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<br><br>[[Image:GPSunit.jpg|left|300px|GPS Unit]]
<br><br>[[Image:GPSunit.jpg|right|300px|GPS Unit]]
==Executive Summary==
==Executive Summary==

Latest revision as of 17:08, 3 March 2008

GPS Unit


Executive Summary

Global Positioning Systems have been used for the past thirty years. They were initially intended for military services but now have recreational purposes as well. Basically, the GPS system operates by using a system of satellites and receivers. The military uses the GPS to track their troops and plan movements more efficiently. However, uses of global positioning systems are much more widespread now, most commonly as navigation systems in cars. There are many more uses for GPS units, which will be discussed further.

Our report details the mechanisms that the unit uses to provide the measurements of position, velocity, and time. The introduction will outline our page. We will also describe our GPS unit, as well as its capabilities and limitations. Next we will discuss the accessories that come with the GPS unit. Our wiki page will then describe the unit before, during and after disassembly. Within this section we will discuss the various parts. During disassembly, we will pay close attention to the difficulty level and precaution taken at each step. Finally, after re-assembling the GPS, our group will discuss if the unit is still working accurately.


The project was completed by William Haydt, James Therrien, Chase Howard, John Dean, Brian Stouffer, and Elizabeth Holly of Drexel University in Philadelphia, Pennsylvania. William Haydt, James Therrien, Brian Stouffer, and John Dean took apart the device and logged all parts. Elizabeth wrote the "Executive Summary" section. John wrote the "Indroduction" section. Chase wrote the "Before Disassembly" section. William, James, and Brian wrote the "General Accessories for GPS", "Disassembly Procedure", and the "After Disassembly" sections.

The purpose of this project was to understand the DeLorme Earthmate GPS PN-20 unit and also understand how the system works. We chose to disassemble the unit and describe each component in the entire unit.

The PN-20 is a waterproof hand-held GPS unit with the ability to show current positions on a map, aerial photography, USGS Topo maps, DeLorme Topo maps, and satellite imagery.

Before Disassembly Section

The DeLorme Earthmate GPS PN-20, in new condition, is housed in a waterproof, impact-resistant rubberized casing. The unit’s dimensions are 2.43” W x 5.25” H x 1.5” D and it weighs 5.12 ounces. It has 75 MB available storage for user-uploaded maps and a proprietary Kalman filter for enhanced GPS accuracy. The unit is accurate to within 15 meters and has a 0.05 meter/second steady state velocity accuracy. The STMicroelectronics chip technology with SiGE front-end and DeLorme’s firmware allows for faster acquisition times and exceptional signal retention. The warm acquisition is about 15 seconds and the cold acquisition time is approximately 60 seconds. Two AA batteries are used to power the unit for up to 22.5 hours of use or it can use an included travel power kit. The unit’s display is a sharp high-resolution 2.2” transflective TFT color display.

The Earthmate GPS PN-20 can store waypoints, tracks, routes, and the base map data in its internal memory. Maps can be saved to the internal memory or the removable memory card. The unit can be used to save or gather information about a map object, such as name, latitude and longitude, elevation, and additional comments. Objects can also be marked and saved as waypoints.

Chase Howard
General notes about the product (it's condition, how it works, how many parts, types of materials, etc)

General Accessories for GPS

  • Safety Strap- This device allows for the GPS unit to be safely carried without dropping it. The strap firmly attaches to the GPS unit and loops around the users hand. The strap then has a slider that can be pulled up to the wrist to tighten the strap to the users wrist size.
    Safety Strap
  • GPS Charger with Outlet and Car Extensions- These accessories charge the battery of the GPS unit. They allow for charging anywhere that an outlet is accessible, or for charging in the car through the cigarette lighter.
    GPS Charger
  • USB Connector- The USB Connector is used to transfer data and information to and from the GPS unit. Data recorded can be uploaded from the GPS to a computer and vice versa.
    USB Connector
  • Portable Package Kit- Contents included various charging equipment for the GPS unit. These contents were; 8-pin-to-Mini-USB Connector, Lithium-Ion Battery and Charger, LCD Protective Film, A/C Adapter, USB to Mini USB Cable, 12-volt Adapter for Lithium Ion Battery Charger.
    Portable Package Kit

William Haydt

Disassembly Procedure

Back cover.jpg

The first step in the disassembly process we took was the removal of the back battery cover. To do this there are two screws that can be removed by hand since there were metal loops attached to them as shown in the picture to the left. These metal loops are there for the wrist safety strap, but are large enough for the user to manually grab and turn the screws. This step is required for the operator to do since the back cover holds in the batteries. Therefore the difficulty of this step is very easy and requires no tools.
James Therrien

