Introduction: How to Assemble an SMD GPS Device - OHARARP LLC

SD GPS Data Logger -

I am a small developer of embedded soultions for all types of applications. One my personal interests is with GPS positioning products. To satisfy some previous patent work I was doing I needed a device that would record large amounts of gps data (lots of memory) over a long period of time (big battery) and was compatible with mac's and pc's. Unfortunately, nothing of this sort existed and I had to create a device to do this.

This product is the culmination of implementing a number of new designs for myself. Mainly, using surface mount components, lithium ion/polymer batteries, and Sandisk SD memory cards.

Since so many electronics parts are surface mount these days I needed to use these components but was a little bit fearful in making the leap from using through hole/traditional soldered parts. Sparkfun Electronics helped my learning with their tutorials and I thought I would continue the tradition through an Instructable.


Picture 1. Place circuit board where it can be held securely
Picture 2. Tape Top of acrylic stencil to board; make sure it is properly aligned over the pads of your pcb.
Picture 3. Using your preferred solder paste apply a good sized glob to a simple plastic paint spreader
Picture 4. Spread the solder past liberally over your acrylic stencil. Make sure to cover all the holes!
Picture 5. In the next 2-3 passes try and remove as much solder paste from the stencil as possible.
Picture 6. You should have almost the same amount of solder paste your "spatula" as you began with except for the holes in the stencil.
Picture 7. After carefully pulling up your stencil and removing the pcb you would repeat this process for the next board. When complete be sure to remove all solder paste from the stencil. I prefer windex and a toothbrush to clear out soem of the holes for really tight pitch components.

Step 2: PROGRAM PIC 18LF4620

This design has its firmware locked into the ic and is only programmed at the time of manufacture.

Picture 1. We are assembling 15 boards today. Here you cansee 12 of the Pic 18LF4620 uProcessors that are used.

Picture 2 & 3. We place each part in a special adaptor that is tied to an serial programmer.

Picture 4. The firmware is downloaded via a pc using the melabs meProg software.


Picture 1. You can clearly see that there is a nice bit of solder paste on all of our pads. Using a nice set of tweezers ( I place all of the components by hand.

Picture 2. Here I have placed the uPic and you can see how nicely things are lined up. This is where a good set of dental needle tools come in handy ( It looks like the solder paste might bridge between the ic legs. However, there is just the right amound of solder paste that when we heat the board up these bridges should not appear. If they do a quick application of heat from a soldering iron and copper solderwick will fix this.

Picture 3. Step and repeat until you place all of your components.


So my wife is pretty pissed that she can't make pancakes anymore, but now I can solder all my boards quickly and easily!

Picture 1. This griddle tops out at 400+F for temperature. I set it to max and let it heat up. After 5 mins or so I apply as many boards as possible on the griddle.

Picture 2. More of the same, just a little closer. Make sure you have plenty of ventilation as the fumes from the solder paste are toxic. It can get stinky pretty quick! I usually place a box fan in front of a window and draw the fumes outside.

Picture 3. After a few minutes you can clearly tell when the solder has melted. Some cold spots may appear on your griddle or larger parts may not always reflow. I have a hot air rework gun handly to help out the usb connectors.


This step should be helpful to alot of people trying to add li-ion or li-polymer power to their design. It is of EXTREME importance that a rechargeable lithium battery have protection circuitry. Your cell comes with this built into the package of the battery by the manufacturer. We purchase bare cells from and highly recommend their Protection Circuit Modules (PCM). They basically work to isolate the dround of the battery from the rest of the circuit when a fault condition is encountered. This is especially handy in case you short something on your board. The power in the battery will quickly "vaporize" your copper power traces!

Picture 1. Battery and PCM
Picture 2. Battery and PCM assembled
Picture 3. Add a nice heat shrink wrapping for protection
Picture 4. Place foam tape on pcb to help hold battery in place
Picture 5. Foam tape peel removed.


We are nearly complete...just need to add the final casing. Because the 18650 battery is slightly larger than the case depth we have to add some .125" acrylic spacers that are manufactured by

Picture 1,2,3. Remove the protective paper from the acrylic pieces.

Picture 4,5. The case must be slightly machined to account for the additional height of the usb connector and power switch. This is done using a wood router table.

