Made for ESPHome
Listed under Made for ESPHome — officially recognised by the ESPHome project, not merely compatible.
Runs without the server
The controller thinks, the home server displays. Logic programmed into the MiniPLC runs on the controller itself, independent of the server and the network.
One device, not three
6 relays, 0–10 V in and out, PT100/PT1000 inputs and a 24 V DC or 85–265 V AC input — no extra I/O board, no separate power supply.
Open hardware
Schematics and PCB files under CERN-OHL-W v2, firmware under MIT. You own the design, not a vendor.
MiniPLC · ESP32 DIN-rail controller
The controller runs the plant. Home Assistant is the dashboard.
Relays, 0–10 V, PT100/PT1000 and a Modbus RTU master in one 9-module housing. Logic written in ESPHome runs on the device.
ESP32 DIN-rail controller for Home Assistant
Made for ESPHome · Home Assistant via the ESPHome API · Modbus RTU master · Wi-Fi or Ethernet
HomeMaster MiniPLC is an ESP32 DIN-rail controller with industrial-grade protection on every channel, built for Home Assistant installations that live in a cabinet, not on a desk. In one 9-module mini-PLC housing it combines 6 SPDT relays, 4 isolated 24 V digital inputs, 4 × 0–10 V analog inputs (16-bit), a 0–10 V output (12-bit), two PT100/PT1000 RTD inputs, two 1-Wire buses and an RS-485 Modbus RTU master.
It connects over Wi-Fi or its built-in Ethernet port and runs ESPHome, so every input and output appears in Home Assistant as a ready entity — no MQTT broker, no Modbus register mapping. Think of it as a mini PLC for home automation: the control logic runs on the device, Home Assistant is the dashboard.
Home Assistant is the main platform, not the only one: with MQTT enabled in ESPHome, the MiniPLC also works with openHAB, ioBroker, Node-RED and SCADA systems.
If you have been looking for an Ethernet relay board for Home Assistant — ESP32, relays, DIN rail and ESPHome in one housing — this is it, with the analog, temperature and bus interfaces a heating or ventilation node needs on top.
Inputs and outputs at a glance
6 relay outputs
SPDT (NO / C / NC), 3 A at 250 V AC per contact. Pumps, valves, boiler demand, lighting circuits; heavier loads through a contactor.
4 isolated 24 V digital inputs
Dry contacts wetted by the module: wall switches, flow and level switches, alarm contacts.
0–10 V analog I/O in ESPHome
4 × 16-bit inputs for CO₂, humidity, pressure and soil-moisture transmitters, 1 × 12-bit output for EC fans, mixing valves and dampers.
PT100 / PT1000 inputs for Home Assistant
2 RTD channels for flow, return, tank and collector temperature, 2-, 3- or 4-wire, set per channel with a jumper block. Enabled in ESPHome when needed.
1-Wire for DS18B20 sensors
Two buses for room and pipe temperature, with no extra module.
RS-485 Modbus RTU master
Read energy meters, inverters and heat pumps, and run HomeMaster expansion modules on the same bus.
What problems it solves
No cloud, no manufacturer account
Nothing leaves your network. The MiniPLC talks to Home Assistant locally over the ESPHome API — no vendor cloud, no account, no subscription.
No vendor lock-in
Standard Modbus RTU on the bus, ESPHome on the controller, open schematics and firmware. You can repair it from the published schematics and reflash it with open firmware — the design is yours, not a vendor's.
No licences, no certified installer
No configuration software to buy, no licence per project and no certified-installer scheme. Configuration is ESPHome, free and open; any qualified electrician can wire the cabinet.
Expandable, not obsolete in five years
Start with the controller alone, add relays, dimmers, energy metering or leak detection over RS-485 when the house needs them. Nothing has to be replaced to grow.
Local logic, independent of the home server
Automations written into the MiniPLC run on the controller itself. The home server shows the state and changes settings.
