Hello, I have the wp76xx variant of the mangoh yellow. I have been reading forums etc trying to find out how I can trigger the module to wakeup after a power outage automatically. I have tried using AT commands to modify the voltage limits.
By default my module LO_NORM is 3700. If i run the AT command
Volt state: Normal
Power supply voltage: 3671 mV (ADC: 37148)
I see that the power supplied by my USB port is usually slightly under 3700 by a few tens of mV. I’m running the test in 2 methods:
I’m simply unplugging the usb1 connector (no battery connected), waiting a while, and then plugging it back in. I leave the switch in the ON state the entire time and after i plug the USB in, the module never boots up. I have to physically press reset.
I have a 16port USB hub that has switches that I can physically disable the power port by port. Disabling the power and then re-enabling the power also doesn’t trigger the module to turn on.
Is there something special that I need to do to trigger the module to turn on after a power outage?
On the mangoh yellow board, there is a capacitor C410 that unless this is discharged, will not trigger the POWER_ON_N signal long enough (through U407) to actually trigger the boot from my observations. I don’t have an oscilloscope unfortunately to tell you how long the POWER_ON pin is getting triggered, but the green power LED flashes just momentarily and then nothing.
Shorting the capacitor to discharge it is fine, but I was looking for a way to get around this issue without physically touching the modem or re-design the power-up circuitry of the mangoh yellow. But it looks like only solution is to redesign this circuitry from the mangoh default.