SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
1
The Design of a Wearable Non-Contact Voltage
Detector
Chris Crockett, Jason R. Gulley, Member, IEEE, Reuben Smith, Member, IEEE and Charles Smith

Abstract—This paper discusses the development of a non-contact
voltage detector, which is embedded into a multifunction glove.
The detector is able to detect 120V sources from approximately 1
foot away. The glove is intended to provide a worker who may be
exposed to hazardous voltages real-time feedback about the state
of the circuit and prevent inadvertent contact with such circuits.
It is not intended to be used as a primary testing device.
It was found that the optimal approach given the current state
of the art is a detector based on the principle of capacitive
coupling. Initial attempts at building a detector circuit with the
required sensitivity were fraught with false positives resulting
from sudden changes in capacitance induced by movement such
as walking. Ultimately, a simple algorithm was able to eliminate
the occurrence of false positives.
The development of the glove involved the testing of numerous
detector circuits and PCB layout and design which is described
herein.
incorporate non-contact voltage detection and thereby could
provide a worker with real-time feedback, these are rare and
present other problems such as necessitating the stocking of
batteries and introducing numerous points of failure. Still yet,
there are devices such as the V-WATCH which is wearable
and able to detect voltages at a distances of 6 feet or more, but
requires the source to be at least 4 kV in order to operate and
is intended for use by lineman [2].
Index Terms—capacitive coupling, non-contact, pen tester,
voltage detector, wearable.
I. INTRODUCTION
T
HE current state of voltage detector technology accessible
to workers, in fields where interaction with hazardous
voltages is required or routine, is for the most part limited to
devices which are intended to test a circuit before the worker
begins to operate on it. The state of the circuit while the
worker is operating is assumed to remain unchanged. This
lack of real-time feedback about the true state of the circuit
represents a potential hazard to people across numerous
industries and fields. Procedures intended to guard against the
re-energizing of circuits, such as lock-out-tag-out, are not
strictly followed and are one of the Occupational Safety and
Health Administration’s (OSHA) most cited violations [1].
Furthermore, homeowners, handymen and other do-ityourselfers often have no such training or protection
procedures in place and rely solely on those in their immediate
area being aware of their activity for their safety.
Devices intended to test circuits prior to operation are
primarily composed of dual and single probe test lights,
galvanometers, digital multi-meters (DMM) and pen style
non-contact testers. While there are several outliers such as
screwdrivers, wire strippers, pliers and other hand tools which
Figure 1-The V-WATCH Wearable Detector
Voltage detectors with two probes, such as the classic
“Wiggy” style tester, popular with electricians are incapable of
detecting voltage when the circuit is broken, i.e. when there
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
exists a ground or neutral branch wire which has become
detached from the system. For example, circuits being fed
from a sub-panel, where the ground and neutral are not
bonded, would not measure any significant voltage at an outlet
when tested with most two probe testers should the ground or
neutral fail at the panel. Pen style testers and single probe
testers remedy this problem by allowing a very small amount
of current to flow through the user completing the circuit.
Some multi-meters also incorporate the functionality of the
single contact testers and will light a warning light when a
hazardous voltage is present even if a high voltage across the
probes is not present during testing. Despite this capability,
these are still pre-test devices that do not provide real-time
feedback.
2
In light of this discussion it is apparent that there exists a
need for a voltage detection device that is 1) wearable, so that
it is always present while the person may be exposed to
hazardous voltages (for our purposes 120 V or higher), 2) able
to provide real-time feed back while a circuit is being operated
on and 3) has sufficient detection range to prevent contact
with an energized conductor. The focus of this paper is the
development and testing of such a device in glove form, which
is always on and capable of being worn for the duration of a
typical workday without needing to be recharged.
Patent applications for wearable voltage detector devices
similar to the one being discussed already exist, see Figure 3
below, but the availability of such products is non-existent [4,
5]. In addition, such devices have a narrow spectrum of
applications and are not versatile and save for operating on
their input and sounding an alarm, have no real processing
ability.
The design discussed in this paper uses a
microcontroller and thus has a robust capability for
incorporating sensors and processing inputs, to include the use
of sophisticated algorithms in order to adjust the detector
sensitivity. Furthermore, combining the functionality of a
non-contact pen style tester with microcontroller in wearable
form provides the opportunity to include numerous other
functions, which may prove useful to the wearer. Although
such a device could take nearly any form it was decided that a
glove would best meet our goal of optimizing safety. While a
creating such a device in a ring form had been originally
proposed it was decided that a glove would be ideal since, 1) it
would have the added benefit of preventing many injuries to
the hand, 2) workers already required to wear gloves may not
be able to wear a ring over or under them and 3) a glove
would not impose the additional burden of miniaturizing
existing technology and 4) a glove allows the opportunity of
multiple sensor inputs on each finger and greater battery
capacity.
