Cardano Doorbell

Most blockchain demos happen on screens — a wallet balance updates, an explorer page refreshes. Nothing about that feels real. The Cardano Doorbell was built to make decentralization physical: someone sends a transaction from anywhere in the world, and a light turns on in a room in Uyo.

The trigger isn't a webhook or a company's push notification service. The Pico W reads public chain state directly. If Blockfrost disappeared tomorrow, the same script could point at any other Cardano API — or eventually a local node — because the data itself lives on-chain, owned by no one.

It was built as the centerpiece demo for Pi Jam Uyo Vol. 2 — Hardware Corner (July 31, 2026): a live demonstration where attendees send a tagged transaction and watch the LED respond seconds later.

[Eternl wallet, anywhere]
        |
        |  tx with metadata "PIJAM"
        v
[Cardano preprod chain]
        |
        |  polled every 10s via Blockfrost
        |  /addresses/{address}/transactions
        v
[Raspberry Pi Pico W]
        |
        |  metadata parsed, tag matched
        v
[Onboard LED — 3 seconds]

The script polls one specific known address — it is address-scoped, not scanning the whole chain. When a new transaction appears, it fetches the transaction's metadata and checks for the "PIJAM" tag.

Metadata detection is wallet-agnostic. It handles three formats:

• Plain string (Eternl's free "Add on-chain Message" feature)
• List of strings
• Proper CIP-20 {"msg": [...]} dict format
• Plus a raw-string fallback across the entire metadata response

A METADATA_FILTER toggle switches behavior: True = only trigger on "PIJAM"-tagged transactions, False = trigger on any new transaction (plain tip-jar mode).

There are two versions of the firmware:

• cardano_doorbell.py — the core: poll, match, blink
• cardano_doorbell_with_status.py — additionally serves a local status webpage on the same WiFi network, auto-refreshing every 5 seconds, showing: status, watched address, last poll time, last tx hash, tag match result, LED state, poll/trigger counts, and uptime

Hardware

That's the whole BOM. The point is minimalism — chain state to physical output with the least hardware possible.

Setup

1. Create a free Blockfrost account and a PREPROD project — the project_id is passed as a request header
2. Install Eternl wallet, switch it to the Preprod network, fund it via the official Cardano testnet faucet
3. Flash MicroPython onto the Pico W
4. Copy cardano_doorbell.py across, set your WiFi credentials, Blockfrost project ID, and the watched address
5. Run it. Send a transaction to the watched address with "PIJAM" in the metadata (Eternl: "Add on-chain Message"). Watch the LED.

Config values

• METADATA_FILTER — tag-gated vs any-transaction mode
• Poll interval — default 10 seconds
• LED duration — default 3 seconds

• On-chain metadata is messier than the CIP suggests — every wallet writes it slightly differently, which is why the parser handles three formats plus a fallback. Robustness against wallet variance mattered more than elegance.
• MicroPython's TCP stack gets fragile when the Pico W is simultaneously polling Blockfrost and serving HTTP. The _with_status version needs bench-testing under concurrent load before live event use — flagged as the main open risk.
• The demo lands harder than dashboards ever do. "The blockchain turned on a light" is instantly legible to a non-technical audience in a way that explorer screenshots are not.

• [ ] Bench-test cardano_doorbell_with_status.py under concurrent load (WiFi polling + HTTP serving + Blockfrost calls)
• [ ] blink.py starter script for the event's hands-on session
• [ ] README.md and SETUP.md for the repo
• [ ] Live deployment: Pi Jam Uyo Vol. 2 — July 31, 2026
• [ ] Long-term: point at a local Cardano node instead of Blockfrost for full decentralization