Recipes

Scope: four small builds that combine the previous chapters into the shapes real flows take. Each is described as a wiring list; all the parts are ones the lab ran.

1. The five-minute heartbeat

Know within minutes when a machine goes quiet.

[inject: every 5 minutes] ─▶ [http request: the machine's page]
                          ─▶ [switch: status not 200]
                          ─▶ [mqtt out: alerts/heartbeat]

The inject node repeats on a schedule as happily as it fires by hand, and the switch node does the judging without a line of code. Publish only failures, or the alert channel teaches everyone to ignore it.

2. A form on the wall

A web page button that does one thing in the house.

Chapter 5's /hello pattern, pointed inward: an http in at /porch (chapter 8's actual flow) that publishes one MQTT message and answers the browser. Laminate the address into a QR code by the door and the porch light has a web switch. Remember chapter 9: that endpoint is open to your network unless you planned otherwise.

3. The daily note, kept by the house

Chapter 7's file flow, on a timer.

[inject: 07:00 daily] ─▶ [http request: weather or a sensor API]
                      ─▶ [function: one line, stamped]
                      ─▶ [file: append to notes.txt]
                      ─▶ [http in /notes] serves it back

The lab wrote kettle notes by hand; scheduling the writer and serving the file over HTTP are the same nodes in a different order. A year of these lines is a genuinely pleasant artefact.

4. Count, remember, report

Chapter 7's counter, grown up.

Any event — an mqtt in on a door sensor, say — increments a flow-context counter. A second flow reads the counter on request (the lab's /presses), and a third resets it at midnight with an inject and a change node. With persistent context on, the count survives restarts; with it off, it doesn't, and now you know which behaviour you're choosing and why.