Cellular + GPS tracking, all in one, for your Arduino? Oh yes! Introducing Adafruit FONA 808 GSM + GPS Shield, an all-in-one cellular phone module with that lets you add location-tracking, voice, text, SMS and data to your project, in Arduino shield format for easy use.

This shield fits right over your Arduino or compatible. At the heart is a powerful GSM cellular module (we use the latest SIM808) with integrated GPS. This module can do just about everything

  • Quad-band 850/900/1800/1900MHz - connect onto any global GSM network with any 2G SIM (in the USA, T-Mobile is suggested)
  • Fully-integrated GPS (MT3336 chipset with -165 dBm tracking sensitivity) that can be controlled and query over the same serial port
  • Make and receive voice calls using a headset or an external 32Ω speaker + electret microphone
  • Send and receive SMS messages
  • Send and receive GPRS data (TCP/IP, HTTP, etc.)
  • PWM/Buzzer vibrational motor control
  • AT command interface with "auto baud" detection

Here's the GPS specifications:

  • 22 tracking /66 acquisition channels
  • GPS L1 C/A code
  • Sensitivity
    Tracking: -165 dBm
    Cold starts : -147 dBm
  • Time-To-First-Fix
    Cold starts: 30s (typ.)
    Hot starts: 1s (typ.)
    Warm starts: 28s (typ.)
  • Accuracy: approx 2.5 meters

Sounds delicious, right? So we plated this fine module onto a shield with all the extras you need to make your next project shine

On its own, this shield can't do anything. It requires a microcontroller like an Arduino to drive it!  You will also need some required accessories to make FONA work. These are not included!

Each order comes with one tested and assembled FONA shield and a stick of 0.1" male header. Required Arduino, SIM card, battery, antenna and other accessories are not included! Some light soldering is required to put the headers onto the shield. You can also grab some stacking headers if you would like to stack a shield on top

There's also some recommended accessories. They are not required but chances are you'll want them!

There's a lot going on in this shield, we basically stuffed an entire phone in here! So lets go piece by piece on what you get in a shield


There's three external connectors along the left side, from the top, a headphone jack, a uFL connector and a 2 pin JST-PH. There's also a second uFL connector in the top middle.

  • Headset jack - this is a 'standard' TRRS 3.5mm phone headset jack with stereo earphone and mono microphone. Any 'iPhone' or 'Android' compatible (but not iPhone original) should work. We tried about 10 different ones, and basically the more expensive once are more comfortable and louder but our official iPhone headset mic did not work for unknown reasons. Sleeve is Mic+, first ring is ground, then the second ring and tip are for stereo audio. The module does not have stereo out so we just tied both together.
  • uFL RF connector - This is the Antenna connector, an antenna is required to use the FONA shield! You can either use a uFL GSM antenna like this, or use a uFL to SMA adapter and then an SMA antenna
  • JST 2-pin - this is the battery input connector. It works with any of our Lipoly batteries but since the charge rate is 500mA (and the cellular module can spike high current draw!) we suggest our 500mAh or 1200mAh batteries. You can also connect a JST cable here if you have other plans.
  • uFL GPS connector - this is the GPS Antenna connector, an antenna is required if you want to get GPS readings! You can use this 15mm passive antenna, or any other passive 50 ohm antenna with a uFL connector. You cannot use an active antenna, although we have added some spots for optional bias circuitry, we couldn't get it to work with our active antennas so we left the pads there but not assembled.

Charging Circuitry

A lipoly battery is required to run the FONA shield, as there's up to 2A mini-spikes during cellular connectivity. To make it easy to keep the battery charged, there's charging circuitry onboard. The battery is kept topped-up by the 5V Arduino pin. We charge at a 200mA rate. You can check the status by looking at the CHRG and DONE LEDs.  Charging occurs whenever the switch is set to CHRG

You can also run the Arduino + Shield off the battery. It will run at a lower-than-5V level, around 3.7V or so. It's a under the common 5V voltage so if you are reading analog voltages and expecting 5V note that those numbers will be off, but for digital usages, it tends to be just fine. To run the Arduino+Shield off of LiPoly, set the switch to RUN

SIM Connector

A 2G Mini SIM card is required to use the module. Nearly any cell phone shop can sell you a SIM card. It must be a 2G GSM card. AT&T in the US does not sell these anymore! They are shutting down their GSM network, and only T-mobile sells and supports a GSM network. If you are in another country, chances are you can just ask for a GSM 2G card. For USA customers, we have a known-working TING SIM card which has a great billing system and works very well!

