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Saturday, May 24, 2008

I/O connectors

Since quite a few people were concerned about the USB connector, I am writing a short summary of the I/O connectors that I have looked into (see the photo)

  • 30 pin Apple dock connector (left bottom): best solution, but due to its large footprint it gives a rather large board when combined with a patch antenna. The prototype II board combined this connector with a chip antenna while providing a small board size, but the performance of the chip antenna turned out not to be as good as a patch antenna.

  • 10 pin I/O connector (left top): next best thing considering it has 10 pins and allows routing of other signals besides the 4 and 5 pin USB connectors. However, there are no standard cables around that can plug into this connector and they would have to be custom molded.

  • 4 pin mini USB (second column from left): this is the connector I used on the prototype I boards. It has the smallest footprint among the mini USB series connectors.

  • 5 pin mini USB connectors (third column): this connector is the most commonly used on the mobile equipment of the recent past. It comes in different form factors (see photo from top to bottom): midway mount, bottom mount, top mount. It has a larger form factor then the 4 pin USB.

  • 5 pin micro USB-B connectors (most right column):this connector is the new standard for current and future mobile equipment and has quite a lot smaller footprint than the mini USB connectors. It comes in multiple form factors, two of which are shown in the photo: midway mount, top mount.

Regarding the mini USB cables, these are readily available these days from various places: 4 and 5 pin mini USB at Amazon, various USB connectors at Pricewatch, or just Google for mini USB.

The micro USB cables are a little more recent, but you can also get them from Amazon for $2, or from Walmart for $5.

So I don't really think it matters too much from an availability/cost standpoint what connector we choose. I might even make the cable available with the module. More important are other factors like footprint and height on the PCB.

As such, I have set the top-mount micro USB connector as the device of record (DOR) as it has the smallest footprint and lowest profile.

In the meantime, I will keep an eye out for any other low-profile multi-pin connectors that are around.

Feel free to post any more comments you have on the subject.

Sunday, May 18, 2008

More votes, more prototypes, more testing....

We hit 1000 votes today! This confirms that there is definitely enough interest in the module to keep on going full speed ahead :)

This week I have been busy building more prototypes. I had already built three with the old board and I have built another three this week. Prototyping goes a little faster now that I have the SMT rework station.

I have assembled two of the prototype II boards with a chip antenna (see the bottom two modules in the photo) and one of the old prototype I boards with a thinner patch antenna (see the right module in the middle row in the photo).

I have done some more field testing (that is inside, outside and in my car while on the road) and it does seem that the patch antennas work better than the chip antenna. The chip antennas also are very sensitive to board layout. I had to trim some of the copper on the board before I finally got these two chip antenna boards to work.

So I have decided that it is best to go with a patch antenna solution to guarantee performance. As such, there will be no room for a full dock connector but instead there will be a micro-USB connector which has a slimmer footprint than the mini-USB connectors and which is the new standard for mobile devices.

I also have an update regarding the LED indicator light. The prototype II boards have a bi-color blue/red LED. The blue LED is the power-on indicator and the red LED will flash until a GPS lock is found (combined with the blue it gives a pink/purple colored flash).

This week I will be working on the layout of the final board design for the patch antenna prototypes and I hope to have the board design frozen before the end of May.

Saturday, May 10, 2008

The tools of the trade

This post is especially dedicated to those fans who pretty much visit my blog daily!

In order to do a good prototyping job, you need good tools. So this is what this post is all about. For some tools, you can get away with the cheap stuff, for others, you can't cut any corners and just need to spend the money.

