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Plotting Data on Your Computer

Your robot logs CSV files to the Pico's filesystem. To analyze and plot them, you download the files and run Python scripts on your computer (not the Pico). This page explains how to set up and use this workflow.

One-Time Setup

1. Check if Python is installed

Open a terminal on your computer (not the Pico REPL!) and run:

python --version

You should see something like Python 3.10.12. If you get "command not found", try python3 --version.

Installing Python
  • Windows: Download from python.org. During install, check "Add Python to PATH".
  • Mac: brew install python3 or download from python.org.
  • Linux: Usually pre-installed. If not: sudo apt install python3 python3-pip (Debian/Ubuntu) or sudo pacman -S python (Arch).

2. Install matplotlib

pip install matplotlib

If that doesn't work, try one of these:

pip3 install matplotlib           # Some systems use pip3
python -m pip install matplotlib  # Explicit Python module call
pip install --user matplotlib     # No admin rights

3. Verify it works

python -c "import matplotlib; print('matplotlib OK:', matplotlib.__version__)"

You should see matplotlib OK: 3.x.x. If you get an ImportError, the install didn't work — try the alternative pip commands above.

The Workflow

Every time you want to plot data from the robot:

┌─────────┐     ┌──────────┐     ┌──────────┐     ┌──────────┐
│  Robot   │────►│ Download │────►│  Plot    │────►│ Analyze  │
│ logs CSV │     │ to PC    │     │ script   │     │ the chart│
└─────────┘     └──────────┘     └──────────┘     └──────────┘

Step 1: Download the CSV from the Pico

In your terminal (not the Pico REPL):

mpremote cp :filename.csv .

The : prefix means "on the Pico." The . means "save to current directory on my PC."

List files on the Pico 

mpremote ls
This shows all files on the Pico, including your CSV logs.

Step 2: Save the plot script

Each tutorial provides a plot script. Save it as a .py file on your computer, for example plot_data.py.

Step 3: Run the script

python plot_data.py

A window opens with the chart. You can:

  • Zoom — click the magnifying glass icon, then drag to select a region
  • Pan — click the move icon, then drag
  • Save — click the floppy disk icon, or the script saves a PNG automatically
  • Close — close the window to return to the terminal

Minimal Plot Template

Use this as a starting point for any CSV data:

import csv
import matplotlib.pyplot as plt

# --- Load CSV ---
data = {}
with open("your_file.csv") as f:
    reader = csv.DictReader(f)
    for col in reader.fieldnames:
        data[col] = []
    for row in reader:
        for col in reader.fieldnames:
            data[col].append(float(row[col]))

# --- Plot ---
plt.figure(figsize=(10, 4))
plt.plot(data["time_ms"], data["error"], label="Error")
plt.xlabel("Time (ms)")
plt.ylabel("Error")
plt.title("My Robot Data")
plt.legend()
plt.grid(True, alpha=0.3)
plt.tight_layout()
plt.savefig("my_plot.png", dpi=150)
plt.show()

Change the column names (time_ms, error) to match your CSV headers. Add more plt.plot() lines to overlay multiple signals.

Multiple Subplots

fig, axes = plt.subplots(2, 1, figsize=(10, 6), sharex=True)

axes[0].plot(data["time_ms"], data["error"])
axes[0].set_ylabel("Error")
axes[0].set_title("Top chart")

axes[1].plot(data["time_ms"], data["pwm"], color="orange")
axes[1].set_ylabel("PWM")
axes[1].set_xlabel("Time (ms)")

plt.tight_layout()
plt.savefig("multi_plot.png", dpi=150)
plt.show()

Comparing Multiple Runs

for filename in ["run1.csv", "run2.csv", "run3.csv"]:
    data = load_csv(filename)  # Use the load function from above
    plt.plot(data["time_ms"], data["error"], label=filename)

plt.legend()
plt.show()

Troubleshooting

Problem Solution
ModuleNotFoundError: No module named 'matplotlib' Run pip install matplotlib again. Make sure you're using the same Python that you run scripts with.
python: command not found Try python3 instead, or install Python.
mpremote: command not found Run pip install mpremote.
mpremote cp gives error Make sure the Pico is connected via USB and no REPL session is open.
Plot window doesn't appear On some systems (WSL, SSH), try adding plt.savefig("plot.png") before plt.show() and open the PNG manually.
CSV file is empty or garbled Check that the robot code finished cleanly (reached f.close()). If you hit Ctrl+C during logging, the last line may be incomplete — delete it from the CSV.

No matplotlib? Alternatives

If you can't install matplotlib:

  • Google Sheets: Upload the CSV, select columns, Insert → Chart
  • Excel / LibreOffice Calc: Open the CSV, select data, Insert → Line Chart
  • Online: Paste CSV data into csvplot.com

These work for quick visual checks. For systematic tuning (overlaying multiple runs, annotating), matplotlib is worth the setup.