LTE IoT Add-On Kit and Arduino IOREF

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jrecchio's picture
jrecchio
Junior(0)

The hardware manual for this chip says that the shield is made to interface with arduino, and that the shield standard is 3.3V. However, the arduino uno is a 5V device. The IOREF pin on the arduino is set to 5V, but the IOREF pin on this shield is connected to 3.3V. Is there a different arduino aside from the uno that has the R3 pinout form factor but runs at 3.3V? It seems like there will be problems using it with an uno at present.

 

LightCollector's picture
LightCollector
Moderator(15)

Hi, The shield was designed to work with the k64f freedom board which is 3.3v.  I am not familiar with the uno board but sometimes 3.3 and 5v can be mixed.  You will need to look into the following:  the compatible voltages for the uno as well as the cell shield schematics and specifically the level translator chips to see if they are compatible.

 

Best Regards.

 

 

teknomike's picture
teknomike
Junior(0)

There are 2 ways to approach this, but neither addresses the biggest issue (more about that later in this comment). You can either use a standard 5V Arduino board plus a "logic level converter" (available on Amazon, eBay and other sources) to perform the conversion from 3.3 to 5 V for each pin -- typically these modules can handle 4 separate pins and you actually only need 2 (TX and RX) for the Arduino to LTE shield interface. Or you can use a 3.3V Arduino board from an alternate supplier (such as the 3.3V "Arduino Pro Mini" from Adafruit or Sparkfun, which always work well, or from alternative suppliers on Amazon or eBay, which have also worked well for me) and connect directly to the LTE shield -- but in this case all your GPIO will be 3.3V and your Arduino board IDE interface also is unique and there are plenty of learning hurdles in there. Plus, the 3.3V Arduino board pinouts are different and don't match the LTE shield -- so you'll be jumpering everything -- and you might end up using a logic level converter anyway to interface to typical Arduino sensors. Unless you have good Arduino expertise, it's easiest to stick with a standard 5V Arduino Uno R3 and work out from there.

But the biggest issue with using an Arduino with this LTE shield is you really need the libraries to simplify control and use of the LTE shield -- otherwise it's a very complicated item indeed -- and I haven't been able to find any such libraries for this board yet. Connection to the LTE network is complicated and specific, and if you don't get it just right your connection will be rejected. The library should have all of this already developed, but so far I can only find libraries for this LTE board that support the Raspberry Pi and ARM MBED environments -- not Arduino. Will comment back here if I find anything.

teknomike's picture
teknomike
Junior(0)

Update -- just found this comment on the FAQ page (https://starterkit.att.com/faq#other-microcontrollers ): "Currently, there is no software library for Arduino itself, however. You could implement your own using the AT Command Guide on the Resources page." Note: that AT Command Guide is huge; probably the best way to determine the proper set of AT commands for specific objectives is to deconstruct what's already in the RPi and FRDM board libraries....