Transitioning from Arduino to nRF52840 for IoT Application Development

[frusciante89]

Hello Nordic Community,

I am currently working on a project that involves transitioning from a working Arduino application to a finished IoT application targeting Garmin-style devices to display acceleration and velocity data. I have some background in both software and hardware development and have purchased the Nordic nRF52840 Evaluation Board to facilitate this transition.

I would like to seek your advice on the recommended steps to make this transition smooth and efficient. Specifically, I am interested in:

1. SPI/I2C Communication: Any guidance on setting up SPI communication with accelerometers and other sensors.

2. Data Handling: Best practices for reading and processing acceleration and velocity data from sensors.

3. Bluetooth Communication: How to establish Bluetooth Low Energy (BLE) communication with Garmin-style devices, including any example code or libraries.

4. Power Management: Tips on optimizing power consumption, especially for battery-operated applications.

5. Development Tools: Recommended tools and IDEs for development with the nRF52840, along with any libraries that may help streamline the process.

6. Testing and Validation: Suggestions for testing my application, particularly for ensuring reliable communication and accurate data readings.

Any insights or resources you could share would be greatly appreciated, as I aim to create a robust and efficient application.

Thank you in advance for your help!

AA

[GokulPrasanth]

Try start learning from Nordic Developer Academy

[Edvin]

Hello,

I agree that the DevAcademy might be the correct starting place. 

To be specific, I suggest that you run through these courses, in this order:

1: nRF Connect SDK Fundamentals

2: Bluetooth Low Energy Fundamentals

3: nRF Connect SDK Intermediate

The first one to familiarize yourself with the SDK and the tools required to use our chips and Development Kits.

The second one to familiarize yourself with the Bluetooth Low Energy (BLE) libraries, and how BLE works in general.

The third one is mainly if you want to look at how to set up SPI. I2C is covered in the first one, but if you want to communicate with an SPI device, there is a lesson in there showing how to do that. 

Best regards,

Edvin

[frusciante89]

Hi Edvin,

Thank you so much for your help! Over the last few days, I’ve been diving into the SDK fundamentals and wanted to provide some additional details about my project.

Project Overview:

• My goal is to develop a Garmin-compatible device (ATN+) that can measure acceleration, velocity, and force.
• I plan to use an accelerometer/gyroscope (LSM6DSO) and two ADS1220 chips to read data from four strain gauges.
• Since the PCB needs to fit into a small space within the device, minimizing the circuit’s footprint is essential.
• Power will be supplied by a LiPo battery.

Development Progress:

1. Component Selection: After selecting sensors, I chose the nRF52840 as the microcontroller since it offers ATN+ compatibility and seems ideal for this application.
2. Sensor Testing: I tested the sensors using an Arduino and successfully collected the expected data.
3. nRF52840 Development Kit: I sourced the dev kit to transition from Arduino to the nRF ecosystem and am currently getting familiar with Nordic’s SDK.
4. Next Step: Connect all sensors to the board (preferably via SPI) and verify I’m reading meaningful data.
5. Next Step: Develop the Bluetooth/ATN+ communication, ensuring I can transmit and receive data, which will validate the whole stack.
6. Next Step: Design a custom PCB featuring the nRF52840 and the aforementioned sensors, phasing out the dev board.
7. Next Step: Switch from USB power to a LiPo battery and incorporate a battery charging circuit.

Questions:

1. SPI Configuration: I plan to use SPI to connect the accelerometer/gyroscope and both ADS1220 chips, with the nRF52840 acting as the master. Is it feasible to have all three devices on a single SPI bus, or would separate channels be a better option? Are there any examples or resources you can point me to?

2. Logic Levels: It looks like the nRF52840 operates at 3.3V logic, which eliminates the need for level shifters (a necessity in my Arduino prototype). Can you confirm if this applies both in USB mode and when using the LiPo battery in the final design? I want to avoid any electrical mishaps!

3. Advice from the Community: If anyone has gone through a similar process, I’d greatly appreciate any tips or things I should look out for during development.

Thanks in advance for your insights!

[Edvin]

frusciante89 said:

Development Progress:

Sounds reasonable.

You can also test with a battery by powering the nRF via the Li-Po connector. You can also measure the current using the Power Profiler Kit II, to calculate how long the device will last on a battery charge. 