The photo shows pretty much all the tools that I am using for the prototyping:

  • A good quality solder iron that has temperature control and tips that can be changed. Mine is in the top right of the picture and it is a Weller WES51. I got it from my local Frys store for $100. You can get it online from their website as well. You can go the extra mile and find a station with a temperature sensor inside of the tip and tips that don't oxidize, but it's not really a necessity. Just make sure to keep that sponge wet and the tip wiped and clean.
  • As mentioned earlier, I had to order an SMT rework station to handle the new board and the more advanced parts. It is on the left in the photo and is a Madell Quick857D. It runs about $200 including tax and you can order it directly from the Madell website. Combine this tool with your board, solder paste and your parts, and you have a superfast assembly of your prototypes.
  • Then you will need the regular soldering supplies: lead-free solder (everything needs to be RoHS compliant these days, and make sure to pick the no-clean type), solder paste (if you have a SMT rework station), solder flux (no-clean), and solder wick. Check the Kester website for info on lead-free soldering supplies.
  • You can't get by without a digital multi-meter. You can go cheap here. I have a cheap $5 CEN-TECH P30756 which I bought ages ago and it still works. Just make sure to turn it off after use to save the battery. You can get yours at Harbor Freight Tools for a buck less.
  • While at Harbor Freight, also grab a pack of cheap pliers for $6, a pack of cheap tweezers for $6.50 and a precision knife set for $10. Also pick up a 6inch digital calipers for $20. For calipers you usually want to go the better more expensive brand, but mine was on sale for $16 so I decided to try it and it seems to work very well.

Now, sometimes I ask myself, how come some of this stuff can be so cheap? Apparently most of the tools are made in China nowadays and who knows who produced them: a legitimate company with reasonably well paid employees, or innocently imprisoned slave laborers/kids working 16-20hrs shifts. When it comes to these things, I at least let my consciousness think about those things for a bit to remind myself... I do want to support the people of China, I just don't want to be funding any labor camps (see my human rights related posts on the top right of my blog). How much can an individual contribute... even if it is only a thought, at least you thought about it.

In a lot of cases, even if you go for the more expensive stuff, it still turns out it comes out of China or another Asian country. I guess the only way you can be sure is if it says made in the good old USA.

Well, I hope this is an interesting post for the hobbyists and food for though for everyone else. Take it easy :)

The Return of the Boards (part 2)

A quick post tonight to let you know that the PCB boards for the second prototype series are back. It looks like the PCB house did a nice job on them and delivered them with a nice gold finish.

Having a real board in hand makes me realize how small this design actually is. Your perception gets a kind of distorted when you design on a computer screen for too long and are zoomed-in all the time.

Everything is very tightly spaced as you can imagine. The 0.5mm pitch dock connector footprint in the photo is a clear example of this. This board will require some special tools for soldering as a regular soldering iron is unsuitable for some of the parts that go on the board. I had already ordered that equipment earlier this week and it has just arrived as well, waiting to be unpacked...

Saturday, May 3, 2008


I received some new LEDs this week and I soldered another module together with a new high intensity blue/red bi-color LED. I decided to put about 5mA through each of them, not knowing how bright they would be. After assembly, I measured the currents: 3.8mA through the blue LED and 5.0mA through the red LED for a total of 8.8mA... and still sooo much light. That means I can design for an ever lower current and probably cut about another 4-5mA out of the power budget. :)

The picture shows all three modules I have built so far (I had to turn down the sensitivity in order not to blind the camera with the LEDs):

  • On the left, module #1:
    Green/orange bi-color LED (orange shows, but green and orange LED are on simultaneously, orange overwhelming the green)
  • On the right, module #2:
    Blue LED
  • In the center, module #3:
    Blue/red bi-color LED (purple shows, blue and red simultaneously about the same intensity)

Sadly enough, my multi-meter pin shorted to Vcc when measuring the red LED, so it died :( I have some de-soldering to do tonight and fix it.

I also changed the charge resistor for the on-board battery to a lower value so as to recharge that battery a little faster (without exceeding the maximum charge current of course).

Module #3 is also using a slightly smaller patch antenna (see the center module in the photo) of about 13x13x4mm compared to the 15x15x4mm ones that I used for the other modules. I took the module out to the store while on my way buying a digital calipers for the housing design. The module performed above expectation, which is a good foresight for the next PCB board which will be using a chip antenna. It would be great if I can freeze the next design, as the form factor is very small and it has a full dock connector on it. If it doesn't perform well, I have to go back to a patch antenna and a micro-USB port in order to keep the module as small as possible.

Also this week I have made some more new contacts with local contract manufacturers, both for the PCB and the plastic housing. My main next priority is coming up with a final drawing for the housing design so that I can have prototypes made of it.