MicroSIMs won't fit - so make sure its a "Mini" SIM. Mini SIMs are 1" x 0.6" / 25mm x 15mm. These are by far the most common size.

Most cards come with a voice and/or data plan. If you want to make phone calls and SMS's you'll need a voice plan. If you want to transmit data like fetching a webpage, you'll need a data plan.


  • PWR - green! Lit when the Cell module is booted and running
  • NET - blue! You can use this for checking the current state without sending an AT command:
    64ms on, 800ms off - the module is running but hasn't made connection to the cellular network yet
    64ms on, 3 seconds off - the module has made contact with the cellular network and can send/receive voice and SMS
    64ms on, 300ms off - the GPRS data connection you requested is active
    By watching the blinks you can get a visual feedback on whats going on.
  • Charging - Orange! This is next to the JST jack. Indicates the onboard lipo charger is charging
  • Done - Green! This is next to the JST jack. Indicates that the battery charging is done and the battery is full

Shield I/O Breakouts

The most important pins are broken near the top left of the board. This is how the Arduino will communicate with the FONA shield!

These pins are all 3-5V input safe and if they are an output, the logic level is whatever VCCIO is set to (see the VCCIO jumper near the FONA logo, by default we use 5V logic, for 3.3V logic-only Arduinos, cut the trace and solder the middle pad over to 3V

Starting from the right

  • RX & TX - The module uses UART to send and receive commands and data. These pins are auto-baud so whatever baud rate you send "AT" after reset or boot is the baud rate is used. RX is into the module connected by default to Digital #2, TX is out of the module, connected to Digital #3. The default connections will work on a Uno, but other arduinos may not support software serial on pins 2 and 3.  Check this page to see what pins to use on your arduino.
  • Reset (RST)- this is module hard reset pin. By default it has a high pull-up (module not in reset). If you absolutely got the module in a bad space, toggle this pin low for 100ms to perform a hard reset. We tie this to Digital #4, and the library does a hard-reset so you always have a fresh setup.
  • RTS (Ready To Send) - This is the module's flow control pin, you can use this to control how fast data is sent out from the module to the Arduino, good when you want to read only a few bytes at a time.
  • RI - this is the Ring Indicator. It is basically the 'interrupt' out pin from the module. It is by default high and will pulse low for 120ms when a call is received. It can also be configured to pulse when an SMS is received. This is not connected to any pin by default, so solder a wire if you want to use it!
  • Net - this is the Network status pin. It pulses to signal the current status of the module. This is also tied to the Net LED so for more detail see the LEDs section
  • Pwr - this is the Power Status pin. It is low when the module is off and high when the module has power. If you're using the Key button or pin, you can monitor this pad to see when the module's booted up. This is tied to the Pwr LED too.
  • Key - This is the power on/off control for the module. Its also tied to the button in the top left. When this pin is tied to ground for 2 seconds, it turns the module on or off. It's not a level signal so it isn't like "low is off, high is on" - instead you must pulse it for 2 seconds to turn off/on. The module comes by default on (tied to GND) so the module will come up immediately. If by chance you want to control this pin, cut the GND-jumper right below this pad and use with any microcontroller output pin

Audio Breakouts

  • SPK+ and - : This is for connecting an external 32 ohm speaker, max 0.2W. This is the same output as the headphone jack, but 'direct drive'. You cannot connect this to a stereo, powered speakers or other non-differential amplifier without adding a 100uF+ blocking cap in series to the + pin and then not using the - pin. Instead, your amp should use GND for the - reference
  • MIC + and -: this is for connecting an external electret microphone, it will bias the mic with 2V. Most electrets will work just fine. No extra circuitry is required for the mic such as a biaser or amplifier, just wire it up directly!

Other Breakout Pins

We scattered a few other breakouts around the board.

  • Buzzer and PWM - These are tied to the PWM output of the module! The PWM capability is quite nice, it can set any frequency and duty cycle. The PWM pin is directly output from the module and is 0-2.8Vpp. The Buzzer output has a NPN drive transistor so it can run a small vibration motor. Bz+ is the VBat voltage, Bz- is toggled on and off to ground.
  • PPS - this it the 'pulse per second' output of the GPS. We didn't have space for a level shifter so this is a 0-2.8V signal, so you may not be able to read it on a 5V logic Arduino. However, if you really need it, you can shift it manually.

