sensors
AD22151
2
$11.02
$11.02
Magna Wire
500 ft
1
$9.65
$9.65
Diode
1N4148
2
$0.40
Inductor
100 uH, 14 A
2
$19.12
Cree LEDs
C535A-WJN
6
$2.58
Oscillator “On” LED
C503B-BCN
1
$0.55
1
$5.00
Steel Core
Total Build Cost:
Amount Market Cost
$69.69
Our Cost
$19.12
$47.77
L3 (ECE4007L03-­‐04) 17 In accordance to http://www.bls.gov/k12/math02.htm, the labor costs were paid by an hourly rate of
$42/hour; 99.8 percent of the project’s cost is in labor as shown in Table 7.
Table 7. Total Project Costs
Project Component
Class
Levitation
Controls
Power Transfer
Documentation
Total Labor
Total Parts
Total Overhead
Total Project
Labor Hours
120
132
132
132
360
876
Labor Cost
5040
5544
5544
5544
15120
36,792
Material Cost
37
56
(with controls)
5
Total Section Cost
5040
5581
5600
5544
15120
48
9198
36792
Table 4. Total Project Costs 8. Conclusions and Future Work
The L3 is currently a prototype that successfully levitates its orb 2.00 - 2.25 inches below the
Project Component Labor Hours
Labor Cost Material Cost Total Section Cost
Class
120
electromagnet and illuminates 4 - 6 LED’s5040
on the orb via wireless power5040
transfer. Figure 7 is a
Levitation
132
5544
37
5581
Controls
132
5544
56
5600
picture
of the working prototype.
Power Transfer
132
5544
(with controls) 5544
Documentation
360
15120
5
15120
Total Labor
876
36,792
Total Parts
48
Total Overhead
9198
Total Project
36792
L3 (ECE4007L03-­‐04) 18 Figure 7.Photograph of final working prototype.
The initial goals in developing the L3 were to design it to levitate an orb a distance of 2.00 – 3.00
inches, wirelessly transfer power to the orb to illuminate LEDs mounted on it, and have the orb
bounce up and down to the bass or kick drum of an audio signal while levitating and illuminated.
The levitation and the wireless power transfer goals were successfully reached, however due to
time and budget constraints the L3 cannot bounce to the bass of an audio signal.
The initial
motivation in designing the L3 was to market it as a novelty item that is an alternate way to
illuminate a small desk-sized area and/or a permanent lighting fixture in nightclubs. As the
project progressed, it was found (through great interest shown by ECE professors) that the L3 is
more marketable as a tool for electrical engineering schools to showcase concepts learned in
electromagnetics, electronics, power, and controls courses.
Since the L3 is just a prototype/proof-of-concept, it is not ready for production. While the linear
magnetic Hall-effect sensors used in this prototype worked in the end, their inconsistent
L3 (ECE4007L03-­‐04) 19 responses caused numerous problems, thus another prototype cycle should be initiated using
better ones. Recommendations for future work on the L3 include the following:
•
Implement the bouncing-to-music function
•
Redesign orb aesthetics
•
Construct a permanent stand/housing to support the electromagnet and coils and house all
circuitry
•
Consolidate the three power supplies to one or design a custom power supply
•
Complete antenna redesign or shielding to meet FCC regulations on RF emissions
•
PCB design
•
Design a single coil that provides adequate levitation and power transfer functions
L3 (ECE4007L03-­‐04) 20 9. References
[1] Coil Gun. (2008). Other Maglev [Online]. Available:
http://www.coilgun.info/levitation/other_maglev.htm [Accessed: September 18,
2010]
[2] http://gizmodo.com/317135/crealev-floating-lamp-leavens-any-room [Accessed:
September 18, 2010]
L3 (ECE4007L03-­‐04) 21 Appendix A: Gantt Chart
L3 (ECE4007L03-­‐04) 22 L3 (ECE4007L03-­‐04) 23