In the FONA faq it is said that one can run FONA without USB power & a battery. This does not seem to be correct. I used a LM317T to create a 3.9V power source and connected this to VBAT (or rather BAT since the "V" seems to be cut off the PCB?). This was powered by a 5V / 2A switching power supply and the LM317T should be able to supply in excess of 1.5A for short periods.
I also soldered in a 220uF cap between GND and BAT to help with the described spikes in power usage. I'm running this with a Teensy 3.1 and it works perfectly when running off a battery. When I'm powering it directly it fails as I try to register on the network.
The module powers up and fully works. When I try to unlock the SIM and register on the network, the FONATEST sketch returns:
Code: Select all
Unlocking SIM card: OK!
Code: Select all
Network status 0: Not registered
Code: Select all
Enter 4-digit PIN
1234
Unlocking SIM card: Failed
OKFONA>
Anyway - I get the exactly same behavior if I unplug the battery and power the module only from USB. It REALLY seems to be that one cannot run FONA without a bettery attached that can solve the (apparently massive) power spikes when registering on a network. This should be noted in the FAQ so that others don't need to spend the hours I spent on this.
(Long rambling coming to an end now)
I have a final question regarding powering my projects. The (V)BAT pin will deliver about 4V when connected to either a battery or USB. Are there any reason why I should NOT use this to power the Teensy? Thanks!