I’ve been playing around with the GM862 USB v3 eval board. I’ve been successful in using the GPS part of the GM862 from the USB port of my PowerBook, but I’ve run into some problems.
However, in order to start the GSM service up, it needs more power than the USB port alone can supply - fine. I needed to find a 5V DC supply that can handle a peak of 2A.
I chose a 5VDC 2.5A regulated plug pack and then had the choice of polarity on the DC plug. The PDF on the web site was for the V2, and there was no indication on the circuit board which one needed to be +ve.
A crackle, flash and pop indicated I had made the wrong choice. I rapidly unpluged the power pack, but it had smoked a SM component - I am guessing it is a diode, but it is beyond identification now. I removed the charred remains and confirmed the board still works with the USB port.
Can someone help me identify this component? In the attached photo, it is the larger one near the ft232rl usb controller.
Also, if anyone has any (general) advice for powering the V3 of this board, I’d love to hear from you. The PDFs online are hopelessly outdated. Ideally I’d like to run this off a 12V DC car circuit, but also incorporate a battery to provide power if the car battery is disconnected.
Looking at the schematic it appears to be a 10uf tantalum capacitor (C7), and they will explode if the polarity is reversed. It looks like the power plug should have the inside of the plug positive and the outside of the plug should be ground.
I have got the similar GE863-GPS working OK at 3.7V with a bench supply that gives 1.5A maximum. I have a 100uF tantalum capacitor at the supply input to the GE863, as recommended in the hardware manual.
A good quality bench supply is the best thing to use when working with this sort of equipment, they aren’t expensive. I use a Lascar PSU 130 which cost about £60.
Thanks to a follow-up email to tech support, it is a 10uF tat cap.
I chose a 16V one and solder it relatively easily. The +ve is to the right (as oriented from the photo in the original post)
I’ve had success with a 1.5A plug pack delivering 5V, even though it is a bit underpowered. Yes - the centre pin is +ve.
For 12VDC power from a the car, I used a LM317T with a heat sink, and a simple step-down to 5V. The heat sink gets a little warm, but it’s not too bad. If anyone wants more details, I’ll post them here.
While we’re talking about power and the USB EVK v3 - I’m interested in hooking a Li-Ion battery up to mine so that it is self-powered but USB charged (and comms probably still go through USB).
This means that I nead to connect the 3.7V Li-ion cell across 3.8V and ground; however I have to either force the LT1528 into shutdown using its shutdown pin or physically cut the output lead away from the board (which would mean that the 3.8V battery supply would still power the 2.8V regulator for the FTDI logic voltage.
The 5V USB power I can then hook to the “charge” pin brought out on the edge of the board.
I haven’t started this yet and I suspect I am missing something… has anyone done this before with one of these boards?