In order to use the phone parts of FONA you will need a SIM card. Luckily, there's a phone store in every town in America! You can get a pre-paid or post-paid SIM but we kinda like the pre-paid kind.

A 2G Mini SIM card is required to use the module. Nearly any cell phone shop can sell you a SIM card. It must be a 2G GSM card. AT&T in the US does not sell these anymore! They are shutting down their GSM network, and only T-mobile sells and supports a GSM network. If you are in another country, chances are you can just ask for a GSM 2G card.

MicroSIMs won't fit - so make sure its a "Mini" SIM. Sometimes these are just called plain "SIM" cards since the huge-size SIMs are rarely used. Mini SIMs are 1" x 0.6" / 25mm x 15mm. these are by far the most common size.

The only thing to watch for is you need to have a 2G GSM-compatible SIM

In the US, AT&T no longer sells 2G SIMs! We suggest T-Mobile or T-Mobile "distributors"
If you have an older AT&T SIM it may work. AT&T announced in 2012 that they would shut down their 2G network January 1, 2017. The vast majority of M2M (machine-to-machine) cellular devices use GSM, so the 5 year lead time was to give people plenty of time to migrate from AT&T.

You can read an interesting whitepaper from Aeris about this below:

T-Mobile & TING

T-Mobile does not have any announcement that they will sunset GSM. We can't speak for them but we expect at least 5 years warning as well, probably they will never fully sunset since there's millions of machines with GSM connectivity.

Adafruit now sells the TING SIM card, a 2G GSM SIM that works great with all FONAs, and has a great billing system as well, where you only pay what you use!

If you don't want to use TING, there are dozens of T-Mobile resellers such as Walmart, SIMPLEMOBILE, etc! Just ask the seller if its AT&T or T-Mobile network. If they get cagey just say your apartment has no AT&T coverage.

You do not need to bring in or show your FONA to the Cell Phone store. Just tell them you need a Mini SIM for a GSM phone and it's at home.

Some suggestions from FONA users!

We haven't tried all of these SIMs so you may need to try it out. For other countries, GSM is very common so you should be able to buy a SIM from any cell phone store.

Stack Alert!

If you want to stack a shield on top of the FONA Shield, you'll want to pick up some stacking headers and use those instead of the plain header shown here!  

Wanna stack? This tutorial shows how to use the plain header to connect to an Arduino. If you want to use stacking headers, don't follow these steps!

Attaching Header

Begin by breaking the 36-pin male header into four pieces: one 10-pin, two 8-pin and one 6-pin. Stick the header into the Arduino sockets with the long pins down.

Place the shield on top so that all the little pins stick out through the matching holes in the shield. It should match up perfectly!

(These photos show a FONA 800 shield, but the overall process is identical for the FONA 808)

And Solder!

Be sure to solder all pins for reliable electrical contact.

(For tips on soldering, be sure to check out our Guide to Excellent Soldering).

You're done! Check your solder joints visually and continue onto the next steps

Attaching Antennas & Battery

A battery and GSM antenna is required to use the Cellular module. If you want to use GPS as well, a passive GPS antenna is also required

Check polarity for the battery!
Snap the uFL connector on, it will click when placed properly

SIM Card

You must insert a SIM card to do anything but the most basic tests. The shield and GPS does work without a SIM but of course you cannot send or receive texts, calls, etc!

The SIM card holder it on the right side of the shield. It holds a very-standard "Mini SIM"
Micro SIMs will not work! Make sure you get a "Mini SIM"

Open by sliding the cover towards the bottom of the shield

Insert the SIM with the gold pads facing up and the notch on the outer corner

Close the hinge down and slide the cover to lock it in place

The SIM should be secure and flat in the holder

The FONA library is under heavy development! This page may change over time!

Download Adafruit_FONA

Open up the Arduino library manager

Search for the Adafruit FONA library and install it

We also have a great tutorial on Arduino library installation at:

FONA 3G Baud Adjustment

If you have a FONA 3G, the first time you use it you may need to run the FONA3G_setBaud example to set the baud rate manually to 4800bps rather than 115200

Load Demo

Open up File->Examples->Adafruit_FONA->FONAtest and upload to your Arduino wired up to the module.