Battery slots.jpg

After the removal of the back cover, there is an opening left where the batteries of the GPS unit are located as shown in the picture to the left. Also this picture shows the location of where the usb connector for file transferring to a computer. In the picture it is the eight small metal sensors at the top of the unit.
James Therrien

Back cover removal.jpg
The next step taken in the disassembly of the GPS unit was the removal of the back half of the enclosing case. This step must be completed from the back of the unit since the heads of the eight small screws are located there. In order to get to four of these screws, a small Philip's Head screw driver must be used since the screws heads are embedded in holes in the outer case and not directly on the surface of the case. The screws do not need to be taken out in a specific order but a thin screw driver is necessity for removal. This step was also fairly easy and the amount of caution that is needed for this step is minimal.
James Therrien

Back seperate front.jpg
After the screws are removed and the back half of the case is separated from the front, the only connection between the two are a series of wires that can be manually disconnected by hand. This step requires no use of tools, but must be done carefully since the mechanics of the inside of the GPS are fragile. There are three separate connections that need to be removed. The picture to the left shows the back of the front half of the unit, the 1GB memory card and the computer reading accessory. The memory card is slid into the cover of the memory card slot so that the metal strips of the card is faced out.
James Therrien

Faceplate and motherboard/Screen

The next step in the disassembly process is to remove the Motherboard from the encasement. This is acomplished by removing two additional screws that hold it in place. Once these are removed, the mother board and attached LCD screen can be lifted easily from the casing. The picture shows the front side of the motherboard that is pictured in the previous picture. This motherboard holds all memory and function of the GPS and therefore must be handled with care.
Brian Stouffer

Gasket and Back of Faceplate

The natural progression is to now remove the gasket and rubber buttons from the front encasement. This gasket is not actually connected to anything at this point. It is simply shaped to fit snug onto the encasement. Notice how the protruding rubber buttons corrispond to holes in the front plastic. These fit together and actually protrude from the front of the GPS when assembled. They are the exterior buttons that are used to control with the GPS.
Brian Stouffer

Backside of LCD

In this picture we have once again concentrated on the Motherboard and LCD assembly. As you can see, the LCD screen has been partially unattached from the Motherboard and flipped over to show seperation. The LCD has clips on eather side that fit tightly around the Motherboard. It does not require a tool to remove these clips. It can be done by hand. There is one large ribbon style wire connecting the two components that does not detatch.
Brian Stouffer

Frontside of LCD

This is an additional picture showing the reverse side of the picture above. Notice the LCD Screen and the motherboard.
Brian Stouffer

After Disassembly

Parts List
Part Name Number of This Type of Part Part Material
1/8" Screws 4 Steel
1/2" Screws 4 Steel
Motherboard 1 Primarily plastic, but both copper and steel components are soldered onto the motherboard for proper operation.
LCD Screen 1 A glass face with stainless steel bordering and plastic backing. Its innards are common to the motherboard, primarily plastic with copper and steel components.
Gasket 1 Rubber
Outer Case 1 Plastic

James Therrien


  • The Assembly of the GPR is simple to complete. If the components begin disassembled like they are at the end of the Diassembly section, assembly can be accomplished by following the steps from that section, in reverse. The first step is to connect the LCD screen to the Motherboard. These two pieces slide and snap into place with the use of the hands. The step is simple and takes only a few seconds to complete. Set this piece aside and continue.
    Brian Stouffer

  • Now take the Front Encasement and the Rubber Gasket/Buttons and place them together. There are no connectors that hold these two pieces together. They simply fit tightly to one another by a rubber design that matches the plastic perfectly. Lay the aparatus facedown to prepare for motherboard attachment.
    Brian Stouffer

  • Once you have completed step one and two of the assembly, the two pieces that you've created are ready to be attached to one another. With the encasement and gasket facedown, place the Motherboard and LCD Screen on top, making sure to match the LCD to the clear plastic section of the encasement and the buttons to the button sensors. You will know that these are in place when the two sets of screw holes are alligned. There are two screws that need to be screwed into place to hold these two sections together. You will need a small screw driver to accomplish this.
    Brian Stouffer

  • After screwing the motherboard back into the front encasement, the three multiple wire connections need to be reconnected. This step is easily done without the use of any tools, but must be done with some care since it does have to deal with the unprotected hardware of the GPS unit. These connections simply clip into place when a slight force or push is applied.
    James Therrien

