SparkFun Forums

[mcguire]

Hello, fellow SFE fans. I received a GM862 a few days ago and am trying to get it working. I've been working with this type of circuitry for many years and am comfortable with it; I'm pretty sure I've set it up correctly...but I see no signs of life from the GM862. I'm wondering if anyone can provide any advice. I will describe my setup.

On a solderless breadboard, I have a brand new GM862 installed on the SFE bare-bones carrier board, with one metal tab soldered for a solid ground. I'm powering it from an LT1528 regulator set for 3.8V using a 1K trimmer resistor, with two paralleled 47uF/10V tantalum capacitors and one 0.1uF ceramic capacitor on the output, and one 47uF/10V tantalum capacitor on the input. Also on the breadboard is an LM2937-3.3 powering a MAX3232 level converter. The whole breadboard is powered by an adjustable switching bench supply set for 5V. That supply tops out at about 5A. I also have an LED connected (with the correct polarity) between the GM862's "status LED" output to a 330ohm resistor, then to +3.8V. I have a pushbutton switch wired to the GM862's "power on/off" pin. An MMCX->SMA pigtail and a quad-band antenna complete the setup.

When I apply power and exercise the power on/off pushbutton switch, I get no activity on the serial port, and no activity on the LED. I have swapped LEDs, series resistors, and MAX3232 chips, I have verified all supply voltages with a good meter, and checked the power supply (both before and after the regulators) for noise with an oscilloscope and have found nothing above ~10mV. When I look at the serial lines with the scope, I see the data coming from my computer when I type "AT<cr>", but nothing coming back. All of the behaviors noted above are unchanged with the addition of a SIM card.

I have inspected the connector on the SFE carrier board under a microscope and it is fine. I have also tried different areas of my solderless breadboard (in case I have worn pins), to no avail. I know the module is getting power; several lines (CTS for example) are low when I apply power to the board, but go high when I pulse the "power on/off" line. It just seems like the module is not fullly initializing for some reason. I've pulled the "reset" line low and that doesn't seem to do anything either.

Does it need to see any other signals to come up and respond to "AT" commands? What am I missing here?

(I apologize for the verbosity of my post; I'm trying to give a complete description of what I'm seeing)

Thanks,
-Dave McGuire

[jasonharper]

How long are you holding down the power button? I believe the GM862 requires a second or two to recognize it.

[mcguire]

While digging through the forums yesterday, I noticed that someone else had mentioned that, and tried it...no change. I've tried holding it down for quite a while, maybe 7-10 seconds or so. No joy.

-Dave

[busonerd]

Hmm, so the status LED does not flash? Means you're correct that the module is not initializing.

I assume you have it all wired up similar to our RS232 EVK schematic right?

Cheers,

--David Carne

[gm]

How about the RTS line. The Telit Hardware guide suggests tying it to ground (on the module side) if flow control is not used. Don't leave it floating.

Hope this helps,

Greg

[mcguire]

David, I've checked the RS232 EVK schematic as you suggested...no material differences...I'm using 2x 47uF capacitors on the output side of the 3.8V regulator instead of one 100uF, which of course won't make any difference. I've verified with a scope that the power is clean, at any rate.

Greg...I tried grounding RTS, no difference. There has to be something else that I'm missing here. The only other possibility I can come up with is a DOA module, but that seems very unlikely.

-Dave

[mcguire]

Well I am close to giving up on (this) GM862 module...I think it is DOA. I have spent many hours poring over the datasheets, as well as archived posts from mailing lists and forums (including this one...there's some great stuff here!) but have still gotten nowhere.

Has anyone else had trouble with a DOA GM862? What are SFE's policies regarding stuff like this? Ordinarily I'd not worry about it and order another one, but this is a $150 module!

-Dave