Figure 2—An Electrician Testing a Circuit with a Wiggy
Beyond situations where a worker is purposefully working
on electrical circuits there exist many potential situations
where a completely unsuspecting person might inadvertently
encounter an energized surface; for example, in an industrial
environment one might lean against a control cabinet where
the ground has failed and it has become energized. A plumber
working on a residential system may be unaware that the
grounded conductor or neutral wire has become open and the
home’s current is being carried by the cold water system and
so on. In all, over 1000 people are electrocuted in the United
States each year [3].
Figure 3—Patent for a Wrist Wearable Voltage Detector
The team is composed of four seniors at Miami University
in Oxford, Ohio. Chris Crockett, Jason Gulley and Charles
Smith are electrical engineering majors whereas Reuben Smith
is a computer engineering major.
This report will discuss our research, design methods, some
conclusions and our future work.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
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II. DETECTOR RESEARCH
Our research was focused in two key areas, 1)
understanding how voltage detection at the ranges we were
interested in could be achieved and 2) implementing the
additional auxiliary functions that we felt would make the
device most useful, and therefore most likely to be worn. We
would need to learn many other things along the way
concerning microcontrollers and printed circuit board (PCB)
design however; these were learned as we went and not a
specific research focus.
A. Voltage Detection
We began our research into non-contact voltage detectors
by first attempting to determine the underlying principle of
operation. We first considered that the detector could be using
induction to detect the AC circuit. Inductive charging devices
are increasingly commonplace and we were sufficiently
familiar with this principle to feel that it could be employed
here. However, inductance requires a time changing current in
order to induce a voltage in the circuit to which it is coupled;
𝑑𝐵
according to Faraday’s Law of Induction: 𝑣 = 𝑛 .
𝑑𝑡
We knew that a strength of the non-contact detector was its
ability to detect hazardous voltages in wires which are not
connected and in which seemingly no current is flowing.
Without flowing current to create a changing magnetic field
we ruled this possibility out.
Next we considered the antenna principle. Here we thought
that perhaps the detector was simply acting as an antenna,
receiving the 60 Hz electromagnetic waves launched from the
AC lines and amplifying them to a useful level. We knew
from electromagnetics that to be an efficient antenna the
detector’s antenna would need be at least one quarter of the
wavelength long. Knowing that 𝑐 = 𝜆𝑓 taking f to be 60 Hz
and solving for lambda, our antenna would have to be 1250
km long. We knew this could not be the case, but thought
perhaps with sufficient amplification, this obstacle could be
overcome. We appealed this question to our advisor who felt
that it was highly unlikely and pointed us in the direction of
capacitive coupling.
We did some basic web based research into how the voltage
detector might function using this principle and submitted our
initial thoughts on how the detector circuit might function,
shown below.
The AC wire being tested couples with the tip of the
detector, forming the first capacitor of the circuit. The second
capacitor is formed through the surface area of the body going
to ground. Our advisor confirmed that this description is
fundamentally correct and based on this we continued to
investigate how this circuit could be used to detect voltage.
The key to understanding how this works lies in the
fundamentals of electric circuits. We know that the voltage in
a series circuit divides up proportionally among the
Figure
4 – Capacitive
coupling
sketch is 𝑧 = 1 so the
impedances.
Impedance
forconcept
a capacitor
𝑗𝑤𝑐
smaller the capacitor, the greater the impedance. In the circuit
above, the surface area of the detector tip and the wire being
tested form a much smaller capacitor than that of the surface
area of the body and the ground, so it’s impedance is much
higher. Accordingly the voltage across the detector tip should
be much higher than that across the body. By comparing these
values we can determine if there is a voltage source present.
We now consider an example with some notional values.
Let us assume the detector tip and the wire being tested
have a surface area of 1 cm2 and the distance between them is
10 cm. Let us also imagine that the body has a surface area of
two square meters and is separated from the ground by a
distance of 3 cm. In order to keep things simple we will
assume a dielectric of vacuum in both cases. Obviously a
truly analytical solution to such a problem would be
impossible and even closely approximating it through
simulation would not be an easy task but, this simple
calculation provides some insight into how the circuit
functions.
Calculating the capacitance of the first capacitor:
𝐶=
𝜀𝐴 8.854 × 10−12 (.01)
=
= 885.4 × 10−15 F
𝑑
. 10
For the second capacitor:
8.854 × 10−12 (2)
≅ 590 pF
. 03
Now we can calculate the impedances and use a voltage
divider to determine the results.
