I’ve done some experiments with the TinyLoRa library (GitHub - adafruit/TinyLoRa: LoRaWAN Library) on attiny85’s in the past. The attiny85 only has 8 kB of flash. The atmega328p of the UNO has 32 kB.
I’d encourage you to give the atmega328p (UNO) another chance! Benefits: Cheap, robust (no problems with 5 V), a lot less complicated than the SAMD21.
I’ve invested a lot of time getting to grips with the SAMD21. Lower level stuff you’d read in the datasheets is lot easier on the AVR chips (atmega328p) than on the SAMD21.
TinyLora is NoGo on V3.
This has been discussed on the Forum already.
Bad advice. RAM and Flash memory on ATmega328 and ATmega32u4 is just too limited for LoRaWAN compliant stacks if you want to use them with SPI LoRa modules. And as already said you will need level shifters for almost everything (LoRa module and most sensors are 3.3V nowadays). You should not use these MCU’s for new LoRaWAN development in combination with SPI LoRa modules where the LoRaWAN stack has to run on the MCU.
I have used logic level shifters, of the bought off eBay type, to connect a LoRa device to a 5V Arduino. On a scope the logic signals looked very marginal, so long term reliability could be doubtful.
I stand corrected. I was unaware about V3 and that it only seems to work with the LMIC library.
About ATmega328p robustness I have to clarify that my point was, that unlike most 3.3 V MCUs, 5 V won’t be critical to it.
I guess flash size wise the ATmega4809 might then be a suitable alternative. I don’t have experience with it. You can try to run the dev boards at 3.3 V or lower. Depending on the frequency the ATMega’s operate between 1.8 V and 5.5 V. It also comes in a DIP package.
The Seeeduino XIAO - Arduino Microcontroller - SAMD21 Cortex M0+ is also on back order - no stock! So still doesnt help with the question " Where are all the samd21 chips"
Unfortunately it has a couple of drawbacks: it’s available only in BGA packaging and there’s a significant amount of external RF circuitry required around the antenna.
@fishbeetle was referring to the SAMR34 chip which is on BGA which is a total PitA for small production runs and almost impossible to place by hand. The RAK4260 is complete and has castellated edges.
Which confirms you may need to add one capacitor and one ESD suppressor, for which they have given values - so not really any “RF circuit” needed. FishBeetle’s node goes straight from the RFC output to the u.FL connector.
I’m just drawing your attention to the total convenience that the RAK4260 brings.
But it is probably not the module you are looking for if you if you want an AT modem type module to talk to from your AVR. Microchip provide an AT code base that you can download on to the module - so you’ll need to ensure you have access to the programming pins.
On the plus side, if you are comfortable with full-on C type programming, you may find you can put your application on the RAK4260 and skip a second MCU. Or have both and get the benefits of both. If you are going to try out the RAK4260, I’d get a breakout board as it provides Dupont/jumper pins you can just hook up as well as the programming pins and an SMA connector.
If you just want an AT style modem module, then the RAK4270 is the way to go - uses the new low power SX1262 and has the RAK AT firmware pre-installed.
Ok, thank you for your explanation.
I really like the format and the all in one approach
I think im not able to make it running as stand alone for now but i’m sure there will be further development in future.
I found the arduino supported bastwan board.
But for now i think i will stick with the SX1276 and a microcontroller.
… you are back right? 