Switch to light
A wall switch on a digital input switches a relay on the controller itself.
Pump follows temperature
PT100, PT1000 or 1-Wire readings drive a pump or a valve without a round trip.
Relays hold their state
If the network or the home server is unavailable, outputs stay where they are.
Modbus keeps polling
Expansion modules and meters on RS-485 are still read and written.
Display and buttons
128 × 64 OLED and 4 buttons for status and local actions in the cabinet.
After a reboot of the controller itself, relays start open.
Built for the cabinet, not the workbench
A dev board can switch a relay. The MiniPLC is built with industrial-grade protection on every channel, so it can be connected to 230 V and signed off in a panel.
Relays run far below their contact rating, so contacts do not burn; heavier and inductive loads go through a contactor, as in any professional panel.
CE-marked, EMC tested at an external laboratory.
EMI filter and X2 capacitor
On the mains L / N input.
Varistors and fuses
Surge and fault protection on the mains input.
Optocoupler-isolated relay drive
Logic kept apart from the relay coils.
Varistor on every contact
Relays run far below their rating: 3 A per output, contactor above.
TVS on digital inputs
Surge suppression on all 4 isolated inputs.
Resettable fuse per input
Plus reverse-polarity protection and an EMI filter per channel.
RS-485: 3× TVS, 2× PTC
A–COM, B–COM, A–B; 1.5 A PTC on A and B.
Common-mode choke
Surge protection on the bus, not galvanic isolation.
MiniPLC or MicroPLC?
Same ESP32, same ESPHome firmware. The difference is what sits on board.
MiniPLC
Controller with plant I/O on board
- Relays
- 6 × SPDT
- Inputs
- 4 digital, 2 × PT100/PT1000, 2 × 1-Wire
- Analog I/O
- 4 × 0–10 V in, 1 × 0–10 V out
- Power
- 24 V DC or 85–265 V AC
- Network
- Wi-Fi or Ethernet
- Width
- 9 DIN modules
MicroPLC
Head of the Modbus bus, compact
- Relays
- 1 × C / NC (fail-safe)
- Inputs
- 1 digital, 1-Wire
- Analog I/O
- —
- Power
- 24 V DC
- Network
- Wi-Fi
- Width
- 2 DIN modules
Choose the MiniPLC when relays, analog and temperature inputs belong in one housing; choose the MicroPLC when the I/O lives in modules or Modbus devices and the controller only has to run the bus.
What you can build with a MiniPLC
One controller, many jobs. Loads above 3 A per relay are switched through a contactor.
Boiler room and hydronic heating
Pumps and boiler demand on the relays, a 0–10 V mixing valve, PT100 on flow and return, 1-Wire sensors in the rooms — no expansion modules needed.
Ventilation and heat recovery with 0–10 V
Drive EC fan speed from the 0–10 V output, read CO₂ and humidity transmitters on the 0–10 V inputs, switch the bypass damper and heater stages on the relays.
Greenhouse, irrigation and garden
Soil-moisture sensors on 0–10 V, irrigation valves and vent motors on the relays, air temperature on 1-Wire, a rain or level contact on a digital input.
Solar thermal and buffer tank
PT1000 on the collector and the tank, the solar pump on a relay, a backup heater through a contactor — differential control running locally.
Pool and technical room
Water temperature on PT100, filter pump and heater through contactors, a flow switch on a digital input.
Wired whole-house controller
Wall switches on the inputs, lighting circuits through contactors, and HomeMaster expansion modules on RS-485 for more relays, dimmers, LED and alarm inputs.
Energy management and load control
Read a Modbus energy meter, shed a water heater through a contactor, signal a heat pump over a dry contact — or talk to it directly over Modbus RTU.
Modbus RTU gateway for Home Assistant
Bring RS-485 Modbus RTU meters, inverters and heat pumps into Home Assistant over Wi-Fi or Ethernet.
