Coffee machine control, in two connected boards

Countertop grind-and-drip appliances

A local start sequence, separate grinder and heating commands, and jug/water contacts form the control layer for an atmospheric-pressure drip-coffee appliance.

Office and shared pantry stations

An OLED presents machine and sensor information. The dedicated local STOP path remains available without a network connection, while water and jug inputs govern the active cycle.

Appliance product integration

Separate main and UI boards allow the display, keys and antenna to be placed away from the control circuits. Connector tables, harness definitions and STEP files support electrical and mechanical integration.

Engineering and service workbenches

Three low-voltage indicator loads, serial diagnostics and offline NTC calibration tools help inspect wiring, command sequences and sensor conversion using the same documented interfaces.

Main control board

STM32G030K6T6
127 × 85 mm · 2-layer FR-4, 1.6 mm

The STM32 owns the state machine, real ADC sampling, physical START/STOP, input interlocks, relay commands and watchdog. It runs the control loop independently of the display and Wi-Fi tasks.

Interface and Wi-Fi board

ESP32-C3-MINI-1-H4X
100 × 50 mm · 2-layer FR-4, 1.6 mm

The ESP32-C3 handles OLED pages, MENU/UP, buzzer indications, UART polling and physical-button Wi-Fi setup. START/STOP contacts pass through the board to the STM32 without connecting to ESP32 GPIO.

Temperature and calibration

ADC_IN0 measures the 10 kΩ NTC divider. The software checks open/short limits and sample age, then converts the ADC value with a lookup table. The download includes a 25°C/90°C offline calibration tool that accepts recorded ADC and reference temperatures and generates traceable conversion data without changing firmware or network settings.

Three water levels and jug presence

Water contacts close to ground at low, middle and high positions. Legal numeric masks are 0, 1, 3 and 7: empty, low, low+middle and all three. Empty water prevents start; inconsistent combinations latch a fault. Losing water or the jug during an active cycle switches off commands and latches the fault.

Protection-chain feedback

ADC_IN1 monitors V12_SAFE through a 47 kΩ / 10 kΩ divider. Opening the low-voltage NC protection chain removes relay-coil supply and latches a software fault; chain recovery does not restart the cycle. This chain does not remove DRV8871 motor power or open welded contacts, so final heat protection belongs in the separate load circuit.

Local stop and fault reset

STOP takes priority over START. With inputs safe, a new two-second local STOP hold clears a latched fault to idle; a further new START press is required. Holding START during power-up does not trigger a cycle. Invalid or stale samples and cycle time limits also turn commands off.

Power and sensing

Mean Well GST25A12-P1J 12 V supply; TDK dry NTC assembly; three RSF54Y100RC float switches; Littelfuse 59140-1-S-02-A reed sensor with 57140-000 magnet for jug presence.

Display and harnesses

The external 2.42-inch OLED uses a signal-mapped adapter harness. The package specifies board-to-board, sensor, protection-chain, display and programming wire connections with connector and terminal selections.

Mounting and 3D integration

The dry electronics enclosure is defined at 220×160×80 mm with separate main/UI mounts and an external OLED carrier. STEP, DXF and mounting drawings connect enclosure geometry to the boards’ mounting holes.

Programming and inspection tools

STLINK-V3MINIE with a STDC14-to-5-pin adapter serves MAIN; a 3.3 V USB-UART serves UI. The SIM3 enclosure provides three separate low-voltage indicator circuits. Serial CLI and calibration templates accompany the wiring and measurement guides.