Arduino GPRS shield caught fire

LukeZ: Yeah, running power through VIN seems to work though I've only tested the shield by itself on the bench and not with the Arduino in the final application.

For my application having different tensions isn't so easy, so I was thinking about 12V both for Arduino and the GSM shield but in parallel. Sounds good to you? I can manage to have a 5V line for the Arduino itself and a 12V one for the GSM shield, but only if not possible in other ways.

Thanks for sharing LukeZ, I really appreciate it.

Yes, 12v to VIN for both should work fine.

Both the 5v (from the Arduino regulator) and the VIN pins are connected to the GSM shield. As best I can read the schematic, if the GSM shield detects 5v on the 5v pin, it will try to use that instead of VIN, and this is when the capacitor comes into play. If you cut (or bend out of the way) the 5V pin from the Arduino to the shield, then the shield will be forced to use VIN. At that point we have exactly what you propose: 12v to both devices in parallel, and each device will use its own on-board regulator.

I'm not the expert on this stuff so I hope others will confirm but this seems correct to me.

I agree with you Alek, Arduino really needs to put a note about this issue on the wiki page.

LukeZ: Yes, 12v to VIN for both should work fine.

Both the 5v (from the Arduino regulator) and the VIN pins are connected to the GSM shield. As best I can read the schematic, if the GSM shield detects 5v on the 5v pin, it will try to use that instead of VIN, and this is when the capacitor comes into play. If you cut (or bend out of the way) the 5V pin from the Arduino to the shield, then the shield will be forced to use VIN. At that point we have exactly what you propose: 12v to both devices in parallel, and each device will use its own on-board regulator.

I'm not the expert on this stuff so I hope others will confirm but this seems correct to me.

I agree with you Alek, Arduino really needs to put a note about this issue on the wiki page.

as far as I can see, I think that it is the contrary : if VIN is there ( and > 5V) , it is used instead of 5V : edit : here is how I understand it (short version ;) ) If Vin is applied (and > 5,7 V) : - Q5 is ON, which makes T1 Gate high -> T1 is off (which makes sure that no current will flow back in +5V supply from PWRIN which is at a higher voltage) . - Q5 ON makes Q6 ON, which puts T2 Gate à 0V -> T2 is ON -> PWRIN is at VIN voltage -> LMZ12002TZ 's VIN is at VIN voltage

You may be right, and hopefully so. As I mentioned before, I really can't make out what is going on with the power input transistors and mosfets leading into the shield's regulator.

Cutting/removing the 5V pin to the shield may then be unnecessary, but wouldn't hurt.

LukeZ: You may be right, and hopefully so. As I mentioned before, I really can't make out what is going on with the power input transistors and mosfets leading into the shield's regulator.

Cutting/removing the 5V pin to the shield may then be unnecessary, but wouldn't hurt.

sorry, while you were writing, I modified my post to add the way I understand the schematic

As there are no recent posts on this interesting theme, I have to say that the GSM shield recently bought, has a zener diode soldered in parallel to the problematic capacitor. So, I think this kinda solve the problem.

Would love to see a pic from this new board. Any Specs to the diode?

Best regards

Hi,

sorry for this late response. Here https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRsx7i6S0QzynAEEK6EIvl_opmtTw4mfAHcTQHte_XGUloDbfUdVQ you could find a photo of this zener diode soldered in parallel of the tantalum cap. Tonight, when I get back home, I will check again what was the exact number of the diode and will post here it's data sheet.

Regards,

Erik

Hi again!

I am looking now at my GSM shield. Just to make clear something, this is not a new board, I mean generally. There is just this zener diode added to overcome this design flaw. Here http://www.futurlec.com/Diodes/1N5338B.shtml, you can check its characteristics. The diode is 1N5338b.

Regards,

Erik

Ahh, this info helps a lot. Would you mind to take a pic from your shield? The pic you posted is so small.

Best regards toonlumberjack

Sure,

an image is attached. :slight_smile:

Regards,

Erik