Multidisciplinary Senior Design ConferenceKate Gleason College of Engineering

Rochester Institute of TechnologyRochester, New York 14623

Project Number: P12036

NTID NOTIFICATION ALERT PHASE II

Michael MyersMechanical Engineering

Matthew GesnerElectrical Engineering

Joseph GaglioneComputer Engineering

Cory DuellElectrical Engineering

Alvaro BercerueloElectrical Engineering

Scott TuckerElectrical Engineering

ABSTRACT

The primary objective of this project is to develop a portable, programmable alarm system for the deaf and hard of hearing. The alarm system is a small, pocket-sized device designed to awaken deaf/hard of hearing users with high intensity lights and a bed shaking device. The high-level function of this device is to - as previously mentioned - awaken deaf users in a similar manner to an alarm clock, with a programmed alarm activating the lights and the shaking device. The low-end functionality includes a rechargeable battery, luminous state indication, a small microprocessor, and a Bluetooth transceiver. The alarm activation time is programmed via a PC, with the eventual goal of the alarm’s device being set with the use of a smartphone, particularly making use of its Bluetooth capabilities.

NOMENCLATURE

Bed Shaker – Device with counterweighted motor used to vibrate the bedLED – Light emitting diodeMSP430 / MSP430BT5190 – Microcontroller usedPAN1325 / PAN – Bluetooth module with antennaPCB – Printed circuit board

BACKGROUND

This project started when the customer identified a need in the deaf or hard of hearing community for a small and inexpensive module to serve as a mobile alarm clock or emergency alert notification. To satisfy this need this team designed, built, and tested a small, portable accessory with the ability to control a bed shaker and high intensity lights via an application from a cell phone or similar Bluetooth enabled device. A secondary objective of this project was to design the Bluetooth transceiver and micro-controller to be modular in design such that they could be used in a variety of different applications.

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This project is the second phase and has many improvements over the first phase, after exploration of several enhancements. Higher intensity LED's surface mounted to the exterior of the device would allow for a greater luminosity at a wider viewing angle, were a first-priority requisite. Another such improvement was an internal lithium-polymer battery that would improve the mobility of the device and allow it to be used separate from a wall socket. A functioning prototype that aimed to be smaller, lighter, and cheaper than the previous proof of concept design was another of the main objectives to be accomplished in this second phase of the project. A CAD package, circuit layout, and an instruction manual will also be delivered at project completion. The scope of this phase can be summarized in the following bullet points:

Reduce the cost to manufacture a given number of devices. Reduce size of the device allowing for easier transportation. Improve performance by expanding the number of Bluetooth devices capable of communicating with the

physical device. Improve appearance and overall aesthetics.

PROCESS

The team first identified the project requirements by acquiring customer input through surveys. The critical customer specifications are shown below.

Device must use Bluetooth to communicate with PDA/smartphone Device must activate even if PDA/smartphone becomes inoperable Device must be compact Device must activate high-intensity lights and a bed shaker Device must be powered off a rechargeable battery Device must be kept inexpensive Device must indicate when power is on, when alarm is set, and when device is communicating with the

PDA/smartphone Device must have both an “OFF” switch and “snooze” functionality

The team first started with the idea the device was going to have to be small; we designed all our systems with PCB usage and component size in mind. The device needs to be Bluetooth capable in order to communicate with a PDA or smartphone and therefore FCC compliant. Moving forward, these were our biggest foci. From the design specs, one member derived several different concept sketches of what this project may look like.

Figure 1: First Concept Drawing of Device Figure 2: Second Concept Drawing

Bluetooth moduleThe device needed wireless communication but FCC compliance bottlenecked the options for the Bluetooth

controller and the microcontroller, as there was really only one cost-effective combination (the MSP430BT5190 + PAN1325) that fit specs for both cost and size. The PAN1315 was also available, however it did not come with its own antenna, and the tuning network would need to have been designed and optimized. The control circuitry was designed based on the datasheets given.