Modbus RTU master for expansion modules
The MiniPLC is the bus master for HomeMaster expansion modules — relays and inputs (DIO-430), AC dimming (DIM-420), LED control (RGB-621), alarm inputs (ALM-173), analog I/O and RTD (AIO-422), leak detection (WLD-521) and energy metering (ENM-223). Each module sits on the same RS-485 daisy chain and appears in Home Assistant through the controller.
Need 16 relays or more? Plan the panel in the System Builder.
Set up in two steps — no flashing
ESPHome is pre-installed. Connect the MiniPLC to Wi-Fi with Improv, over USB-C or Bluetooth, from a browser. Home Assistant discovers it automatically — click Add and every input and output is there.
Want to change the logic? Within 15 minutes of power-on, click Take control in the ESPHome Dashboard and save the device key it creates — you need it to move the device to another Home Assistant.
Power: 24 V DC or mains
Power the MiniPLC from 24 V DC on V+/0V (recommended) or from 85–265 V AC on L/N through the onboard isolated supply. Use one input at a time. Typical consumption is 150 mA at 24 V (about 3.6 W).
Technical specifications
| Microcontroller | ESP32-WROOM-32U-N16, dual-core |
|---|---|
| Relay outputs | 6 × SPDT (NO / C / NC), 3 A @ 250 V AC per output (module limit) |
| Digital inputs | 4 × isolated 24 V DC, dry contact, wetted by the module |
| 0–10 V analog inputs | 4 × 16-bit |
| 0–10 V analog output | 1 × 12-bit |
| PT100 / PT1000 RTD inputs | 2 × (2-, 3- or 4-wire) |
| 1-Wire | 2 buses, DS18B20 compatible |
| RS-485 | Modbus RTU master, half-duplex, surge-protected, not galvanically isolated |
| Network | Wi-Fi with external SMA antenna, or built-in 10/100 Ethernet used instead of Wi-Fi |
| Power input | 24 V DC, or 85–265 V AC 47–63 Hz; one at a time |
| Display and controls | 128 × 64 OLED, 4 buttons, 16 status LEDs, buzzer |
| Storage and service | microSD, USB-C |
| Dimensions | 158 × 90.6 × 67.3 mm, 9 DIN modules, 35 mm rail |
| Environment | 0 … +40 °C, 0–90 % RH non-condensing, IP20, indoor control cabinet |
| Warranty | 24 months |
Datasheet DS-MiniPLC Rev. B · 2026-09 · Hardware V1.0
What it is not
- Not for loads above 3 A per relay — use a contactor.
- Not for outdoor or unheated cabinets: 0 … +40 °C, IP20.
- RS-485 is surge-protected, not galvanically isolated — fit an isolator where the bus crosses into another installation.
- RTD inputs and Ethernet are disabled in the factory firmware and enabled in ESPHome when needed.
- The real-time clock has no battery fitted; time is synced from the home server or over SNTP.
- No proprietary configuration tool — logic is written in ESPHome (YAML) and Home Assistant.
Documents and downloads
| Datasheet | MiniPLC_Datasheet.pdf |
|---|---|
| User manual | User Manual.pdf |
| EU Declaration of Conformity | DoC_MiniPLC.pdf |
| UK PSTI statement | PSTI_MiniPLC.pdf |
| ESPHome configuration | miniplc.yaml |
| Schematics | Schematics/ |
| Full technical reference | README.md |
Wiring and installation
Wiring diagrams for every input and output, the terminal map, RTD configuration, cable and shield-grounding rules and the pinout are in the technical README:
Build guides
CE: EMC 2014/30/EU (EN 55032 Class B, EN 55035, tested at Idvorsky Laboratories), LVD 2014/35/EU (EN 62368-1), RED 2014/53/EU, RoHS 2011/65/EU. HomeMaster® is a registered EU trademark (EUTM 019082911). Hardware under CERN-OHL-W v2, firmware under MIT.
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