0

FONA without battery
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

FONA without battery

by jensa on Mon Jan 05, 2015 7:13 pm

Hi,
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 | TOGGLE FULL SIZE
Unlocking SIM card: OK!

This looks good, but it will only try to register for a very short time and it will always fail. Network status will then return:
Code: Select all | TOGGLE FULL SIZE
Network status 0: Not registered

If you try to register on the network again, you'll get this output:
Code: Select all | TOGGLE FULL SIZE
Enter 4-digit PIN
1234
Unlocking SIM card: Failed
OKFONA>

Note the final output "OKFONA". This seems to indicate that something has the wrong state in the FONA library?

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!

jensa
 
Posts: 159
Joined: Wed Dec 21, 2011 9:35 pm

Re: FONA without battery

by adafruit_support_rick on Fri Jan 09, 2015 11:37 am

Some customers have reported successfully powering in the FONA from VBAT. Not sure why you're having trouble.

You can use VBat as an output to power the Teensy.

adafruit_support_rick
 
Posts: 34332
Joined: Tue Mar 15, 2011 11:42 am
Location: Buffalo, NY

Re: FONA without battery

by jensa on Fri Jan 09, 2015 1:56 pm

I ended up using a battery (since there were no way to not do so) and to power the Fona and Teensy from separate USB power sources. When the Fona registered on the network, it produced so much noise that it crashed the SGTL5000 chip on the Teensy Audio Adaptor sitting next to it on the PCB. By itself, everything would work fine. As soon as the Fona tried to register on the network, the SGTL5000 would produce nothing but random and loud noise. Only way to remove the noise was to remove power from the Audio Adaptor and thus the Teensy.

It works fine as long as I mount the two about 20cm away from each other. Makes the setup less nimble, but it works perfectly fine.

jensa
 
Posts: 159
Joined: Wed Dec 21, 2011 9:35 pm

Re: FONA without battery

by customdev on Tue Feb 10, 2015 7:36 pm

I got mine to work fine with a single 5V supply with no noise issues using the recommended regulator on the SIM800 datasheet, if interested, let me know.
customdev
 
Posts: 19
Joined: Fri Feb 25, 2011 12:06 pm

Re: FONA without battery

by jensa on Wed Feb 11, 2015 4:23 am

@customdev Did you use the Teensy Audio board too? How was it mounted in relation to the FONA?

J

jensa
 
Posts: 159
Joined: Wed Dec 21, 2011 9:35 pm

Re: FONA without battery

by stoutfiles on Sat Mar 07, 2015 12:13 am

customdev wrote:I got mine to work fine with a single 5V supply with no noise issues using the recommended regulator on the SIM800 datasheet, if interested, let me know.


Please share, I'd love to know how you did it.

stoutfiles
 
Posts: 27
Joined: Fri Mar 06, 2015 11:58 pm

Please be positive and constructive with your questions and comments.