Case study
Fingerprint gate access
An ESP32 with an R307 verifies fingerprints and, over MQTT, tells a second ESP32 to turn on an SSR on the same circuit as the mechanical gate open button. The portal can trigger that same SSR board when you need a manual open.
Why
The reader and the gate opener wiring are not on one board. Two ESP32 nodes over MQTT fit that split without running long cables from the fingerprint sensor to the SSR.
How
The first ESP32 has an R307 fingerprint module. After a verified scan it publishes the result over MQTT. Finger enrollment stays on that reader, not in the portal.
A Python service listens for a good match and sends a command to the second ESP32 to energize a solid-state relay wired in parallel with the existing mechanical gate open button, so the gate solenoid opens the same way as a manual press.
The portal can send open or close commands to the second board when you need manual control.
Where Python sits on the MQTT path — How it All Works.
Also: Finger enrollment is still done on the reader hardware, not in the portal.
ESP32 + R307 fingerprint reader + Solid-state relay (SSR)