[Ovmsdev] Cannot reset simcom stuck in PoweringOn state without removing module power

Michael Balzer dexter at expeedo.de
Mon Nov 18 05:29:31 HKT 2019


Am 17.11.19 um 19:31 schrieb Craig Leres:
> On 2019-11-17 04:11, Michael Balzer wrote:
>> I also saw this & can also reproduce this on my workbench.
> What is the method to induce the problem?

No method. If the theory is right it depends on a combination of random circumstances if the MDM_EN signal is long enough for the modem to recognize.

I've got a module from the very first batch (3.0) and a 3.1 development module on my bench. The 3.0 module can power on/off the modem from port 0, the 3.1
cannot. It may also be related to some other condition, as I think the 3.1 module was able to control modem power at least once.

>> Maybe a fix for existing boards could be adding a pullup resistor at the transistor base?
> I could try this if you suggest a value (and perhaps mark up a schematic?)

I think something in the range 130-150K should work. That should put the base to ~0.5-0.6V for low and to ~1.0-1.2V for high. That's either not fully switched
off on low or not fully saturated on high, but should be sufficient for the modem.


PCB (down side):


Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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