Thermal Printer Part 2: Adding AI and a Web Interface

At the end of Part 1, I had a working thermal printer. Images printed fast. The BLE protocol was figured out. Victory.

But it still required SSH-ing into a Raspberry Pi and running Python scripts manually.

Not exactly something I could hand to a friend and say “here, print something fun.”

The obvious next step

I wanted two things:

1. Generate images with AI — type a prompt, get a weird little print
2. A web interface — so anyone on my network could use it from their phone

The first part meant calling an image generation API. I went with Google’s Gemini — mostly because I already had an API key lying around.

The second part meant Flask. Simple, boring, perfect.

Just like Part 1, Claude Code did most of the heavy lifting here. I described what I wanted, and it wrote the Flask server, the HTML, the JavaScript — all of it. My job was mostly pointing it in the right direction and testing things on the actual printer.

The whole thing is embarrassingly simple

Here’s the basic flow:

1. User opens a webpage on their phone
2. Types something like “a cat wearing a tiny hat”
3. Hits print
4. Gemini generates the image
5. The Pi processes it and sends it to the printer over BLE
6. A grainy, slightly cursed cat-in-a-hat emerges from the printer

The web UI is maybe 50 lines of HTML. One text input. One button. A status message.

@app.route('/print', methods=['POST'])
def print_image():
    prompt = request.get_json().get('prompt', '')

    # Generate image with AI
    generated_img = generate_image(prompt, API_KEY)

    # Prepare and print
    img = prepare_image(generated_img)
    # ... send to printer over BLE

That’s really it.

The fun part

What makes this actually enjoyable isn’t the code — it’s what happens when you use it.

You type a prompt. You wait a few seconds. And then this tiny printer spits out something that looks like it came from a 1990s fax machine, except the content is completely unhinged because an AI generated it.

There’s something weirdly satisfying about holding a physical printout of something that didn’t exist 10 seconds ago.

My friends started requesting increasingly absurd prints. My personal favorite: “a programmer telling his manager it works on my machine.”

Each one took about 5-6 seconds. Type, wait, print. Repeat.

What I actually built

The server runs on the Pi. It listens on port 5000. Anyone on my home network can hit it from their browser.

export GOOGLE_API_KEY='your-key-here'
python3 web.py

That’s the entire deployment.

No Docker. No nginx. No SSL. Just a Flask app running on a Raspberry Pi connected to a $15 thermal printer.

Sometimes the best version of something is the simplest one that works.

What’s next

Honestly? Probably nothing.

This project is done in the way weekend projects are done — it works, it’s fun, and I’ve already moved on to thinking about something else.

But if I were to keep going:

• Add JBIG compression (the thing the Android app uses) for even faster prints
• Let people upload their own images instead of just generating them
• Make a little enclosure so the printer doesn’t just sit on my desk looking chaotic

For now though, I’m happy. I learned BLE. I reverse-engineered a cheap printer. I made something my friends can actually use.

That’s a good weekend.