Impedance 1:
𝑧1 =
1
1
=
≅ 3 GΩ
𝑗𝑤𝐶 𝑗2𝜋(60) × 885 fF
Impedance 2:
𝑧2 =
1
1
=
≅ 4.5 MΩ
𝑗𝑤𝐶 𝑗2𝜋(60) × 590 pF
Now let’s assume 2 volts input and use voltage division to
see how it divides up.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛
𝑧1
3 GΩ
= (2)
≅ 1.997 V
𝑧1 + 𝑧2
3 GΩ + 4.5 MΩ
So we have confirmed that where the capacitance of the
detector tip is much smaller than that of the body and ground,
almost all of the voltage will be across the first capacitor.
With this in mind we focused our research on developing a
detector circuit.
Information from authoritative sources regarding the design
of such detector circuits was very difficult to find and we felt
that the principle of operation was sufficiently simple that we
could do most of the research ourselves in the laboratory.
Hence nearly all of our research is primary and represents our
own findings. After determining the principle of operation we
decided to teardown an existing non-contact detector to get a
gauge of the overall complexity of the device and to make sure
that it was something that we would be able to replicate. The
torn down detector is shown below.
4
It consists of three transistors with a β rating of 200
connected in such a way that the amplification that results is
β1 × β2 × β3 = 2003 = 8 × 106 gain. After building and
testing this circuit with transistors with a similar beta value,
we found its performance to be unreliable at best. The circuit
had several drawbacks, 1) it was unable to consistently detect
live circuits and 2) the range was very limited, a maximum of
a couple mm. We experimented with different resistor values,
input voltages, sensor strips and configurations, but we were
unable to get this circuit to function reliably.
We quickly realized that our transistor-based amplification
circuit was unrealizable due to its inability to faithfully detect
high voltages, of 120 V and higher, even at a very close range.
Additionally, we found that the circuit had far too many false
positives, which seemed to happen randomly. Even though,
occasionally, at distances of approximately three inches the
circuit would function as expected; we decided to scrap the
transistor approach altogether in lieu of something more
reliable.
C. Operational Amplifier circuit
Our second research focus was on developing an op amp
based detector. We had more experience using op amps than
transistors and hoped that they would provide a simple means
to create the needed circuit.
Initially we focused on the idea of using the venerable 741
op amp as a comparator as shown below.
Figure 5—Market-available detector
From this teardown we saw many recognizable components
and noted that the basic configuration of the device seemed to
be sensor → amplifier → output. Based on these findings and
the preceding discussion we decided to take two different
approaches to our research.
B. Transistor circuit
We found a very simple circuit for a transistor based
detector online at hackaday.com [1]. We will henceforth refer
to this as the hackaday circuit. The circuit was so simple that
we hoped that we would be able to modify it to meet our needs
and could then focus on other aspects of the project and
integration. The circuit is pictured below.
Figure 7 – Op-amp comparator design
Unfortunately this circuit had several flaws, which kept it
from working as desired. First, in this configuration the bodyground capacitor is not in series with detector tip and is thus
unable to exploit the voltage division principle, which we
discussed earlier. Second, using the 741 was a bad choice.
Due to inherent instabilities we always received an output
whether an input was present or not. We attempted to offset
this output by using the offset null pins on the op amp but
were unable to eliminate it to a satisfactory level. The third
factor, which impacted the operation of the circuit, was
Figure 6 – BC547 transistor-based design
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
attempting to use the 741 as a comparator; as it turns out the
sensitivity of the input pins makes this op amp unsuitable for
this type of application.
After looking back through our circuits book at different op
amp configurations we decided that an instrumentation
amplifier would be the best configuration for this type of
application since it would give us greater input sensitivity and
little dc offset. Using 3 741 op amps and the design shown
below we constructed another op amp based detector.
5
IC. Although initially flummoxed at how this could be
amplifying we found great information at [2]. It explained
how the inverter is able to amplify and provide some signal
generating abilities both of which are useful in the voltage
detector circuit. We then referenced a patent application
which we discovered while doing our background research
and found that it also used a hex inverter chip. The patent
circuit and our simulation are shown below.
Figure 9 – Patent circuit analysis
Figure 8 – Instrumentation amplifier
With V2 connected to our detector tip and V1 connected to
ground we were able to consistently light an LED within about
18 inches of 120 volt lines. We selected our resistor values to
provide a calculated gain of 100k. This circuit, though able to
consistently detect AC sources, also had occasional false
positives when large changes in capacitance occur. For
example, we found that we could light the LED for several
seconds by rocking our body over top of the detector circuit.
If someone were to walk near the circuit this change in
capacitance was picked up as well.
