What is it?

This is a small 0.9 in. x 2 in. ATSAMR34J18 LoRA System-in-Package (SiP) based development board in Adafruit Feather form-factor. All the design and fabrication files can be found on my GitHub (current version is 1.2). Further documentation can be found on my website.

ATSAMR34J18 LoRa SiP is deigned as a separate RF module and is soldered on top of this breakout board (unsoldered version of the kit can be purchased). The RF module consists of all the essential components for the RF matching, RF switching and power filtering parts.

• ATSAMR34J18 LoRA System-in-Package (SiP) based RF module
• ARM Cortex M0+ MCU & SX1276 LoRa Radio
• 256KB Flash, 40 KB RAM
• Power Output: +20.00 (dBm) (Datasheet (DS) value, real output is not tested)
• Frequency Range: 862 to 1020 MHz (DS values)
• Deep Sleep Current: ~1.3 μA
• IO pins: 27
• Module Dimensions: 0.65 in. x 0.55 in. (16.5mm x 14mm)

The Feather style breakout board comes in a breadboard friendly layout and it contains following items.

• Li-Po battery charging IC w/ MCP73831
• Indicator LEDs for Charge (orange), GPIO (red) and Power (blue) (all w/ cut-off jumpers)
• 3.3V low Iq LDO (~4 μA)
• Low-voltage battery cut-off supervisor IC (3V Vbat cutoff)
• USB connector with protection/filtering circuit
• 0.75 A resettable fuse
• Voltage divider for Vbat monitoring (w/ cut-off jumpers)
• SMA and u.FL antenna connectors (default is SMA)
• 10-pin ARM SWD programming header
• Breakout dimensions: 2 in. x 0.9 in. (50.8 mm x 22.8 mm)

Why did you make it?

About a year ago when this SiP was released I was pretty excited to work on it. I then purchased the official SAMR34 Xplained Pro Evaluation Kit. It's a great kit with on board embedded debugger, but it is not very suitable for developing small and low-power LoRa nodes.

Furthermore, SAMR34 comes in a 6x6 mm BGA package and requires handful of carefully selected RF components to work with, which renders it as a not so hobbyist friendly. By designing a small RF module around it and publishing the design files, anyone who needs can incorporate the RF module in their design (as long as it's not for commercial purposes). All the GPIO lines have been broken out and for low-power operations VCC to the RF-switch can also be controlled using the dedicated GPIO line.

What makes it special?

I made the board small, low-power and as versatile as I could for IoT application development. Most of the Adafruit Feather Wings can be used with this board. It is breadboard friendly but can be made into a portable, battery-powered device for solving real world problems.

Some current consumption results for the RF Module only @3.3V input.

• Active Mode (48MHz): ~4 mA
• Active Mode (12MHz): ~840 μA
• IDLE Mode: ~420 μA
• STANDBY Mode: ~26 μA
• Sleepwalking Mode: ~2.5 μA
• Backup Mode: ~ 820 nA

Some more measurement figures for the breakout board alone @3.7V Vbat (w/o the RF Module).

• Power LED ON: ~510 μA
• Power LED cut-off (JP2): ~9 μA
• VBAT monitoring voltage divider cut-off (JP4): ~7.8 μA
• Li-Po charging IC removed (U2): ~5.8 μA
• Battery voltage supervisor IC removed (U3): ~4.8 μA

When the Vbat voltage dips below 3.1V Voltage supervisor IC will disable the LDO and current consumption will be around 4 μA.

Programming options

As a development environment one can choose between Atmel Studio v7 or newly released Mbed OS 5.10 which adds support for SAML21J18A target.

Here are some instructions on how to setup LoRaWAN stack on SAML21 / SAMR34 Xplained Pro boards (applicable to this board) with mbedOS.

If you plan to use Atmel Studio 7 then please follow this installation instructions that I put together to correctly setup the ASF v3 (Atmel-Software-Framework) development environment. Unfortunately ASF v4 with ATMEL START is currently not supported for SAMR34 devices.

The board can be flashed using an ATMEL-ICE or a J-Link SWD programmer/debuggers.

Serial communication with the board can be established either over the Rx-Tx pins (see the documentation page) using USB to Serial converter (i.e. FTDI, CH340G, etc.) or with the on-board USB. To activate the on-board USB as Virtual COM Port (VCP) one should use Atmel USB Device CDC Application example provided by the ASF. There are several VCP example projects with and without the LoRaWAN stack included.

If you have any questions please don't hesitate to contact me. Follow me @azerimaker to get occasional OSHW project updates.