Alert System

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The alert itself featured the ability to activate a bed shaker and lights. Given that the lights had to be bright enough to be seen even when eyes are closed, we investigated high-intensity LEDs. The chosen LEDs were picked for their moderate current and a demonstration from one team member from ones he already had. Simple control circuitry involving a high-power BJT was designed around the spec that the lights need to blink, and not just be on. The BJT and resistor values for the LEDs were picked based on power requirements.

The bed shaker itself was not in our original needs, so therefore we purchased a premade bed shaker. A control box was designed to interrupt the bed shaker’s outlet power with a power BJT, whose signal is connected to the primary device via barrel jack. The shaker would then be software controlled.

BatteryFrom the customer needs, the device was required to be battery operated and rechargeable. We looked

specifically into cell phone–type batteries mainly because they have already been proven to be able to display bright lights, have high power specs, and last for long lengths of time. We settled on this battery based on the ability to charge it through USB, the battery regulator available, and the output current capabilities. A power analysis was completed as shown below to estimate the battery life of the device under normal usage assumptions.

Power RegulationThe battery itself already had a recommended voltage regulator specifically built around charging this battery.

However, the voltage needed for the high intensity LED was higher than originally thought, and therefore needed a boost converter to increase the voltage to 5V. Under the assumption that power is conserved and that we already estimated our power consumption (shown below) we selected an adequate boost converter and external circuitry.

The MSP and the PAN1325 both needed their own supply, however it is below the battery voltage and low power, so there are two regulators to limit the voltage supplied to them.

IndicationThis device needed feedback to let the user know when the device is on, when the device is charging, when the

device is connected via Bluetooth, and when the alarm is set. The simplest implementation is to have 4 indicator LEDs; One red for device charging, one red for device “ON”, one blue with additional software-controlled BJT for Bluetooth connected, and one software-controlled green for alarm set.

SchematicGiven that we had already chosen the major components (MSP/PAN1325, the indication, and power

regulation), the overall circuit was designed. Most component design and selection were derived from the datasheets of each individual device, with appropriate stock components selected. The entire schematic was minimalist in that if there was extra functionality in a portion of the circuit (shutdown signal to the boost converter, for example), it was largely omitted in favor of simplicity, size, and customer needs.

PCB LayoutThe printed circuit board consists of top layer, bottom layer, and a silkscreen. This allowed for smaller

components and circuitry to be placed on the underside of the board thus saving precious space. The USB power jack and the barrel jack were kept to one side of the board with final product aesthetics in mind. Most regulation circuitry is kept isolated from everything else in case the board was not printed correctly or a redesign was needed. The MSP and the PAN1325 were kept to the far right of the board for purposes of keeping the antenna away from as much electronics as possible, to reduce noise and crosstalk. A secondary reason for keeping the Bluetooth to that side is that the customer wanted to be able to break that section of the board off, and use it for future applications. For this purpose, we included a Molex connector with connections to generic input/output pins on the microcontroller. Extra holes were included for mounting screws. The alert LEDs were on a separate board, connected via Molex.

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Figure 2: Final PCB Layout

HousingThe biggest concerns in design of the housing of the device were size constraints, manufacturability, structural

integrity, and aesthetics. The final design resembles one of the concept drawings in appearance. The first major design considerations were the location of the LEDs, which direction they would be facing, and what the viewing angle was. Because the LEDs need to rest as close as possible to the outside of the case for best possible light, the alert LEDs were included on a PCB separate from the main one. Based on the dimensions of the battery and the PCB, the other internals were included in the design and assembly plan. Although the device could have been smaller, it would have been much harder to assemble. To avoid difficulty assembling, the indication LEDs stand off from the PCB and rest in the holes in the top of the case. Because the battery size was inconvenient, the mounting of the PCB is done on struts that are mounted above the battery. The ON/OFF switch is mounted as to be flush with the outside of the case to prevent accidental switching.

After minimum dimensions and placement was finished an analysis on stress and temperature was completed with the design. Using the process shown below a minimum thickness was calculated to give the device reasonable strength. The temperature analysis was based off power assumptions for each individual device.