We replaced the trio of 741 op amps that comprised our op
amp detector circuit with a high precision instrumentation
amplifier from Texas Instruments the INA128P. This chip
provides very low drift current, 50 μV, and has the necessary
input sensitivity to make it suitable for medical devices such
as EEGs. While our group still encountered an unacceptable
rate of false positives in testing, they happened far less
frequently, and our new design proved much more reliable by
completely eliminating the false negative problems we
initially had. Movement seemed to be the key to our false
positive issues. Specifically, movement across the system’s
circuits or sharp, jerky operator movements seemed to cause
the issues. After allowing time for the sensor to settle after a
rapid movement, it seemed to operate consistently at distances
of one foot away from the voltage source. These large
movements appear to cause sudden changes in capacitance,
which activate the detector circuit.
D. Hex inverter
A closer look at the voltage detector teardown revealed that
what we thought was an amplifier was actually a hex inverter
Figure 10 – Patent circuit simulation
We now had a third direction mechanism on which to focus
our research. Provided that this type of IC was being used in
two known applications we were very optimistic that such a
design would provide the functionality that we were seeking.
Our simulation results confirmed that each stage of the circuit
matched our predictions. Furthermore, it represented an
elegant solution, which would allow us to simplify our design.
The IC used in the voltage detector that we tore down was
produced by Texas Instruments, a 4069UB. Though it is no
longer in production. We obtained several suitable
replacement chips and used them to realize the design
described in the patent circuit for a non-contact voltage
detector. This implementation behaved extremely similar to
the aforementioned instrumentation amplifier based detector,
occasional false positives primarily due to large, sudden
movements. With this design body movement over the circuit
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
didn't cause any unacceptable behavior. We believe that the
alarms induced by body movement for these designs are the
result of the high sensitivity needed to detect voltages at these
distances.
E. Microcontroller
Ultimately, we realized that each of these circuits regardless
of their effectiveness was striving to do the same thing: detect
voltage across the body by inserting themselves in series with
the body as shown in Figure 4. We then recognized that they
were all superfluous since we were already committed to using
a microcontroller for other functions. Our detector circuit is
then based on using the analog read capability of the
microcontroller. A simulation, Figure 11, of a 120V AC
source coupled to the body using similar capacitance values to
the earlier problem shows that a voltage of several volts, green
trace, exists at the point just before the resistor, which is that
impedance of the human body. To detect voltage we only need
to insert our voltage probe in series with the body at this point.
This large of a signal is easily readable using the ADC found
on a microcontroller. Approximately 118V drops across the
first capacitor, which again is the air gap between the source
and the body. This is an instance of the simplest solution
being the best solution.
Figure 11 – AC coupling Simulation
III. AUXILIARY FUNCTIONS
Safety was the driving force behind our research and design
decisions for this project. We knew that no matter how great
our glove might function in detecting voltage, if it was a
hardship to wear people wouldn’t use it. To that end we
strived to make it as useful as possible by incorporating as
many practical functions as we reasonably could.
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A. Stud Sensor
We felt that a stud sensor would be one of the most useful
items to a maintenance worker or construction worker and
since they used capacitance to operate we felt that this was
worthwhile pursuit.
We began by doing basic web research into the operation of
stud sensors and found that there were two primary types,
magnetic and capacitive. The magnetic type generally works
by making a noise when a magnet inside a housing is pulled
towards the metal nails in wood studs. We felt this was
impractical to implement into our glove.
The capacitive type work by using the change in
capacitance created when the dielectric material changes. We
referenced the original patent [3] for the first stud finder and
noticed a component that we were unfamiliar with a one-shot
multivibrator. We surmised though that circuit was essentially
working by using two capacitors set up in such a way that
when both were charging at the same rate the oscillations in
the circuit would cancel out. However if one capacitor was
placed over a wooden stud, they would charge at different
rates and an indicator would alert the user to the presence of
the stud.
We decided that we could do this by using the
microcontroller to charge and discharge a capacitor repeatedly
and then compare the charge times. We felt that a wood or
metal stud would increase the capacitance and the charge time.
This approach was not successful because the charge times
varied wildly whenever we attempted to move the plate of our
capacitor along the wall, whether a stud was present or not.
Next we decided that perhaps it would be easier to detect
only metal studs. We developed a design, which used
neodymium magnets and a Hall effect sensor to detect the
studs by sensing when the magnet was able to sink flux into
them. The design is shown in Figure 12.