For the FONA 3G, change the constructor used in FONATest to Adafruit_FONA_3G:

// Use this for FONA 800 and 808s
//Adafruit_FONA fona = Adafruit_FONA(FONA_RST);
// Use this one for FONA 3G
Adafruit_FONA_3G fona = Adafruit_FONA_3G(FONA_RST);

For Mega, Leonardo, or Micro, change the definition of FONA_TX to the pin you used!

Make sure you have a charged 3.7/4.2V LiPoly or LiIon battery plugged into the JST and an antenna attached
Once uploaded to your Arduino, open up the serial console at 115200 baud speed to begin the tester sketch
Make sure you also have Both NL & CR for the serial command sender option. This means when you send data to the Arduino via the console, it will put a newline/return at the end.

Using the Test Sketch

The test sketch has a menu interface so you can test out just about everything the FONA can do. The menu may change slightly as we add more functionality and update code!

Continue onto the next few sections to see what functionality you can test with the sketch

Battery voltage

Lets begin by reading the battery voltage. That's the lipoly battery. This is handy if you need to track when the battery is low! type b into the command window and hit Send

You'll see a print-out of the battery voltage in mV, so in this case its 3.726V


You can verify that the SIM is inserted and correct by reading the CCID, which is the unique identifier printed on it with C

Check RSSI (network signal strength)

You can ask the FONA for the signal strength with the command i. The reply is a number, but you can convert it to dBm. Try to have the signal strength higher than 5 in order to make calls, SMSs, etc. In this case, I've got a 10

Checking Network Registration

If the FONA has good signal it will immediately try to locate a cell tower and register to it.
You can check the status of the network with n
Once it's Home Registered, give it like 5-10 more seconds before trying to access/send SMS's or phone calls.

Set and Get audio volume

You can set the audio volume with v and retrieve it with V - its in % so ranges from 0 to 100

Setting Headset or External audio

There are two audio paths on the FONA. One is the headset, thru the 3.5mm audio jack. The other is "external" - using the two speaker and mic pins for wiring up external speaker and mic. FM audio, phone calls, tones, etc can be routed to one or the other.
To set the audio to headset, use the command H
To set the audio to external, use the command e

Note the FONA 808 only has Headset audio, so setting External audio wont do anything. The Feather FONA does not have headphone brought out, so use external only!

Playing Toolkit Tones

You can test the audio path with the toolkit tones. These are tones that mimic what some phone services sound like. For a full list of tones, you can check the AT+STTONE command in the AT command datasheet. We'll use tone #20 which is the American dial tone.
You can switch to headset mode, play a tone, then try it on the external audio mode. This is a very easy way to try out both speakers for debugging

PWM Buzzer is available on the FONA800 and 808 Breakouts and Shields


There is a single PWM output pin that you can use to control a Piezo or a vibrating motor. The datasheet is a little unclear on how to use it in 'PWM' mode where you have full frequency and duty cycle control. In the mode we're using it, you can set the frequency from 1-2000 Hz and it will have 50% duty cycle. The PWM pin is the straight-from-the-module output, 2.8Vpp. The Buzzer pins have a PNP driver, so you can use it with a motor buzzer and power from the lipoly battery.

Make Phone Calls

OK now we're onto the good stuff. You can make a phone call with FONA pretty easily. Make sure you have the right audio interface selected (external or headset!) before you go forward

Make a call with c - the call happens in the 'background'. When you're done then you can hang up with h

Send and Read SMS

Another easy thing you can do is send and receive SMS messages. Lets start by sending an SMS. We'll use twitter's 40404 short code, which will auto respond, making it easy to verify both sending and receiving

You can send multi-line SMS's using the library API but for this example, its easier to parse the data if its a single line!

You can then ask the SIM how many SMS's it has with N and read all of them with R

Note that SMS's are referred to by slots but the number does not include empty slots. We'll show this in detail in a bit

You can read individual SMS's with r

And delete SMS's by slot # with d

Note that before I deleted SMS #2, so if I read them again, that SMS # will be an empty slot. SMS number #3 doesn't "move slots"!

GPS Submodule (FONA 808 only)

The FONA 808 has a built in GPS module, you can use it for locating yourself in space! You will need to attach a GPS antenna to the uFL connector and make sure the GPS antenna is outside and pointing up to towards the sky

Make sure to use a PASSIVE GPS antenna!

You can start out by turning on the GPS module with O (capital-o) and query the status of the 'fix' with x. It will take a minute or two to get a fix.

