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.
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.