  • The next step of re-assembly is probably the most difficult. In this step we are going to put both halves of the GPS encasement back together and seal the hardware. It requires the use of the long, thin shafted, small tipped, Phillip's Head screw driver and patience to align the gasket properly. Upon closing the casing, if the gasket is not aligned correctly or shifted in this process, the hardware will not be protected as well from outside elements such as water or dust. Also, if the gasket is not matched up with the screw holes, when the two halves of the GPS encasement are put together, it will block the screws from fastening the case together and will cause problems. You may tighten these eight screws in any order, but they must be snug.
    James Therrien

  • The last step leaves you with a fully covered GPS unit with only one more step to complete its reassembly. This last step is the attachment of the back battery cover. It is a simple step that can be done by hand, by screwing the two screws into their respective locations on the back of the case. The screws have little metal loops on them so that an easy grip can be achieved. These screws should also be tightened to hand tight, and not necessary for any further torque.
    James Therrien

After Assembly

  • It Still Works!

Despite the disassembling of the GPS unit, and our groups lack of experience doing anything like this before, we managed to put the unit back together and have it work at full capacity. It's not often you are trusted to do this type of project, and we are just thankful that along with the knowledge we gained, we also do not owe Dr. Cheng $500.00 for a new GPS! Once the unit was all back together, we ran through some uses of it and made sure that we had a working unit that did everything it did before we performed our "surgery" on it.

  • Concluding Remarks

This project was a very intriguing one. It's not often you get a project to do with such autonomy to it. We decided that probably the most interesting thing to do with the GPS unit was the suggested disection of it. We weren't disappointed either. It was amazing to us that despite the amazing capabilities of the unit, it was no more complex than that of an old model Nokia cell phone excluding the computer. Like we said before, it's not that common to be able to play with the inner workings of an expensive piece of equipment and this project allowed us to do that. Along with the disassembling of the GPS unit, that WIKI facet was a great part of the project as well. Getting to present the information we recorded in a coded format on a web page is an interesting way to show what you have done. It was a little bit tricky for us but we learned as much about WIKI as we needed to present an effective project. Overall we would say that this was a successful project and should be continued.

William Haydt


1.Earthmate GPS PN-20 with Topo USA 7.0 & 1 GB SD Card & Reader Bundle
APA Style You must use this format (It's easier than MLA, so don't worry).

Guide to Writing Wiki Code

The beauty about Wiki is that if you don't know the code, you can steal it from someone's page that does. Feel free to click the "edit" links or tabs to view the code for sections or the pages respectively. Be weary about wrecking havoc on another's page. Each page can be rollbacked to a previous verison and your username is linked to all changes. Although you might think it's cool to go through and insert "MIKE RULES" throughout the page, I'm sure Dr. Lewis would not be pleased.

Here's a few tips on writing with Wiki:

This is a bracket "[" "]"

This is a brace "{" "}"

To create a new page/link within Wiki:

  • Double brackets, page name, double brackets
  • Typing in a new page name will automatically create a page, which when clicked, you can then edit.
  • Whatever name you first type in is the name of the page. You can't change page names, only create new pages. Think before you create a new page.
  • Don't worry about slashes or anything, all pages are located in the same directory. If I wanted to create a page called "MAE 277 Template" the code would be ''MAE 277 Template'' Note: Brackets are italicized to prevent creating a new page.

Your table of contents is created automatically.

  • 1,2,3,4 are level 2 sections
  • 1.1, 1.2, 1.3 are level 3 headers

To create headers:

  • Section titles are wrapped with two equal signs ==My favorite header==
  • Bold headers within a section are wrapped with three equal signs ===My not-so-favorite header===

Asterisks indicate bullets. Be sure to put each asterisk on a new line.

  • Here's one
  • Here's two *Here's three, but its not on the next line

Bold text:

  • Start line with "b" in "<>". Be sure to end the line with "/b" in "<>" if you don't want the whole paragraph to be bold.
  • Surround text to be bolded with three " ' " marks on either side. Or highlight the text and click the "B" button on the toolbar.


  • "i" in "<>". Don't forget to end with "/i" in "<>"
  • Highlight the text and click the "I" button in the toolbar (It will put four " ' " on either side).

This is a broken link media file caption

Media tags are indicated by "Media:", images by "Image:" Broken links in red. Case is not important. Use the toolbar to get examples if you're not sure.

Spacing is werid in wiki. Single return does nothing.

Double return (blank line), breaks the line.

Triple return (two blank lines), puts an extra blank line between lines of text.

"br" in "<>" will break lines. They can also be used to separate section headers.

Finally, use the "Show Preview" button on the bottom of the page to see how it looks before saving. It will allow you to catch and edit your errors without having to edit the page again. Just don't forget to save it when you're really done.