Figure 12 – Stud Finder Design
Our initial tests with this were very successful. We found
that we could detect stud edges on par with an inexpensive
commercially available detector. However in handling the
glove we broke the Hall effect sensor. When we tried to
rebuild the stud finder with a new Hall effect IC we had little
success and couldn’t even detect ferrous metal surfaces from
only millimeters away with no obstructions. This behavior is
obviously not correct; the sensor should be able to sense a
change in the magnetic field strength at these distances. We
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
believe there were two problems affecting stud finder, 1) the
placement of the IC in relation to the magnet is critical, it
cannot be so close that sensor is saturated because it has a
significant recovery time and 2) the natural bending of the
hand in the second iteration, created a constantly changing
relationship between the IC and the magnet causing unreliable
measurements.
With our time dwindling we felt that we could not afford to
devote any more resources to the stud finder and needed to
focus on other aspects of the project. We do feel however,
that our design is fundamentally sound and capable of
faithfully detecting metal studs.
B. Flashlight
A flashlight is a staple of most toolboxes and is extremely
useful. The challenge for incorporating it into the glove
revolved around power draw and component selection. Most
small AA powered LED flashlights have a light output around
100 lumens and most small key chain or cell phone lights
provide 30-45 lumens. We initially, wanted to provide 200
lumens so that the flashlight would be powerful enough to be
considered an excellent flashlight in its own right. However
the current draw would have been 750 mA, far more than our
power supply, a lithium CR2032 coin cell battery could
produce. Even at 100 lumens we couldn’t meet the power
requirement without changing our power supply to AA
batteries, which we felt, would make the glove bulky and
unwieldy. So we compromised and decided to provide a 30
lumen light source which would provide the user a useful
amount of light to find things in a dark room but, not
necessarily enough to work by. We were able to limit the
current draw to only 10 mA.
C. Laser Pointer
The need to highlight features, which are high off the
ground or not accessible, is common in construction and
maintenance environments so the decision was made to
include a laser pointer so the wearer could easily point out
things of interest to coworkers. A green laser diode was
desired so that it would be highly visible during the daytime
however this was cost prohibitive. A red laser diode, which is
eye safe and draws only 40 mA was used instead.
IV. DESIGN
We began by deciding which CAD software to use for
developing our schematic and board. We chose to use free
software from a PCB production house called Express PCB.
This software has a very small learning curve and enabled us
to get started quickly. However it’s component library was
very limited and we had to make most or our parts which was
time consuming. Also this software locked us in to using
Express PCB for our production. Our original schematic and
PCB layout is shown in Figure 13. Although we had laid out
the board, we still needed to add the traces and we felt that this
software was too simplistic and not professional enough to
meet our needs.
So we started over using Eagle, which is developed by
OrCAD, the makers of PSPICE. This software was also free
in a limited form, but offered a steeper learning curve. It was
much easier to use though once we got used to it. It also had
7
the advantage of allowing us to export our Gerber files so that
we were free to choose a production house.
Figure 13 – Original Schematic and PCB Design
A. Microcontroller
To realize our design we chose to build around the
ATMega328p microcontroller, which is sold by Atmel. We
had experience using this processor with Arduino on which,
we built our prototype designs, see Figure 14. Most
importantly we selected this microcontroller so that we could
use the Arduino to program it and use our prototype code
without having to make any modifications. As it turned out
though, we were unable to use the Arduino Uno to program
the chip and were forced to buy a programmer from Atmel.
This microcontroller has a built in 8 MHz clock, however, we
chose to use an external oscillator, which increased the clock
speed to 16 MHz. We felt that this allowed us the greatest
freedom in that if the battery drain was too significant at 16
MHz, we could simply cut the traces and use the internal
clock.
B. Power Supply
When selecting a power supply we wanted something with
a low profile so that it would be as unobtrusive as possible so
we selected 3V lithium coin cell batteries, specifically the
CR2032. This battery is commonly found in watches and
would not be hard for the user to replace. Our testing showed
that a single cell could sustain 70 mA for at least 5 minutes.
Our max load is 40 mA which is drawn by the laser diode, so
we decided to parallel two batteries to increase life. We
placed a 47 𝜇𝐹 capacitor in parallel for stabilization.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
Figure 14 – Prototype Glove and Microcontroller Design
The batteries connect to a 3.3 volt regulator specifically
designed for microcontroller applications. It has a drop out
voltage of 200 mV for an output load of 100 mA. This allows
us to extract the maximum life from our batteries. The
CR2032 maintains its voltage well under load. Assuming the
processor is not sourcing power from any of its pins it draws
around 30 mA. The voltage regulator has a quiescent current
draw of 400 𝜇𝐴. So the total standby load of the glove is
around 30.5 mA. According to data from the manufacturer a
CR2032 has approximately 240 mAh of energy before the
voltage drops to two volts. See Figure 15 below.
