Nano RP2040 Datalogger with MicroPython

Learn how to save data in .csv format on the Nano RP2040 Connect, using MicroPython.

Introduction

The Nano RP2040 Connect board has on-board storage that allows you to turn the device into a data logger without any extra components.

In order to utilize this feature, we need to install the latest release of OpenMV's flavor of MicroPython.

This tutorial can be completed with only the Nano RP2040 Connect board and open-source software.

If you are unfamiliar with Arduino & Python, you can learn more by reading the Python with Arduino and the Nano RP2040 Connect Python API Guide articles.

Goals

The goals of this tutorial are:

  • Install OpenMV MicroPython firmware on the board.
  • Learn how to save data in a
    .csv
    format directly on the Nano RP2040 Connect.

Hardware & Software Needed

Install MicroPython

1. The first step is to install the latest version of the OpenMV firmware (MicroPython) on the Nano RP2040 board. This version is available through the link below:

2. Unzip the contents, and locate the

firmware.uf2
file inside of the ARDUINO_NANO_RP2040_CONNECT folder.

3. Force the bootloader on the Nano RP2040 Connect, by connecting a jumper wire between

GND
and
REC
pins as shown in the image below. When the mass storage device opens, drag the
firmware.uf2
onto it, and the latest version will install.

Connect GND + REC + press the reset button to open mass storage.
Connect GND + REC + press the reset button to open mass storage.

4. Install and open the Thonny IDE. Navigate to Run > Select Interpreter and choose the "MicroPython(generic)" from the list. Your board should now appear in the other dropdown menu:

Thonny board/port selection.
Thonny board/port selection.

If your board appears, it has been successful. In this case, it is called

Board in FS mode (/dev/cu.usbmodem11201)
.

Data Logger Example

Now that the OpenMV MicroPython firmware is installed on your device, and it is detected using Thonny, we can create our datalogger.

The script for the datalogger is quite basic, and has the following functionality:

  • Create a
    .csv
    file
  • Read the value of an analog pin, and log it, using the
    file.write()
    function.
  • Repeat 25 times and then finish script.
  • Each time a reading is recorded, the built-in LED flashes.

Code

The script for this tutorial can be found below:

1import machine
2from machine import Pin
3import time
4
5adc_pin = machine.Pin(29)
6adc = machine.ADC(adc_pin)
7led = Pin(6, Pin.OUT)
8readings = 0
9
10# create a file named "data.csv"
11file=open("data.csv","w")
12file.write("data"+"\n")
13
14while True:
15
16 led.value(1)
17 reading = adc.read_u16()
18 print("ADC: ",reading)
19
20 time.sleep_ms(100)
21
22 # convert and write the reading from the analog pin
23 file.write(str(reading)+"\n")
24
25 led.value(0)
26 time.sleep_ms(100)
27 readings += 1
28
29 # if 25 readings are done, finish the program
30 if readings >= 25:
31 file.close()
32 break

Copy paste this code into the Thonny editor, and click on the Green Play Button (F5). The values recorded are also printed in the terminal, so we can compare it later. After running, it should look like this:

Thonny IDE, data printed in terminal.
Thonny IDE, data printed in terminal.

When you run the script, the board should now start blinking fast, every 100 milliseconds, and it will do so 25 times (as is specified in the code, the number can be changed).

Accessing Data

Once done, navigate to Finder / Explorer, and locate a drive called "NO NAME". This should now include a

data.csv
file. This contains the 25 readings we just made by running the script.

If you are using a Mac, you may need to change a setting that allows you to see external disks. If you can't see the drive, go to Finder > Preferences and tick the boxes that appear.

The "NO NAME" drive with a data.csv file.
The "NO NAME" drive with a data.csv file.

Congratulations, you have now successfully recorded data and stored it in a

.csv
file onboard the Nano RP2040 Connect.

Please note that you should never open this file whenever a file management operation is ongoing. This will most likely corrupt your file and you won't be able to obtain the data. Best practice is to record the data, wait a little, and then open up the

data.csv
file.

Conclusion

In this tutorial, we turned a Nano RP2040 Connect board into a data logger, without the use of any external components (such as an SD card).

This is an incredibly useful tool whenever you are working with data collection, and the script found in this tutorial can be easily be altered to fit your project.

While we in this tutorial only recorded values from an analog pin, there are many other things to do, such as:

  • Record data from the onboard IMU.
  • Record data from an external sensor.
  • Record events that occurred along with a timestamp (for example, how many times a sensor value's threshold was met).