I have not played too much around with it yet, but you can also look into the nPM Fuel Gauge. I believe you can use the nPM1300 for this, but this is not my area of expertise, but we have some development kits for this. 

frusciante89 said:

SPI Configuration:

You can use one bus (as long as they can run on the same SPI frequency). Then you just need one additional GPIO per device (chip select pin). 

frusciante89 said:

Logic Levels: It looks like the nRF52840 operates at 3.3V logic, which eliminates the need for level shifters

The output voltage on the GPIOs is dependent on the REGOUT0 register. So you can set it to values ranging from 1.8V to 3.3V. This is regardless of what the input voltage you have, and what source this is coming from. Please note that on the nRF52840 DK there is some external hardware that sets the output voltage on the GPIOs to be fixed when the "nRF Power Source" switch is set to VDD. So the nRF's output voltage is controlled by the REGOUT0 register, but the voltage on the pin header is scaled up to 3.3V. If you set the nRF Power source" switch to USB or LiPo, then the output voltage on the GPIO headers will follow the REGOUT0 register settings.

Best regards,

Edvin

[frusciante89]

Dear Edvin, 

thanks a lot! 
I've spent last week having a look at the Nordic Developer Academy course, which helped a lot!
I am now able to sample all sensors, only thing missing is the bluetooth connectivity part (I'll start tackling next week) and the battery power config.

In preparation for the next steps, my main question is:

• how do I move from the nRF52840 dev board to my custom PCB? I want the keep the minimum amount of components while obviously being able to program my board and flash the firmware.

Some specific doubts: 

1. in my custom PCB, how can I program with same toolchain (currently using nRF52840DK + VSCode)? Do you have an example of how this can be implemented? Do I just need to include in my PCB a debugging connector through the SWDIO, SWCLK, VDD, and GND pins? 
2. Is it ok/feasible to use a 2 layers PCB for the QIAA package?
3. in the production version of the board, should flashing/debugging be done through a USB or through the debug header?
4. Do I need to add a memory/EEPROM to my PCB? Or can the flash memory of the nRF52840 be enough? I do not need to save anything in particular apart from the program itself that runs on the nRF chip and a couple of register settings for my sensors
5. once I manufacture the PCB, can I use the nRF52840 DK as the debug/flash "master"? Or do I need a JLink device to connect to my PC?
6. When programming an external board with the nRF52840 DK, will the nRF52840 DK provide power to the target and will the target need its power (through the LiPO). Just making sure I have no conflicting power sources 
7. the board power will be supplied by a LiPO battery in the production version. In the hypothesis that all flash/debugging can be done through the debug header, I assume no USB power will be needed, apart from charging the battery?
8. As the USB will be needed to charge the LiPO, can you point me to any reference circuit to be able to do that? I had a look at the Thingy:53 charging circuit, but it looks like you have to manually set the power source. Can this be done automatically without the user having to flip a switch?
9. For reference, it would be ideal to have all GPIOs running at 3V3 High level. I hence assume the power rail of entire PCB should be running at 3V3
10. As I will be using the Bluetooth and ATN connectivity features, is there anything to consider/add apart from the antenna design? Does the power architecture changes when using Bluetooth/ATN? (I will not be using NFC)
11. For my sensors, as I'm using both I2C and SPI, I've selected the following GPIO (I've tried to avoid the low speed ones). Does this mapping look good?
    1. I2C (SCL) - 0.26
    2. I2C (SDA) - 0.04
    3. SPI (DRDY) - 0.13
    4. SPI (CS) - 0.15 
    5. SPI (CLK) - 0.17 
    6. SPI (MOSI) - 0.22 
    7. SPI (MISO) - 0.24  
12. Are pull-up resistors needed for the I2C pins? I remember reading that there are internal pullups already present?

Also, just to confirm my dev flow is correct, I've been using the nRF52840 DK to develop my application, but some doubts arose:

• I've noticed the board has both the nRF52840 and nRF5340 chips (marked as U1 and U2) implemented, I assume the nRF5340 is used as a middle-man in the DK board? I guess I can skip it in my custom PCB? Also, I've been using the USB IF MCU port to work on the nRF52840, is this correct? I've just noticed there's another USB port, named USB nRF52840 - should I use this instead?

Thanks again, I'm learning a lot and sorry if I asked silly question, I really want to make sure I get this right 

Best

AA