the design of a wearable non contact voltage …...detecting voltage when the circuit is broken,...

SENIOR DESIGN 449 - WEARABLE NON-CONTACT VOLTAGE DETECTOR

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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. Index Terms—capacitive coupling, non-contact, pen tester, voltage detector, wearable.

I. INTRODUCTION 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-it-yourselfers 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 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].

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 exists a ground or neutral branch wire which has become

The Design of a Wearable Non-Contact Voltage Detector

Chris Crockett, Jason R. Gulley, Member, IEEE, Reuben Smith, Member, IEEE and Charles Smith

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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.

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]. 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 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.


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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; according to Faraday’s Law of Induction: 𝑣 = 𝑛 !"

!".

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 to 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 impedances. Impedance for a capacitor is 𝑧 = !

!"# so the

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 =𝜀𝐴𝑑=8.854×10!!"(.01)

. 10= 885.4×10!!" F

For the second capacitor:

8.854×10!!" 2. 03

≅ 590 pF

Now we can calculate the impedances and use a voltage divider to determine the results.

Impedance 1:

𝑧! =1𝑗𝑤𝐶

=1

𝑗2𝜋 60 ×885 fF≅ 3 GΩ

Impedance 2:

𝑧! =1𝑗𝑤𝐶

=1

𝑗2𝜋 60 ×590 pF≅ 4.5 MΩ

Now let’s assume 2 volts input and use voltage division to

see how it divides up.

Figure 4 – Capacitive Coupling Concept Sketch


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𝑉!"# = 𝑉!"𝑧!

𝑧! + 𝑧!= 2

3 GΩ3 GΩ + 4.5 MΩ

≅ 1.997 V

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.

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.

It consists of three transistors with a β rating of 200

connected in such a way that the amplification that results is β!×β!×β! = 200! = 8×10! 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.

Unfortunately this circuit had several flaws, which kept it

from working as desired. First, in this configuration the body-ground 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

Design Process

LED

Potentiometer

Detector Tip Switch

Piezo Speaker

Battery Conn.

Amplifier

Figure 7 – Op-amp Comparator Design

Figure 5—Market-Available Detector

Figure 6 – BC547 Transistor-Based Design


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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.

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

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 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

A Striking Similarity…

Amplifier Gating Oscillators

Simulation Results

4 3 2 1

1

4

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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.

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


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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

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.


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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.

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.

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

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.

Figure 17 – The Electrodes Of The Hand Detection Circuit

A small metal tab connects to an IO pin and to GND when

the hand is inserted; it is 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


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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.

Figure 18 – The Flex Sensors During Testing

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. Circuit Board Our circuit board design can be seen in Figure 19 below.

Figure 19 – 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.

Figure 20 – Circuit Board Before the Reflow Oven

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 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.


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TABLE 1 – BILL OF MATERIALS Item QTY Part Number Unit

Cost Cost @

5000 Flex Sensor 2 FS-L-0095-103-ST $15.88 $8.26 Laser Diode 1 VLM-650-03-LPA $13.18 $6.87 Coin Cell Battery

1 CR2032-VP $0.40 $0.20

Micro-controller

1 Atmega328-AUR $2.88 $1.78

Piezo Buzzer

1 CMT-1075-SMT $4.12 $1.81

Glove 1 CLC WorkRight XC $12.00 $12.00 Electrodes 3 $0.15 $0.15 Wire $0.50 $0.50 Voltage Regulator

1 LT1528 $7.13 $3.70

Battery Holder

1 BU2032SM-BT-GTR $0.60 $0.35

10k Resistor 4 ERJ-8ENF-1002V $0.10 $0.01 301 Resistor 3 RNCP1206-FTD301R $0.09 $0.01 22k Resistor 1 ERJ-8ENF-2202V $0.10 $0.01 30k Resistor 1 ERJ-8ENF-3002V $0.10 $0.01 50M Resistor

1 HMC1206JT50M0 $0.73 $0.10

Red LED 2 APTD32166SRCPRV $0.28 $0.08 Green LED 2 APTD3216CGCK $0.35 $0.10 Flashlight LED

1 MTG7-001I-XQB00-CW-L053 $6.00 $2.48

22 pF capacitor

2 CL31C220JBCMNNC $0.16 $0.03

100 nF capacitor

1 T491A104M035AT $0.38 $0.11

47 uF capacitor

1 TLNK476M010R1500 $2.40 $0.91

Zener Diode 2 1N472748A $0.25 $0.04 16 MHz Crystal

1 ECS-160-20-3X-TR $0.53 $0.21

1n148 Diode 1 1n148 Diode $0.12 $0.02 ICSP Header

1 PRT-10877 $1.50 $1.20

Total 36 $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.

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


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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.

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 multi-threaded 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.

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.

the design of a wearable non contact voltage …...detecting voltage when the circuit is broken,...

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