Brewery control system

Monorepo of firmware and hardware for an automated HERMS brewery, built around a small fleet of networked temperature probes feeding a central heating controller — all coordinated over MQTT (with Home Assistant discovery, so the whole rig shows up in HA automatically).

Layout: stand_alone_temp_probe/ (RTD probe firmware), boil_controller/ (HERMS/boil controller firmware), brewery_common/ (shared ESP-IDF component: OTA, firmware version-check, network log tap — used by both firmwares via a component-manager path dependency), old/ (reference designs + the original KiCad schematic), tools/ (build helper).

            ┌──────────────────────┐
   HLT  ───▶│ temp probe (RTD)     │──┐
   mash ───▶│ temp probe (RTD)     │──┤   mechination/<id>/temperature
   boil ───▶│ temp probe (RTD)     │──┤      (WiFi, retained, >=1 Hz)
   …    ───▶│ temp probe (RTD)     │──┤
            └──────────────────────┘  │
                                      ▼
                             ┌─────────────────┐
                             │   MQTT broker   │  (+ Home Assistant)
                             └─────────────────┘
                                      │ subscribes to the probe temps
                                      ▼
                       ┌────────────────────────────┐
                       │  boil / HERMS controller   │  ESP32-WROVER
                       │  PID ──▶ ULN2003A ──▶ SSRs │
                       └────────────────────────────┘
                               │            │
                           HLT element   Boil-kettle
                          (heats HERMS)    element

The two firmwares we host here

1. stand_alone_temp_probe/ — temperature probe

Seeed XIAO ESP32-C6 + Adafruit MAX31865 RTD amplifier. Reads a PT100/PT1000 RTD, joins WiFi, and publishes its temperature to MQTT (retained, ≥ 1 Hz) with Home Assistant discovery and RTD-fault reporting. One probe per measured point — give each a distinct device id (hlt, herms_out, boil_kettle, …) so they share the MQTT tree without colliding.

Note: the firmware is WiFi + MQTT (see main/temp_probe.h, idf_component.yml). The probe's own README.md still describes an earlier Zigbee revision and is being updated — trust the WiFi/MQTT build.

2. boil_controller/ — boil / HERMS controller

ESP32-WROVER + ULN2003A + 2× mains SSR. Subscribes to the probes' MQTT temperatures, runs a PID loop per heated vessel, and drives the SSRs with time-proportional output:

• HERMS channel — modulates the HLT element to hold the mash temperature (wort recirculating out of the HERMS coil), with an HLT over-temp cutout.
• Boil channel — drives the boil-kettle element to a setpoint.

The first two ULN2003A channels drive the SSRs; the other five are broken out for future use (pumps, alarm, …). It supports OTA updates over MQTT so we can iterate without touching the hardware. See boil_controller/README.md.

Temperature sensors

Each is an independent standalone probe publishing to MQTT. Planned points:

Probe device id	Measures	Used by the controller for
hlt	Hot Liquor Tank	HERMS over-temp cutout
herms_out	MLT output / mash temp off the HERMS coil	HERMS PID process variable
boil_kettle	Boil kettle	Boil PID process variable
(more)	e.g. mash-in, ambient	future channels / logging

Topic convention (shared prefix): mechination/<device_id>/temperature, with availability at mechination/<device_id>/status and a per-reading …/temperature/status that goes offline on an RTD fault (so the controller can fail-safe).

old/ — previous designs (reference only)

The earlier brewery was Bluetooth-based and is superseded by the WiFi/MQTT design above. Kept for reference:

• old/brewery-circuit/ — the original controller schematic + PCB (Brewery.kicad_pcb, KiCad/2019): ESP32-WROVER + ULN2003A + LTC2986. This is where the boil-controller pinout came from.
• old/ssr/ — BLE-central SSR firmware (an ESP-IDF BLE example, not the real app)
• old/hw/SSR/ — single-channel SSR PCB (PN2222A driver + opto) — still useful HW
• old/hw/Temp_probe/ — temp-probe PCB
• old/temp_sensor/ — MicroPython MAX31865 driver
• old/zephyr_temp/ — Zephyr RTOS temperature app
• old/web/ — the old Web-Bluetooth brewery dashboard

The old boil-controller firmware was not recovered (nothing referencing the LTC2986 exists under ~/dev, and the old system was Bluetooth-based), so boil_controller/ is a clean rebuild. The hardware schematic survives in old/brewery-circuit/, and the controller pinout is taken from it:

Function	GPIO
SSR — HERMS/HLT (ULN OUT3)	GPIO32
SSR — Boil (ULN OUT4)	GPIO33
Spare ULN outputs (OUT5–7)	GPIO25/26/27
LTC2986 SPI (unused)	MOSI 23, MISO 19, SCLK 18, CS 5, DRDY 4

⚠️ The board's first two ULN channels (DO1/DO2) land on GPIO34/35, which are input-only — they can't drive outputs, so the SSRs use the first output-capable channels (DO3/DO4 → OUT3/OUT4). The LTC2986 is dropped from the design (temps come over MQTT) but is held quiescent in firmware since it's still populated on the board. Details in boil_controller/README.md.

Building

Both firmwares are independent ESP-IDF projects (ESP-IDF ≥ 5.3; tested with the installed ~/esp/esp-idf). Build each from its own directory:

. ~/esp/esp-idf/export.sh

# Temperature probe (XIAO ESP32-C6)
cd stand_alone_temp_probe
idf.py set-target esp32c6
idf.py menuconfig          # WiFi, MQTT, device id, RTD type/pins
idf.py -p <PORT> flash monitor

# Boil controller (ESP32-WROVER)
cd ../boil_controller
idf.py set-target esp32
idf.py menuconfig          # WiFi, MQTT, sensor topics, ULN GPIOs, PID gains
idf.py -p <PORT> flash monitor

The two boards target different chips (esp32c6 vs esp32), so keep their build trees separate (each has its own sdkconfig). A convenience script is at tools/build.sh:

./tools/build.sh both        # build both
./tools/build.sh probe       # just the temp probe
./tools/build.sh boil flash  # build + flash the controller (auto-detects port)

After the controller's first USB flash, subsequent updates can go over the air — see boil_controller/README.md.