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Monday, April 14, 2008

Quietly steaming along.....

Things have been busy last week. I have built the second GPS module. There were a few hick-ups along the way which slowed things down a bit. Quality control on parts is a MUST. I had a few parts that weren't up to spec. It took me three evenings to figure this out and fix the problems. I wish there was more free time in a day.

The second module (the right phone in the photo) uses a slightly different GPS module. This module consumes less power:

  • Module #1 (on the left):
    • Consumes about 65mA at 3.3V on startup (that is when searching for satellites)
    • Consumes about 50mA at 3.3V when tracking (GPS lock)
    • Green LED is continuously on all the time. A high brightness orange LED in the same package starts flashing when a GPS lock is achieved.
  • Module #2 (on the right):
    • Consumes about 55mA at 3.3V on startup (that is when searching for satellites)
    • Consumes about 35mA at 3.3V when tracking (GPS lock)
    • Blue LED is on continuously when searching for satellites and changes to flashing when a GPS lock is achieved.
Talking about power consumption, the technical specifications for the iPhone battery can be found at Apple's website.... well so much for technical specs on that link. Actually on that page there are no technical specs for the battery, only that battery life depends on usage.....

Searching around the internet, one can find that the battery in the iPhone has a capacity of 1400mAh and a voltage of 3.7V. So plugging in my GPS module for one hour, will add approximately an additional 35mA of current load to the phone (about 2.5% of the battery capacity). To speak in laymen's terms, not too much to worry about. I have been playing around with module #1 over the last couple of weeks, having it on continuously during my drive from and to work (about an hour each way) and I still get about 2 days of battery life out of the phone. To be honest, I think it is more determined by how much Wi-Fi I use during the day than anything else.

But, since the question has come up quite a few times already, for those who are worried, there is a mini-USB plug on the module which allows you to charge and sync the phone as needed.

And then on a final note, I have also included a lithium rechargeable battery on the PCB board now that will keep the acquired satellite positions saved in the GPS module (see the photo above; click on it for a larger view). In that way, you will get a fast GPS lock (within about 5-10sec) after your first initial lock (which can generally take up to a few minutes depending on where you are). This lithium battery is charged from the phone with a current of about 0.05mA and will last about 8 days without recharging by the phone.


Alex said...

Sweet. Thanks for keeping us updated.

Tom said...

Hey, I've been following this a bit now, and find this very interesting.
But what are your future plans? Releasing the schematics for the hardware so we can get soldering? Releasing/selling your GPS software/hardware?

A lot of people would be interested in this, I'm sure. So I'm wondering where this is heading to :)

Mike said...

Hi! I've been looking at GPS for my iPhone for a little while now. I now understand how to assemble GPS, 20-pin, and USB but not a battery (and I don't have very much experience soldering). I'd like to learn now that someone is offering up free/open software. Would you care to shoot me some pointers? ..maybe a test module? :-D

Mike said...

Hi, the project looks interesting! I am also investigating into a possible solution to get a GPS working on the iPhone and I would like to ask you a few questions. Can I get your email? my email address is


J D said...

You are my freaking hero, man. I promise I will be one of your first customers!

GPS said...

To answer the few questions:

The future plans are to make the hardware module available for sale as soon as the prototyping/testing is finished, the package designed and a first production run of 1000pcs can be run.

Regarding software, Simba has already made some free software available with basic functionality that runs with the module. Morten is porting RoadMap to the iPhone and has already shown a basic first proof of principle.

Anonymous said...



Lutz said...

Wish you all the best with that project. One small usability comment if I may. THe LED should flash while searching for satellites and stay on permanently when it has a lock (steady=good, blinking=bad). You could use half phases or such to reduce the power consumption. Don't make it into a torch please.

Darren said...

Good point on the LEDs, way to annoying to have it flash when sat lock is achieved and contra to how people expect them to operate.

Flash when searching, steady when sat locked and I second the call for the LEDs not to be so bright they are distracting/annoying!

GPS said...

Thanks for the feedback regarding the LED. I will check if something can be done about it; this function is fixed into the GPS chip, but maybe it can be re-programmed.


Chuan Kang Shih said...

I think this is brilliant!
I would be more than interested in purchasing in bulk and doing reselling (or maybe doing a reselling agreement with you in Australia/New Zealand?) once you have this set up!
I will be keeping an eye on this with a lot of interest!

Anonymous said...

hey so you have this for sale yet???

Anonymous said...

hey so you have this for sale yet???