Figure 3: CAD Renderings of Complete Device with and without the Lid

Snooze Functionality

Since all the alarm is set and controlled with the use of a software application the need for a snooze physical snooze button was thoroughly discussed. A button that could be aesthetically pleasing to the user would be very difficult to implement due to the dome shape of the device. Therefore, a tilt switch that would play the role the button was elected to be the best solution to the problem. In order to “hit” the snooze button the user would have to shake the device. This shaking motion will be captured by the tilt switch and processed by the microcontroller. The tilt switch itself is a three-pin device with the center pin connecting to either outer pin when it is tipped more than 45 degrees in that direction. The software recognizes this as “snooze”.

Software

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The Bluetooth solutions for the MSP430 were limited, two options were explored; TI’s pre-integrated system solution CC2650 and a third party Bluetooth solution, BTStack. Development was explored using both solutions and TI’s CC2560 Bluetooth Platform was the first to show results and was then chosen for continued development. MSP430BT5190+CC2560 has a supplied Software Development Kit (SDK) which includes MindTree’s Bluetooth Ethermind Stack with Serial Port Profile (SPP) as well as code for sample projects. Using the Simple SPP sample project as a base the wake up system functionality was developed.

For the PC, 32feet.NET shared-source project was used in the end-user application development. The project supports PC, mobile devices and embedded systems and includes a SDB browser tool for testing Bluetooth services used in development. The end user application was developed in Visual Basic to streamline the creation of the user interface and to allow more development time on the Bluetooth end of the application.

Figure 4: Software Behavioral Flowchart

Stress Analysis: Since the case is to be build out of ABS Plastic, a stress analysis was performed to ensure that the enclosure

would be durable to handle travel and everyday use. A load of roughly 100 lbs with a factor of safety of 1.5 were used in a stress calculation as a basis to find the required material thickness for the enclosure. The maximum flexural stress of the ABS material is 53 MPa, so this was used in conjunction with the safety factor for a conservative thickness calculation. As shown below, the calculation yielded a base thickness of 3/32” for the case, and this was used for the Finite Element Analysis in Solidworks to confirm a structurally sound design.

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Uniform Load:

=

334 KPa

Thickness Equation: β = 0.1794 from Roark’s Table 14.4

m = 0.091”

Therefore the required thickness for the Plastic is 3/32”.

References: Young [1].

Thermal AnalysisAlong with a structural analysis, a thermal analysis was also performed to ensure device safety and durability. A one dimensional steady state heat transfer calculation was performed using a thermal circuit approach with a heat generation of 3 watts, and yielded a maximum case temperature of 48° C. This was a very conservative calculation however, because it is very difficult to discern the heat generation of the circuit on paper, and the thermal behavior of the device would have to be verified in testing for a more accurate result. See note below.

Cross-Sectional Area:

Thermal Resistance:

Temp Equation:

Project P12036

Figure 5: Finite Element Stress Analysis for the Enclosure in Solidworks Express

Figure 6: Worst Case Temperature Analysis on Enclosure in ANSYS

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Note: This calculation assumes a constant heat generation due to the device operation being an “On” only state. In actual operation, the device will be flashing or pulsing between 1 and 3 Hz for no more than 2-3 minutes. By the nature of this operation, the above calculations are extremely conservative. Also due to the low thermal conductivity of ABS Plastic, it is unlikely that the case temperature will rise above ambient.

References: Incropera [2]

RESULTS AND DISCUSSIONEach portion of the product was tested independently. Every voltage regulator, for example, was tested for a

range of inputs. The indication LEDs and high-intensity LEDs were tested with their current-limiting resistors populated on the board. Correct functionality of the previously mentioned boards was proven via testing.

The battery regulator circuit was verified on a breakout board and a power supply. The output was as expected, charging up to 4.3V, and the battery was shown to have the current capability to run the device.

The MSP430 was connected and verified via test dongle included with the development kit. A simple program was loaded on to the chip, and it was able to drive a few indicator LEDs and the bed shaker.