8
C. Hand Detection
In order to function, the detector circuit must have a solid
electrical connection to the hand. In many voltage detectors
this is accomplished by using a conductive switch, which the
user presses to operate the device. We chose to accomplish
this by installing a small disc shaped electrode near the base of
the glove. A good connection is established by latching the
gloves Velcro fastener. However a potentially dangerous
situation exists where the user may be unaware that the
grounding connection has failed and the alarm will not sound.
To address this scenario we equipped the glove with a hand
detection circuit. This circuit has two functions; alert the user
to a bad connection and to sense the hand, waking the
processor from a low power sleep state.
We implemented this by using three equidistant electrodes,
which run along the back of the wrist as shown in Figure 16.
Figure 16 – Hand Detection Circuit
Figure 15 – Battery Performance
With this being the case we can expect beyond 16 hours of
standby life from our batteries, which is double the target we
set for the glove of being able to protect a worker throughout a
typical workday.
In a finished product using a molded battery, which would
occupy the area on the bottom of the PCB, would increase this
battery life. It would also be rechargeable. We included a
battery jack in the original design for this purpose. However,
we decided that using disposable batteries was acceptable at
this point.
Using the device’s functions will of course significantly
reduce Battery life; for example the laser can only be powered
for 8 hours.
The three electrodes form a voltage divider with the
resistance of the wearer’s skin. If the ground electrode loses
contact then the analog pin will register logic high of 3.3V. If
the Vcc connection is lost the analog will be pulled to ground.
If both Vcc and ground are lost then the analog voltage will
float around the noise floor, which is also distinct. So in this
manner we are able to alert the user to any malfunction, which
would leave them unprotected. In the normal state the analog
pin will be approximately half of Vcc.
A small metal tab, which connects to an IO pin and to Vcc
when the hand is inserted, is used as a switch to wake the
processor.
D. Gesture Control
In order to prevent the user from having to use both hands
to activate the glove’s functions we gave the glove gesture
recognition functionality. We used flex sensors, which are
actually variable resistors, which track with the middle and
index fingers of the hand to form voltage dividers. Monitoring
the voltage using the analog input allows us to know the
position of both fingers. Ideally, this set-up would offer very
high resolution however, the flex sensors do not at all live up
to the datasheet and are very inconsistent so the detection is
quite coarse and we only distinguish a 90° bend of the finger.
To activate the flashlight the user closes their fist. In order
to turn on the laser the user points with their index finger. To
activate the stud sensor when it was part of the design, the user
kept the palm and fingers straight for several seconds like
making a stop sign. Using this scheme the user can control
multiple functions while continuing to work with their other
hand.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
E. Indication
In order to alert the user to hazardous voltage both visual
and aural indicators were used. Green and red LED arrays
provide alarm and status indication in conjunction with a piezo
electric speaker.
F. Detector
The detector is composed of a thin magnet wire, which has
been distributed throughout the glove to maximize its area and
provide the wearer with the most protection. The wire acts as
the tip of the electrode in a typical connector. It is connected
to the ADC of the microcontroller along with a 50 M Ohm
pull down resistor to eliminate noise. A Zener diode is used to
protect the microcontroller from any high voltages, which may
damage it.
G. Code
Insert stuff about the code here. How the detector algorithm
works. The general approach. Maybe a screen shot. Perhaps
talk about the ide used. Doesn’t have to be long.
H. Circuit Board
Our circuit board design can be seen in Figure 17 below.
Figure 17 – Circuit Board Design
Once we had completed our schematic we used Eagle’s
ability to link the schematic to a PCB design. This allowed us
to autoroute the traces, which saved us much time. The
express PCB software would only highlight the components,
which were to be connected. We made custom parts as
needed by referencing the device’s datasheet.
V. COSTS
Much of the component cost of our design is due to a few
key items; namely the flex sensors and the laser diode. These
are obviously nonessential and could be eliminated to make
the glove more competitive with traditional non-contact
voltage detectors which retail from $7-$50. It is also worth
pointing out that the work glove itself is a significant cost and
that this should be considered when making judgments about
the financial potential of the product. The glove must be very
long lasting in order to justify the expense of the electronics.
It would be possible to develop the glove in two parts, a tough
but inexpensive disposable outer shell which the user could
cheaply replace and an insert which houses the electronics.
This in fact, how our prototype is constructed. By doing this
9
the glove has the potential to last many years and allow the
user to feel justified in their purchase. The complete bill of
materials is presented in Table 1.
