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. Pin 3 is the third from the top on the left side (SIMCOM label wise). 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. Regards, Michael Am 17.11.19 um 22:29 schrieb Michael Balzer:
Craig,
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.
Schematic:
PCB (down side):
Regards, Michael
-- Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
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-- Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
