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Forgot: you can check if the pullup is working by monitoring the
voltage level on the SIMCOM PWRKEY pin, that's pin 3. When MDM_EN is
high the transistor should draw that to GND.<br>
<br>
Pin 3 is the third from the top on the left side (SIMCOM label
wise).<br>
<br>
The driver puts MDM_EN to high for a whole second, so that should be
clearly visible. Without the pullup, you should only see a very
short pulse, if at all.<br>
<br>
Regards,<br>
Michael<br>
<br>
<br>
<div class="moz-cite-prefix">Am 17.11.19 um 22:29 schrieb Michael
Balzer:<br>
</div>
<blockquote type="cite"
cite="mid:85c51056-4b62-c4ad-82af-bbe1d28a740e@expeedo.de">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
Craig,<br>
<br>
<div class="moz-cite-prefix">Am 17.11.19 um 19:31 schrieb Craig
Leres:<br>
</div>
<blockquote type="cite"
cite="mid:5272bd5b-127a-fe67-333e-4eeb7f9dda88@xse.com">On
2019-11-17 04:11, Michael Balzer wrote: <br>
<blockquote type="cite">I also saw this & can also reproduce
this on my workbench. <br>
</blockquote>
What is the method to induce the problem? <br>
</blockquote>
<br>
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.<br>
<br>
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.<br>
<br>
<blockquote type="cite"
cite="mid:5272bd5b-127a-fe67-333e-4eeb7f9dda88@xse.com">
<blockquote type="cite">Maybe a fix for existing boards could be
adding a pullup resistor at the transistor base? <br>
</blockquote>
I could try this if you suggest a value (and perhaps mark up a
schematic?) <br>
</blockquote>
<br>
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.<br>
<br>
Schematic:<br>
<img src="cid:part1.BAB0BEFA.4528BAB7@expeedo.de" alt="" class=""><br>
PCB (down side):<br>
<img src="cid:part2.E777C93D.E83D7A58@expeedo.de" alt="" class=""><br>
<br>
<br>
Regards,<br>
Michael<br>
<br>
<pre class="moz-signature" cols="160">--
Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
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<pre class="moz-signature" cols="160">--
Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
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