TABLE 1 – BILL OF MATERIALS
Item
QTY
Part Number
Flex Sensor
2
FS-L-0095-103-ST
Laser Diode
1
VLM-650-03-LPA
Coin Cell
Battery
Microcontroller
Piezo
Buzzer
Glove
1
CR2032-VP
1
Atmega328-AUR
1
CMT-1075-SMT
1
CLC WorkRight XC
Electrodes
3
Wire
Voltage
Regulator
Battery
Holder
10k Resistor
1
LT1528
1
BU2032SM-BT-GTR
4
ERJ-8ENF-1002V
301 Resistor
3
RNCP1206-FTD301R
22k Resistor
1
ERJ-8ENF-2202V
30k Resistor
1
ERJ-8ENF-3002V
50M
Resistor
Red LED
1
HMC1206JT50M0
2
APTD32166SRCPRV
Green LED
2
APTD3216CGCK
Flashlight
LED
22 pF
capacitor
100 nF
capacitor
47 uF
capacitor
Zener Diode
1
2
MTG7-001I-XQB00-CWL053
CL31C220JBCMNNC
1
T491A104M035AT
1
TLNK476M010R1500
2
1N472748A
16 MHz
Crystal
1n148 Diode
1
ECS-160-20-3X-TR
1
1n148 Diode
ICSP
Header
Total
1
PRT-10877
36
Unit
Cost
Cost @
5000
$15.88
$8.26
$13.18
$6.87
$0.40
$0.20
$2.88
$1.78
$4.12
$1.81
$12.00
$12.00
$0.15
$0.15
$0.50
$0.50
$7.13
$3.70
$0.60
$0.35
$0.10
$0.01
$0.09
$0.01
$0.10
$0.01
$0.10
$0.01
$0.73
$0.10
$0.28
$0.08
$0.35
$0.10
$6.00
$2.48
$0.16
$0.03
$0.38
$0.11
$2.40
$0.91
$0.25
$0.04
$0.53
$0.21
$0.12
$0.02
$1.50
$1.20
$87.63
$49.26
The cost presented here does not include consumables such
as solder paste or the cost of board production and assembly.
The cost for two boards was $60 and $30 was spent on an in
system programmer. Another $30 was spent on a laser cut
solder paste stencil. For a production run however, the board
cost would be very low perhaps $1 per board. Our board was
designed with assembly in mind; using almost all surface
mount components so most of the work could be done by a
pick-and-place machine. Our total project development cost
included buying extra materials and items that were never
used and is approximately $270. From the table we can see
that with economies of scale the glove could be reasonably
priced versus buying a work glove, laser pointer, flashlight
and non-contact voltage detector separately. Removing the
flex sensors and laser diode would cut the costs almost in half
making the glove an excellent value and competitively priced.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
VI. CONCLUSIONS AND FUTURE WORK
The performance criteria set forth for voltage detection
range; battery life and auxiliary functionality were all met or
exceeded. The strength of the design is how well it is able to
detect voltage at considerable distances. A weak point in the
design is the flex sensors, which are not rugged enough for a
production version and are excessively expensive for the value
they bring. Another potential liability is requiring the
electrodes to contact the skin in order to function.
This was a major challenge for us because we all had no
real design experience coming into the project. So it was not
so much a confirmation of prior learning, but a novel learning
experience in and of itself. To that end we decided to include
as much rigor and get as much out of the project as we
possibly could. So wherever we had a chance to take an easy
route we chose a harder one. We could have used a small
prototyping board to realize our design, but we would have
lost the opportunity to learn about PCB design. We could
have used hobbyist design tools, but we would have lost the
opportunity to learn how to use professional software.
In future refinements we would like to add a decreased
sensitivity mode that could be entered by pointing the index
finger so that the glove would behave as a typical non-contact
detector, allowing the user to identify specific conductors
within an enclosed space. This could be achieved solely
through software and would only add to the usefulness of the
glove.
We would also like to incorporate a battery indicator to alert
the wearer of its status. We feel this could be easily added by
reading the battery voltage before the regulator using the
microcontroller’s ADC.
VII. THE TEAM
A. Chris Crockett
Chris Crockett is in his fourth year at Miami Ohio who is
majoring in electrical engineering. His skill set that is relevant
for this project consists of organizing, circuit analysis and a
good understanding of electronics. His learning background
consists of minor home electrical wiring, lecture courses at
Miami Ohio, lab courses at Miami Ohio and various helpful
internet websites. He is inexperienced in the professional
world.
Chris' major contribution toward this project was
determining if the transistor based non-contact voltage circuit,
with Ryan Smith, that the team found on www.hackaday.com
would be sufficient design for this project. They rebuilt the
circuit from this site and started to test it. They came to a
conclusion that this original design was too inconsistent. They
did multiple adjustments toward this circuit in order to try to
get it to work more consistently such as adding more
transistors, attaching copper then aluminum plate at the end of
the sensor and adjusting the voltage value. All of these
methods failed in producing a more consistent non-contact
voltage detector.