Pciture 6,7. Add 4 4-40 screws, acrylic pieces and circuit shell case and VOILA!


james.mcglashan made it!(author)2009-05-28

does this have a screen extention ???

ohararp made it!(author)2009-05-28

james no screen on this device. Total passive logger.

james.mcglashan made it!(author)2009-05-29

ok pitty lol it should have 1 so u can use it as a gps.

collard41 made it!(author)2008-08-22
$175!!! i bet the components only cost $50, mostly for the battery and the GPS module. do you think you could post a picture of the schematics. or something.and also, when you connect it to your computer, does it send coordinates, and speed and direction, or do you have to work them out yourself.i have to say, i agree with the people who say that this is geared to advertsing
myozone made it!(author)2007-08-28
ohararp made it!(author)2007-08-30

To bad the logger only logs for 8 hours. They are using a lot of power for their device. Not sure why. My design only requires ~58 mA and can run for ~48 hours continuously. We also implement a sleep mode that draws <1mA. Oh, and the product isn't available yet nor does it come with an SD Card.

myozone made it!(author)2007-08-31

Hello, yes indeed your's looks to be a better option, I was mearly pointing out that there are other options.

ohararp made it!(author)2007-08-07

Chavez, I typically use matlab to sift through all the data and would be more than willing to share this code. The easier route is to upload the files to This is the gpsbabel for the web! Its great for all types of formats.

ohararp made it!(author)2007-08-06

You wouldn't believe ow many e-mails I get about people being afraid of using smd components. Sparkfun posted something similar on their website to this instructable. It prompted me to go out and MAKE things. I wanted to address a couple of things in this instructable: 1. Show that normal people can make things using smd components. If you feel particularly interested you could even start a business. 2. If you are going to use li-ion batteries in your project you should always use a protection circuit module (pcm). 3. Finally, I wanted to show the whole process of pcb's, smt parts, enclosure, etc. A lot of instructables out there are "hacks" and that's great but not many people show how a product could be made applying just a bit more thought than say "fixing some headphones".

johngomm made it!(author)2007-08-07

Re-reading the article, I think the SMD process could do with a bit more detail. For example, the acrylic stencil you refer to is not clearly shown or described. How do you make the stencil? Are there tricks to ensuring the right amount of solder paste? Would you recommend this technique if you were doing small runs of <20 or is it better to hand solder, as I've seen other people do with SMDs? I like most of the introduction you have now, but Chavez does have a point that it does have a hint of an advert to it. Maybe if you sold a home-solder parts kit with circuit board, this might change the tone.

ohararp made it!(author)2007-08-07

John, Thanks for your constructive input! I took out the last part of the intro. Really, this is meant to be helpful. I will try and add a bit more info on the stencils. Being that they are thin clear acrylic they don't photograph well. Heck, I might just make a separate instructable on this process. I like your idea about the home solder kit too! Now that could be a helpful product that no one is really offering right now. If a kit like this were available what would you want it to do? I figure it would have to have some blinky lights for sure! Maybe a SMT POV project?

ohararp made it!(author)2007-08-06

Hey all thanks for the input. I tried to make a few changes to help introduce everything. To help answer your questions John: 1. Price is $175 2. We considered an LCD but wanted to keep power draw as low as possible for maximum runtime. For instance, a # of customers use them for animal tracking over several months. 3. I prefer for most of my parts...They have a great "projects" page that keeps track of all your parts for a particular project that is really helpful. 4. With the datasheet I include a schematic. Otherwise, I have released some previous source code, but like to keep that part for me. However, I do modify the firmware for customers, usually at no cost for their particular projects.

johngomm made it!(author)2007-08-06

How much would one of these cost? Would it be easy to add a read out lcd so one could know where you were in real time without attaching a PC? What's your favored source for components? Are your designs open for user modification? I agree with dchall8, it would be great to have that little explanation up front in your instructable, so people have their curiosity peaked before they wade in to technical surface mount details. Other than that, nice photos and pretty clear instructions. Good job.

dchall8 made it!(author)2007-08-05

I'm starting to sound like a broken record. Please explain what you're talking about. Start by spelling out SD GPS. I think I know what GPS is, but maybe not. What does this do? Why or when or where would I want one? Why would I want to log it and what's smd?

computer_gui made it!(author)2007-08-06

Secure Digital (SD) is a flash (non-volatile) memory card format developed portable devices, including digital cameras, handheld computers, PDAs and GPS units.

The Global Positioning System (GPS) is a fully functional Global Navigation Satellite System. Satellites transmit signals that enables a GPS receiver to determine its location, speed and direction.

Surface mount technology (SMT) is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards (PCBs). Electronic devices so made are called surface-mount devices or SMDs.
(definitions were from

This device would gather GPS data and store it on the SD card so it could later be uploaded to a computer to determine where it (and also who/what its attached to) has been. There are many different uses for such a device, parents (or employers or the FBI) often use them to track where (and how fast) there child (or employee or suspect) has taken their car. Some people also just like to know where they have explored or how fast they biked or how far they ran.

dchall8 made it!(author)2007-08-06

That's not what I thought at all. Now I want one.

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