We are using the S2 Lolin mini with circuitpython. It was our hope to build a way to get data off of the device, in a reliable(ish) way. While you can use STDIO and print to the output window (command line) you can’t save to a file without modifications to the device that I wasn’t willing to make. I spent some time on this today and it wasn’t easy. (This is actually a good reason to use a regular raspberry pi with memory.) These are my notes on how I saved data from my device into a CSV file on my computer.

Things that didn’t work

• Adafruit has some built in IoT functionality; however, none of it seemed to work with S2 Lolin mini. However there were many options for the ESP32-S2 which the Lolin chip is based off. We couldn’t make it work quickly enough. So it could also be our fault.
• I considered building an external database and sending messages over the internet. I would normally have gone this way. However, we have a fairly closed internet system on campus and setting up databases and the like isn’t easy to do locally. I spent a little time setting up a database online but got side tracked.
• I screwed around with a couple of other ideas.

I came up with a VERY brittle solution which will work for what we are doing in the short term. Here it is.

Step 1: You can log the shell in thonny. To do this, go to Thonny settings, click over to the general tab, click the “log program usage…” option.

Step 2: Restart Thonny

Step 3: Design a program in Thonny that outputs a regular data output, with a key in front.

For example here we used the key !!!!. So you get a regular output with a string of data. See the shell below:

Notice in the shell with the leading key. This string will be logged in the log file on the host computer. Unfortunately, there is also a bunch of other crap that also gets logged.

counter       = 0
StopCounting  = 100
kHalf         = "!!"

while counter < StopCounting:
    
    Temperature  = counter * 3
    Laser        = Temperature - 7
    
    myStr = kHalf + kHalf + "," + str(counter) + ", " + str(Temperature) + ", " + str(Laser) + ", 0"
    print (myStr)
    
    counter = counter + 1

Unfortunately, you can’t use the key in the code directly, unless you want to do more programming – because that also shows up in the log. And we are just going to search for the key. Again, I was going for the sloppiest most brittle solution. I JUST WANT MY DATA! So I built my key from two peices !! and !!.

Step 4: Parse and save the Log

Based on the recommendation in the following thread, https://forums.raspberrypi.com/viewtopic.php?t=310502 I developed a short python script that is ran on the host computer (I ran it in Sypder because I had it opened.) It goes through the log and looks for the key and then parses the data. Finally the data is stored to a CSV file.

myFile   = 'C:\\Users\\mwright\\AppData\\Roaming\\Thonny\\user_logs\\2023-04-27_16-47-41_0'
f = open(myFile + '.txt','r')


MyKey      = '!!!!'
MyLines    = str('')

try:
    while True:
        line = f.readline();
        if not line:
            break
        if line.find(MyKey)>=0:
            text_value = line.split(',')
            val1 = float(text_value[1])
            val2 = float(text_value[2])
            val3 = float(text_value[3])
            OutToFile = str(val1) + ',' + str(val2) + ',' + str(val3) + '\n'
            print (OutToFile)
            MyLines = MyLines + OutToFile
except:
     pass
            
 
f.close()

g = open(myFile + '.csv','w')
g.write(MyLines)
g.close()

If you run this script it nicely parses the data into a csv file.

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OMG! There has to be a better way! But it works and it does what I need it to do.