On FONA808 v1's the commands follow the AT+CGPSxxx pattern, on the v2's the commands are similar but look like AT+CGNSxxx

Once you have a fix you can query and get the location/time data with L

The data is in a comma-seperated format:

Can  be parsed out to:

  • 0 - this is the mode (will be 0)
  • 4043.576433 - this is the longitude
  • 7400.316980 - this is the latitude
People often get confused because the GPS is working but is "5 miles off" - this is because they are not parsing the lat/long data correctly. Despite appearances, the geolocation data is NOT in decimal degrees. It is in degrees and minutes in the following format: Latitude: DDMM.MMMM (The first two characters are the degrees.) Longitude: DDDMM.MMMM (The first three characters are the degrees.)
  • 58.647405 - this is the altitude in meters
  • 20150601201258.000 - this is the UTC time in yyymmddHHMMSS.ms format. E.g. this is year 2015, month 06, date 01, 20 hour, 12 minute, 58 seconds.  If you are not in UTC timezone you'll have to adjust this for your local time
  • 64 - is the ttff, time to first fix, in seconds
  • 12 - is the # of visible satelites
  • 0.548363 - is the speed (in knots)
  • 100.442406 - this is the best guess for 'course', e.g. which way you are heading, with 0 being 'north' and 180 being 'south' (we think)

Raw NMEA out

If you want to get the 'raw NMEA' data for some reason, you can do that with E 

On V1 FONA808's you can send a number from 0-255 indicating which sentences you want emittted.

  • 0 for disable output
  • +2 for $GPGGA
  • +4 for $GPGLL
  • +8 for $GPGSA
  • +16 for $GPGSV
  • +32 for $GPRMC
  • +64 for $GPVTG
  • +128 for GPZDA

e.g. if you want to see GPRMC and GPGGA, add +32 and +2 = 34 and put in that number. Then you'll see the data stream out at 1Hz

On V2 FONA's you can only select 'on' or 'off' and get all sentences!

When done, you can type in E and 0 instead, which will turn off the output

Here's a quick list of useful commands that may not be directly supported by the library but are handy for many projects!

RI on SMS receipt


The RI pin will pulse low for ~100ms when an SMS is received

Factory Reset


will reset the FONA GSM module to its factory default

Bluetooth commands

Here's a thread if you're interested in the BT support in the SIM800H (there's no antenna for BT in the SIM800 breakout but it is in the FONA feather)

We have two different types of GSM modules & shields under the FONA brand name. The FONA 800 (GSM/GPRS)

and the FONA 808 (GSM/GPRS + GPS too)

Here's the key similarities

  • Both have a 2G GSM/GPRS cellular core
  • Both can do voice, data, text
  • Both require a LiPoly battery and GSM antenna
  • Both can use a 3.5mm headset
  • Both recharge over the microUSB jack
  • Both have a buzzer driver

Here's key differences

  • Size: the SIM808 based FONA breakout is larger. Shields are the same size
  • The 808 has a GPS module integrated as well
  • The 800 has external 8 ohm speaker driver (external audio) whereas the 808 has only headset audio and 32 ohm speaker driver
  • The 800 has an FM tuner for listening to radio
Is a Lipo Battery required? Can I run the FONA off of a power supply or just the microUSB port?

The microUSB (on the shield, in CHARGE mode and powered via USB or DC power) is only used to charge the battery. Without a battery installed it will flicker on and off so it cannot be used to power a FONA minus battery.

A 1200mAh+ sized Lithium ion/polymer battery is required, nothing else will be able to easily power the FONA and provide the correct voltage range even during 2 Amp spikes.

I really want to run my FONA without a Lipoly battery!

You can't.

We keep getting people who ask "Hey I know its a requirement but I want to build a buck/boost/linear 3.8V regulator and it wil be OK because I said so" and then they realize it doesn't work well

The FONA design depends on a Lipoly battery. The battery is not optional. The battery is essential to function. If you do not want a Lipoly battery you will have to use a different cellular module design. All of our FONAs require, depend and will not work without a Lipoly battery

You can keep the battery topped up with an external 5V power supply for long term usage but the battery is still required even if plugged into USB

Ahh! My FONA was working fine then I sent it some command and its not working right anymore?

