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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.


Bobby said...

Just to make sure that I understand this is for the other side of the board that is not connected to the iphone? would it be stable enough to have the actual ipod connector is someone hooked it up to their doc? or would it crack and fall over?

I think that if you use the mini (most cameras use this) that it will be great.

Chris Chan said...

I think the next step would be more concern on the software than what kind of the connector would be use.

As long as we can charge up the iphone , and the cable for doing so can be provided by you , then everything would be ok.

Anyone have experences on iphone development can feel free to contact me. moming2k at

hdd123 said...

As bobby says, Mini is certainly common place and as such many have already got suitable cables to connect/charge - thus this would help to keep the cost of adopting the plug-in down as there would be no new cables to purchase. Following this train of thought, an alternative suggestion would be the Enhanced version which would give more pinout options.

All this said, you are the architect for this project and I would have to agree that Micro is best for a charge/data option.

Not wanting to be a bore but would it be possible to also incorporate a mini jack socket for audio out as it would be great if it was available through the plug-in. This would enable the iPhone to be easily cradled in the car without the need for cables coming out of both ends! As per conversation elsewhere, I appreciate that enabling audio out through the dock connector is more than just plugging in a set of speakers. Does the iPod pin-out information give any clues for a particular resistance that indicates a docked iPhone with external speakers attached?

J D said...

I don't care at all, I just want the thing to come out already so I can give you my money ;)

:o( said...

When can I have one? WHEN?!!! I'm waiting for to long. One off these days some guy in China takes the idea and starts selling on ebay.


J D said...

Just relax. He's trying to come up with the best design he can here. That takes work, and work takes time.

I have every confidence that these devices will be ready to go in June or July; he's making great progress.

Man, now I'm going to be buying TWO homebrew serial devices for my iPhone: this and the iControlPad :) Too bad Apple didn't take advantage of this potential market themselves. Their loss.

Josh said...

Great project! I look forward to ordering one! Have you done any analysis on how much current the 3.3V output pin will supply? Obviously it is enough to power your ~65 mA GPS, but have you looked at currents above this?

David Brown said...

Please place a donate option so that the iPhone community can support you on your hard work.

chris chan said...

there is another gps project for iphone called "xGPS - GPS for iPhone / iPod touch", seems to be more and more people join the development , and looking forward for more application

Tom said...

I think the software of the xGPS project will be compatible with this module. At least, this is what they say on their site: "his project goal is to develop an open GPS hardware and software solution for the iPod touch and the iPhone."

Since the module being developed here uses the standard output, I think it should work with that software.

Someone else asked if it would be possible to add an audio output. I would like to second that question. This would make it handy to hear instructions from the GPS software. Is there any room on the design of this module?

J D said...

I think that sort of thing is best left on the application end. After all, the iPt and iPhone both have their own audio hardware that could be bent to that purpose.

GPS said...

To address a few of the questions:

bobby: there is currently no space for a full ipod connector as we would like to keep the module as small as possible. Also, although it would be nice to have one, there is not really a need for more than a USB connection for charging and syncing. Sound is available from the headphone connector on both the iPhone and iTouch.

hdd123: I haven't been able to find a way to enable the sound from the dock connector without having the "this accessory is not made for iphone" box pop-up. I guess it comes down to taking apart the iPhone dock and seeing what is in there.

j d: I am working as fast as I can with the limited time I have. If I could support my family from doing this, I will get on this project (and many more to come) full-time. I am seriously debating it as I have acquired all the needed skills while working my regular full-time job. Maybe there are more gadgets that you wish to have for your iPhone/iTouch. Feel free to share them.

:o(: Yeah, one can always reverse engineer things. I see it like this: I am developing this with feedback from you guys, I am putting 100% effort in this from my side (I am striving to be a perfectionist), so hopefully in return by providing the best, the customers will stay loyal.

josh: I haven't looked at how much current the dock can handle. There is probably a way to find out without frying the phone. I would guess, maybe a couple of hundred mA max. Also, you wouldn't want to be drawing too much current to save battery life.

david: a donate button, yes, I will look into this. It might provide me with useful feedback if I should go into this full-time.

tom: yes, the module will be compatible with any program that uses standard NMEA commands or that uses a gps daemon. Regarding the audio output, see my comment above. In principle all this could be added, making a bigger package, but it is not really needed. You can use the headphone jack and have volume control as well.

J D said...

Oh, man. gpsd support would be FANTASTIC. The possibilities are endless.

I just want to thank you again for all your hard work. We're all pulling for ya :)

I don't know that there are other gadgets I'd want... but fixed Bluetooth would be great. That gets into a whole other universe of development, though -- I don't know that anyone has been able to get kernel modules working under iPhone firmware.

Anonymous said...

Where can you buy the 30-pin iPod-dock connector?