B. Jason Gulley
Jason is a highly motivated and detail oriented team
member. He is a non-traditional student with an eclectic work
10
history, which includes selling cars, retail management,
working as an electrician and serving two tours in Iraq as an
Infantry Assaultman in the Marine Corps.
Jason’s learning style emphasizes repetition to reinforce
new skills and prioritizes obtaining conceptual understanding
over mechanical manipulations. He is skilled in the areas of
basic programming, power electronics, control systems,
electric drives and circuit simulation software.
In terms of professional experience, Jason worked as an
electrician in both the residential and commercial segments for
several years. He participated in the Associated Builders and
Contractors Apprenticeship Program and received his
Journeyman Electrician License from the State of Kentucky in
2002. He studied permanent magnet generators and aircraft
electrical generation systems while working for GE Aviation
Systems in 2012 and has worked on testing for a new product
development concerned with the control of high inertia
engines. He has been accepted to the Edison Engineering
Development Program at GE where he will work with aviation
systems while pursuing a Master’s of Science at Michigan
State University.
His contributions to the project include, conceiving of and
proposing the initial project idea, conducting extensive
background research, assisting in the design, testing and
simulation of the detector circuit, design of the stud finder,
hand detection and gesture recognition functions,
spearheading the development of the design schedule,
developing the presentation slides and acting as a liaison
between the faculty advisor and the group. Jason is a member
of the IEEE-HKN honor society for electrical and computer
engineering students.
C. Charles Smith
Charles "Ryan" Smith is a senior at Miami University
Oxford. He is attending Miami to earn a bachelor's degree in
Electrical Engineering. When he originally enrolled at Miami
he was actually a nursing major which eventually lead to
electrical and computer engineering technology at the regional
campus, which finally put him where he is at now. At the
current state he doesn’t have much experience in the work
field related to electrical engineering, but hopes to gain
experience going into his final semester before graduation. He
hopes that gaining the work experience will guide him towards
a primary focus in the electrical field.
Charles has a wide variety of skills that have been properly
implemented during the process of this project. Some of the
said skills are Circuit analysis, variety of programming
language knowledge, and control systems. Charles’ learning
style is more of the hands on approach. Accomplishing tasks
and completing problems properly is his key method of
learning.
Major contributions thus far primarily deal with working on
the original transistor based approach along with Chris
Crockett. This circuit was modeled after a design we found on
the website Hackaday.com and was recreated with slightly
different components, primarily transistors.
SENIOR DESIGN 448 - WEARABLE NON-CONTACT VOLTAGE DETECTOR
D. Reuben Smith
Reuben Smith is a Miami University senior undergraduate
majoring in computer engineering and minoring in computer
science. Leveraging these studies, his research focus for the
project has been on microcontroller integration and user
experience design. Past projects at Miami include an
implementation of Atari's PONG on the Altera DE2, a multithreaded negamax AI player for the board game Breakthrough,
an Undergraduate Summer Scholars research grant to study
the use of games in teaching students Verilog, and a
submission to Miami's Global Game Jam event.
Outside of university-related studies and projects, Reuben
enjoys game development, especially development with a
strong use of procedural content and an emergent experience,
linguistics and constructed languages, things that fly, and
applied ballistics engineering. He is certified CompTIA A+
and is certified to use Motoman's NX100 industrial robotics
controller. He is also a student member of ACM and IEEE. In
the future, he hopes to work for a company that uses
computers to make the world a better and more enjoyable
place.
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ACKNOWLEDGMENT
We would like to thank our advisor Dr. Garmatyuk for his
help in selecting this project, starting us on the right path and
his guidance along the way.
REFERENCES
[1] Occupational Safety & Health Administration. (2012).
Commonly Used Statistics. [Online]. Available:
http://www.osha.gov/oshstats/commonstats.html.
[2] W. McNulty, “Voltage Detection and Indication by
Electric Field Measurement,” in 2011 IEEE PES 12th
International Conference, Providence, RI, 2011.
[3] Franklin, Robert, C. “Electronic Wall Stud Sensor,”
U.S. Patent 4,099,118, Jul. 4, 1978.
[4] The Law Offices of David H. Greenberg. (2012).
Electrocution: An In Depth Look at Injuries. [Online].
Available:
http://www.greenbergaccidentlawyer.com/electrocution
-an-in-depth-look-at-injuries.html
[5] Ojeda et al., “Wearable live electrical circuit detection
device,” U.S. Patent 2011/0234414 A1, Sep 29, 2011.
[6] Jones, Richard, K., “Wrist wearable electrical detection
device,” U.S. Patent 2008/0024265 A1, Jan. 31, 2008.