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Thursday, June 26, 2008

First design of the housing

Top view:
Bottom view:

I have completed a first draft design of the housing. Here are a few comment on the housing:
  1. Take a close look at the Apple design of your dock connector. I have managed to take that connector apart without destroying it. It's a pretty sleek design, consisting only of two parts: a sleeve that goes around the connector and a cap that slides over the connector and inside of the sleeve. I have made the housing for the GPS module in a similar rounded/flat shape as the Apple sleeve. Apple's sleeve is 26.1mm x 9mm x 5.6mm (width x length x thickness). The GPS module housing is 25.4mm x 22.2mm x 8mm. So it is a little thicker as the dock connector and about 2.5 times as long.

  2. You can see the micro USB connector on the left side of the module (top view).This plug can either accept micro USB-A or micro USB-B cables. I have found a trust-worthy supplier for the micro USB-B cable and the cable will be included with the GPS module to make life easy :).

  3. On the top view you see a small green light. This is the LED indicator that displays the status of the GPS module: flashing orange means the module is searching for a satellite lock. Once a lock is found, the indicator will light steady green. My plan is to make this indicator aperture similar to Apple's MagSafe power adapter that is used on the MacBook.
In the meantime, I am playing with some more ideas to make the housing design even simpler...

Friday, June 20, 2008

Board and chipset update

This is a brief note to give you an update on the board assembly that I started last week.

It turned out that the problem of the GPS chip not sending data was not in the GPS chip itself but caused by my own mistake (:-o). I was trying to get the module together quickly to test the new board, and in the hurry, I didn't solder one of the components onto the board, which left part of the GPS chip disconnected. After a very helpful phone conversation with the chip vendor, we traced the problem down in 5 minutes.

I guess sometimes it is indeed good to take a brief break from everything and let things come to peace; after I soldered the missing component onto the board, everything worked flawlessly :)

And I have another update for you: the next chip-sets that I ordered will be A-GPS enabled!

Wednesday, June 18, 2008


As a few questions were posted earlier regarding A-GPS (assisted GPS). I will try to outline the differences between regular GPS and A-GPS.

A GPS module is dependent on the GPS satellite signals to find a fix. The weaker this signal, the longer it will take to get a fix. If too weak, no fix will be found at all.

  • When a GPS module is first turned on, it will usually have no satellite position data (ephemeris). This is what is called a cold start of the module (assuming the module does have a valid almanac stored). It is then necessary to place the module in open sky to have it acquire satellite data. This can take anywhere from a minute to several minutes, sometimes even longer, depending on the satellite signal strength, surroundings and the sensitivity of the GPS module. This sensitivity of the GPS module typically ranges from -140dBm to -146dBm for a cold start (the more negative the number, the more sensitive the module is).
  • Once a GPS lock has been obtained, the GPS module will store this recent satellite data (ephemeris, almanac and time) in its memory and the module is said to be in tracking mode. When in tracking mode, the sensitivity increases as the module now has satellite data available. Typical tracking sensitivities are from -155dBm to -160dBm.
  • If power is cycled off on the GPS module, then fairly immediately back on, the ephemeris data is still "fresh" (but the time might not be), and a GPS lock will be very quick since the GPS module does not have to collect new ephemeris data. This is called a warm start and the time to fix is typically less than half a minute.
  • If the GPS module also still has an accurate time, the fix will be even faster (usually on the order of a second) and this is called a hot start.
In general, if ephemeris data is not available or outdated, obtaining a GPS lock can take some time. This is where A-GPS can help.

An A-GPS receiver can help getting ephemeris, almanac and time data from an assistance server. The assisting data can either be downloaded every time the GPS module is turned on (e.g. through the GSM network or WiFi) or in advance (e.g. once every 14 days at home from the internet). In the first case, ephemeris data, almanac and time are downloaded. In the latter case, differential almanac correction data is downloaded.

In order to be able to use A-GPS, we need three things:
  1. A chip that is A-GPS compatible, i.e. the chipset allows for download of assisting data to the GPS module,
  2. An assistance server from where the assisting data can be downloaded. Assistance servers are usually provided by GPS chipset manufacturers and need to be mirrored for client usage. (Apple is probably mirroring Broadcom's servers for use on the 3G iPhone).
  3. A way to upload the A-GPS data to the GPS chipset. This can usually be done through a software download daemon which both acquires the data from the assistance server and sends it to the GPS chip at certain time intervals.
So A-GPS can make your GPS module find a faster lock, typically increasing the cold start sensitivity to about the level of a hot start.

It needs to be mentioned however that if a satellite signal is simply too weak (e.g. <-160dBm in parking structures or big concrete buildings), you won't see any improvement at all in the performance of your GPS module, even if you have an A-GPS enabled chipset as the GPS receiver won't be able to receive any signal even though you tell it were the satellites are.

Regarding the GPS chipset that I am using, the chipset can be enabled for A-GPS use and assistant data could be downloaded to the module through the serial port if the data can be obtained from an assistance server.

Sunday, June 15, 2008

The Return of the Boards (part 3)

As you can see in the photo, the two boards that were sent out a while back have returned!

Also, before we discuss the boards, we hit 1500 votes this week as well (and that despite all the distracting iPhone 3G buzz) !