You can always factory reset the FONA by sending it the


command. Say with fona.println("ATZ") or using a USB console cable to send commands. If you set an odd fixed baud rate (e.g. you cannot even get an OK when you send AT), a USB serial console cable will be helpful it quickly changing baud rates in your terminal software to get back to a working AT/OK setup!

I'm using FONA as a voice caller and the other person can't hear me!

Note that you do have to use a compatible headset. Not all CTIA headsets will work, the ones we have in the shop are known to work and so do many other Android but iPhone headsets do not.

You can also use 'external' audio on the FONA (electret mic and speaker soldered to FONA) but you cannot mix and match. Either you use headset or you use external audio. You cant use external mic and headset speaker.

You also have to tell the FONA which audio you are using, it does not autodetect. You can use our library and fona.setAudio()

My FONA doesn't work with Arduino Due/ADK/101/Galileo/STM32....

Right now we only know that the FONA library and shields work with Arduino UNO. Any other platforms may require porting work

Can I charge the battery and use FONA at the same time?

Yes! You can use the Lipoly as sort of a 'backup battery' - keep charging it via MicroUSB (on the shield, in CHARGE mode and powered via USB or DC power) during use. If the MicroUSB loses power, the FONA will keep going.

My FONA won't turn on/respond! Or it acts flakey and auto-shuts off sometimes!

We've noticed a lot of problems that are 'weird' that are a results of using batteries with the wrong polarity.

All batteries from adafruit have the right wire colors/polarity for the FONA

Batteries not from Adafruit are not guaranteed to have the right pinout! Using the wrong pinout may damage the FONA and/or make it act 'odd'!

FONA 800/808 requires a 2G SIM, does it work with a dual 2G-3G SIM?

That will work fine, as long as the SIM can register to the 2G network at all, it is acceptable to use

Are you sure I can't use ATT for 2G service? I'm in a T-Mobile cold spot

The AT&T GSM network is going to be live until January 2017. If you're reading this and it's 2017, you're outta luck. If not, you can try to get an AT&T SIM activated to the 2G GSM network but its not going to do that by default. You'll have to call up or talk to an AT&T rep and it may not go so well because they really don't want people to use their GSM network.

You can also call up T-Mobile and say you can't get connected consistently - they may send you a free signal booster

Check out this handy map to see T-Mobile's coverage map in the USA

How long can FONA last on my battery?
We haven't done extensive testing with FONA but from preliminary reports, the FONA draws about 20-25mA while running, up to 200mA+ while actually making a call/sending/receiving data, and has very small spikes of up to 2A. The spikes are short and are absorbed by the onboard capacitors.

A 1200mAh battery can run the FONA on 'standby' for a day or two.
How do I set the Real Time Clock on the FONA SIM?
Please see this forum post!

I'm using a FONA 808 and the GPS commands aren't working

The FONA 808 has two versions, due to a revision of the module itself. Version 1 has two barcodes on the front and is part #S2-10606-Z1F01. Version 2 has a QR code on the front and is part #S2-10606-Z1F02. V2 has a newer/better chipset (MT3337 instead of MT3336) but the commandset has changed. Which is annoying but adaptable!

If you are using V1, use this GPS command document for how to interact with the GPS subsystem

If you are using V2, use this GNSS command document instead.

How do I switch between SMS storage on SIM and in internal FLASH?

You can switch between the storage locations by changing the FONA_PREF_SMS_STORAGE definition in the Adafruit_FONA.h library file.  The definition "SM" selects the SIM, and the definition "ME" selects FLASH.

// Set the preferred SMS storage.
//   Use "SM" for storage on the SIM.
//   Use "ME" for internal storage on the FONA chip
//#define FONA_PREF_SMS_STORAGE "\"ME\""

Then recompile and upload

I'm trying to reset the FONA with my microcontroller/computer and pulling the RESET pin low via a GPIO isnt working?

There's a superfluous level shifting diode that we put on the FONA and FONA 808 breakouts - it turns out it isn't necessary and for microcontrollers with weaker outputs it can keep the FONA from resetting.

You can 'bridge' this diode with a piece of wire, its perfectly safe and may give you a little more headroom. There's already level shifting inside the modules so there's no risk to this mod.

Simply solder a small wire between the two pads, or remove the diode and replace with a 0 ohm resistor or wire.

See more here: http://forums.adafruit.com/viewtopic.php?f=54&t=77778#p410867

This guide was first published on Jul 17, 2015. It was last updated on Mar 08, 2024.