A few pads of the PCB were inadequate; the inductor needed for the boost converter was much larger than expected. Leads were soldered to it, and it was fixed to the bottom of the PCB. One transistor pad was made assuming the wrong pin out. The piece was able to be rotated to avoid the wrong pad. The Molex connector pads were designed for 7 wires, but the Molex connectors themselves only can only be ordered in standard sizes, in this case 8. Several pads were SMT0402 and the parts we ordered were SMT0201. Each problem was not critical; most were able to be avoided by soldering them anyways. The PCB design file was updated to reflect these changes for the future.

The production method used for the housing didn’t allow for certain screw holes on the original CAD drawing. More specifically, the holes mounting the LED boards were horizontal with respect to the bottom of the case, which prevented the support material of the process from being properly removed. The case was redesigned to hold the LED boards in place with slots that the board slides into. The prototype process also didn’t allow for enough structure to screw directly into. We had to use threaded inserts to give the screw enough support to hold the case together without destroying the plastic.

The PAN1325 as currently connected and laid out on our board did not operate. This was due to the lack of required level converters between the I/O lines on the MSP and the difference in voltage levels that the PAN expects. The Bluetooth module needs 1.8V and 3V were being supplied which rendered the PAN inoperative. The addition of level converters solves this error. Using the PAN1315 ETU board, we were able to get our MSP and board to connect to the PC via Bluetooth.

The software application works properly, communicating with the device as required, and transmits all user settings correctly. The commands given to the device from the PAN and MSP430 are properly executed when the level converters are implemented. Alarms have been set, snoozed, and cleared properly, with the LED’s flashing and the bed shaker vibrating as set by the program.

CONCLUSIONS AND RECOMMENDATIONS

Several improvements could be made to the device. In phase three of this project, one of the first things that should be considered is the addition of small screen that will enable the user to see the set wake-up time in case the PDA or smartphone was turned off. The inclusion of high intensity LEDs along with a rechargeable battery rendered the team unable to significantly reduce the size of the previous device. Therefore, size reduction could be a priority for the next phase. Due to the fact that a new Bluetooth module was used in this phase the bed shaker had to be physically connected to the device. This new Bluetooth reduced the price but increased the programming level of difficulty thus only the device was wireless. In order to simplify the product’s usage the shaker’s signal should be transmitted wirelessly. Due to difficulty and time assembling the LED boards, we recommend that the LEDs are surface mounted and the boards be placed on the wall of the device. Because our product is a prototype, we had to design the case with that in mind, and also had obstacles because of it. Because the material isn’t structurally whole, screws couldn’t be affixed to hold the case top and the ON/OFF switch. The easiest solution is to make slots for the

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switch and the design should be reengineered to practices and manufacturing rules for injection molding. Injection molding will also eliminate the need for threaded inserts. Finally, improvements should be made to the snooze switch. As mentioned in the discussion, a tilt switch was used to implement the snooze function. This team considered the possibility of using a three axis accelerometer, but finally discarded it due to time constraints. Nonetheless, an accelerometer would enable the user to shake the device rather than tilting it to turn the snooze function on.

REFERENCES

[1] Young, Warren C., and Raymond J. Roark. Roark's Formulas for Stress and Strain. New York McGraw-Hill, 2012. Print.

[2] Incropera, Frank P. Fundamentals of Heat and Mass Transfer / Frank P. Incropera ... [et Al.]. Hoboken, NJ: John Wiley, 2007. Print 2008.

[3] MSP430 Datasheet http://www.ti.com/lit/ds/symlink/msp430bt5190.pdf[4] PAN1315 Datasheet http://www.pedeu.panasonic.de/pdf/174Datasheet.pdf

ACKNOWLEDGMENTS

Special Thanks: Dr. Gary Behm (Costumer) Professor George Slack (Faculty Guide) Dr. Dorin Patru Dr. Adriana Becker-Gomez Dr. Elizabeth DeBartolo Christine Hartman Jeffrey Lonneville

Project P12036