Regarding the boards, I started assembling one board last Thursday night but ran into problems testing the board. It took me two nights to debug the problem. The boards seem to be oke; the GPS chip I am using is the same as the one on the prototype II boards and it functions there without problems. I suspect the problem is in the GPS chip itself: although all output voltages seem oke, no data is transmitted. I had a spare unit which I tested off the board and this one has the same problem. I will have to contact the manufacturer to see what the problem is and to get functional replacement units.

Well, I guess things can't always go smoothly. I am sure we will recover quickly from this after I get new functional chips. I'll keep you updated once I find out more from the manufacturer. This shows that you always need to double check your suppliers, especially when you are using their latest technology. It also shows that it is a must that every single unit that gets shipped is quality controlled. In fact, I will guarantee that every GPS module that I will ship, will have been inspected and is 100% functional. Or as we say in dutch "De klant is Koning" (literally translated as "The customer is King" :).

In the meantime I have also been working on housing related things this week: I have pretty much completed the 3D modeling of the most important parts on the board (which will be needed to make sure that the housing doesn't interfere anywhere on the inside with the board/components). Also, I have already outlined the housing itself. Detailing of the inside will be next.

Tuesday, June 10, 2008

iPhone 3G buzz....

After having read some of the discussions on the previous post, I think it might be good to speak some sobering words and try to see things in perspective.

  • The new iPhone is extremely cheap, even cheaper than an 8GB iTouch..... BUT you will have to sign a two year contract with AT&T (see here) for most likely a minimum of $39.99 a month.... or sign and then break the contract and pay the termination fees (probably around $200). So that puts the price tag right back at $399. My guess is that AT&T is subsidizing Apple those $200 for every phone sold.
  • AT&T is still the exclusive U.S. carrier...
  • Rumors are going around that you won't be able to buy an iPhone without signing a contract, either in the Apple Store or the AT&T store (see here)
  • Regarding the iPhone 3G itself, how many of the current iPhone users would actually upgrade to the new model? Most likely those users who are already with AT&T and who are willing to spend the additional $199. I would guess that for most of the hacked phone users (who don't wan't to be with AT&T to start with), dishing out $199 + cancellation fee would be a little over the top.
  • Steve mentioned that around 6 million of the original iPhones were sold. It was estimated that around 750,000-1 million phones were hacked at the end of Jan. 2008 (see here) and maybe it is even up to 20-25% now. How many of these phone users would want a plug-in GPS module? Even at less than 1%, it would be worth to make the effort.
  • Note that even today after the announcement, iPhone users have been voting that they still would like a GPS module.
  • Lastly, don't forget the iTouch users. The iTouch doesn't have GPS (at least for the time being), so who will take care of them?
So to make the story short, I will keep on doing what I have been: working hard to come out with a GPS module for iPhone and iTouch users at an acceptable price and as soon as possible.


Sunday, June 8, 2008

Compatible? YES!

Link for iPhone and iTouch users here.

Just recently, a GPS plug-in for the was released by xWaves. The video above shows how my GPS module also works with that software.

The source code for the software was released as well and can be found here and checked out with regular svn. All credit for this software goes to the people at xWaves.

Below is some more information on how the software works:
  • The software currently talks to the GPS module directly through the serial port. The standard baudrate is 19200 which I had to adjust to match my module. It will be best if the software is updated in the future to automatically check what baudrate the GPS module is running at. Another option is to add in functionality to work with a gps daemon.

  • The xGPS program is a daemon that runs in the background and is started through a plist file in the Launchdaemons directory. This deamon talks to the and the serial port and tells the to update its location with the data obtained from the serial port.

  • The software currently needs to connect to the internet to update the map as it calls the Google website to update its location. It would be nice if someone figures out how to circumvent this and have the update its location directly from its database without having to connect to the internet. In that way you could upload your own maps to your iPhone/iTouch and use those while on the road.

Then finally one comment on the video. I stated: "...the GPS module is charged through the USB..." What I actually meant to state is that the iPhone is charged through the USB. If you look closely, you can see the charging sign in the video.

Then lastly, before signing off for tonight, I also wanted to let you know that I am currently working hard on the housing design and getting manufacturing for the boards set up.

Sunday, June 1, 2008


I had a busy week. I have frozen the board design and sent out two PCB designs on Friday.

Both boards have the same functionality, but one of them is pushed to the smallest limit in terms of size (15.2mm x 23.4mm, see the left side of the photo). It will have to be seen if this board can be manufactured and assembled automatically with components. In case not, I have the second PCB design which is a little bigger (17.7mm x 23.4mm, see the right side of the photo) and which should not have any problems for fully automatic manufacturing and assembly.

I will be spending the next couple of weeks on the mechanical design of the package. This package will be based on the larger board. The two PCBs have been laid out in a smart way such that both will fit in the same larger package.

If it turns out that the smaller board can be assembled automatically (or if hand assembly of one or two components is not a problem), then the mechanical package can be shrunk in size by just changing one single dimension of the package! That's why it took a little while to come up with the current frozen board design.

You can also see that I have redesigned the website slightly and re-arranged some things: posts in the center, polls and the blog archive in the left side bar, and my human rights related links in the right side bar.

Upon request, I have also added a donation button on the left top for anyone who wants to donate. In addition, I have added some Adsense ad-links throughout the page. I have noticed that they are quite on the topic of the blog and they will also bring in a little bit of revenue when people click on them.

I am glad I was able to get this final board design out the door before the end of May :)