Hi all,
It has been mentioned at several places in this forum that MKRGSM1400 needs a 3.7 V lipo battery connected to establish gsm connection. That is because the USB power supply, or a solar power supply cannot provide enough current during the initial negotiation phase between the board and the cellular tower.
According to different messages, the battery should have a capacity > 1500 mAh.
If there is no battery connected, the board will freeze during the GSM connexion, and here is what I can see : If you instantiate the gsm object with the TRUE option, the debug console will show all AT commands
GSM gsmAccess(true);
When you call : gsmAccess.begin(PINNUMBER)
, at some point the SARA modem will receive several AT+CREG? command, until it picks a signal.
Without battery , or a defective batery, or a battery that cannot furnish enough current, this AT+CREG? loop just freeze, and the board is completely frozen.
If you want to use a MKRGSM1400 with a solar panel, in a remote location, and you require periodic reconnexion to GSM network, you are at risk that the battery is too low at the time of the GSM reconnexion In that case, you lose control of the board.
Yes you could check the battery voltage before reconnecting but I have noticed that this is not a correct indicator. Even a battery like 18650 1S3P 7800mlAh showing more than 4V can sometimes be too weak !
so my question is :
Can this issue be adressed programmatically, by modifying the mkrgsm library ? for example adding time outs in the AT+CREG? loop? so that the whole board does not freeze in case of not enough current being furnished by the battery ?
Or is this a hardware limitation of the board and especially the SARA modem ? In that case, I would say that the mkrgsm1400 board is useless for a remote autonomous project.