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MiniPLC

README.md

HomeMaster MiniPLC (ESP32)

HomeMaster MiniPLC

DIN rail • 24 V DC • ESP32 • Modbus RTU • Home Assistant

Overview

The HomeMaster MiniPLC is a professional, open-source DIN rail controller built around the ESP32 platform, designed for robust and scalable smart automation in residential, commercial, and light industrial environments. It combines industrial digital inputs, relay outputs, RS-485 communication, real-time clock functionality, and USB programming interface.

Engineered for reliability and flexibility, the MiniPLC supports 24 V DC industrial power input and features an integrated RS-485 Modbus interface for expansion with compatible industrial I/O modules and field devices. Its local processing capability ensures continued operation even when network or cloud connectivity is lost, making it suitable for mission-critical applications.

This controller operates as a complete standalone automation system using its onboard relay and digital input channels, while also offering seamless expansion via the RS-485 bus to connect additional industrial modules for automation, monitoring, and control. It provides a versatile, ready-to-integrate platform for HVAC control, energy management, security systems, lighting automation, and custom industrial applications.

Quick Overview

  • ESP32 industrial controller platform
  • Industrial DIN-rail form factor with 24 V DC supply
  • Runs locally and offline without cloud dependency
  • Expandable via RS-485 Modbus field devices

Typical Applications

  • Industrial automation controller
  • HVAC automation and plant control
  • Energy management systems
  • Industrial I/O controller
  • Building management systems (BMS)
  • SCADA edge controller
  • RS-485 Modbus master / field gateway

Tech Specs

Specification Details
Microcontroller ESP32-WROOM-32U (dual-core)
Power Input 24 V DC nominal (V+ / 0V) OR 85–265 V AC (L / N) OR 120–370 V DC (L / N + / −)
Digital Inputs 4 × isolated, 24 V DC compatible
Relay Outputs 6 × SPDT — 3 A MAX continuous per output (board/system limit).
Relay component contacts rated up to 12 A @ 250 V AC (resistive).
Analog Inputs 4 × 0–10 V, 16-bit (ADS1115)
Analog Output 1 × 0–10 V, 12-bit (MCP4725)
Temperature Inputs 2 × RTD (PT100/PT1000 via MAX31865), 2 × 1-Wire (DS18B20 compatible)
Display 128 × 64 OLED (SH1106)
User Interface 4 buttons, 3 user LEDs, 1 status LED, onboard buzzer (GPIO2, PWM)
Wi-Fi Wi-Fi (ESP32)
Ethernet Optional Ethernet (LAN8720 PHY)
RS-485 RS-485 Modbus RTU (MAX485, half-duplex) with TVS surge protection, PTC fuses, EMI choke, and fail-safe biasing
Storage MicroSD card (SPI interface, power-switched 3.3 V rail)
USB USB-C (ESD protected, CC detection, data to ESP32)
RTC PCF8563 with battery backup

Note: Relay outputs are not internally fused. Use external overcurrent protection per local code and use an external contactor/relay for loads above 3 A or with high inrush/inductive characteristics.

Installation, Environmental & Mechanical

Category Specification Details
Terminal Specifications Terminal type Pluggable screw terminal blocks, 5.08 mm pitch
Terminal pitch 5.08 mm
Wire cross-section 0.2–2.5 mm² (AWG 24–12)
Conductor type Solid or stranded copper
Stranded wire Ferrules recommended
Tightening torque 0.4 Nm (max)
Environmental Ratings Operating temperature 0 °C to +40 °C
Storage temperature -10 °C to 55 °C
Relative humidity 0–90 % RH, non-condensing
Ingress protection IP20 (inside cabinet)
Installation Indoor control cabinet only; not for outdoor or exposed installation
Terminal protection All wiring terminals must be protected against accidental contact
Mechanical & Packaging Product dimensions 157.4 × 91 × 58.4 mm
(6.2 × 3.58 × 2.3 in) (L × W × H)
DIN units 9 division units (≈ 90 mm DIN rail mounting width)
Mounting 35 mm DIN rail
Net weight 300 g
Gross weight 450 g
Pack size 230 × 140 × 87 mm (9 × 5.5 × 3.4 in) (L × W × H)
Mechanical drawing Front + side views with DIN-clip depth (see below)
Notes All dimensions shown in millimeters unless stated otherwise

Install only inside a control cabinet with ventilation; the cabinet must include a protective front plate covering all module connection terminals and a closing protective door; not for outdoor or exposed installation.

All wiring terminals must be protected against accidental contact by an insulating front plate, wiring duct, or terminal cover. Exposed live terminals are not permitted.

Mechanical Drawing

Mechanical drawing: front view + side view + DIN-clip depth (all dimensions in mm).

Home Assistant & ESPHome Integration

The MiniPLC comes with ESPHome pre-installed and can be integrated directly into Home Assistant without flashing custom firmware.

Quick Setup Process (Improv Wi-Fi)

  1. Mount & Power – Install on a 35mm DIN rail and connect power.
  2. Open Improv – Go to improv-wifi.com.
  3. Connect – Use USB-C (Serial) or Bluetooth LE.
  4. Enter Wi-Fi – Input SSID and password, then press Connect.
  5. Auto-Discovery – Device appears in Home Assistant & ESPHome Dashboard.

One-Click Import (ESPHome Dashboard)

Once connected to Wi-Fi, the MiniPLC is automatically discovered in the ESPHome Dashboard. Click "Take Control" to import the official configuration directly from GitHub.

USB Type-C Manual Flashing (Optional)

  1. Connect the MiniPLC to your computer using USB Type-C.
  2. Download the official YAML configuration: miniplc.yaml
  3. Open ESPHome Dashboard and import the YAML file.
  4. Update Wi-Fi credentials in the YAML.
  5. Flash directly from ESPHome (no reset or boot buttons required).
  6. The device reboots automatically and runs the new firmware.
  • No firmware flashing required for basic use
  • Native Home Assistant API
  • OTA updates supported
  • Automatic ESPHome dashboard import
  • Full YAML customization

Improv Setup

Documentation

The MiniPLC is open-source hardware. You can build your own board using the files below.

Hardware Design Files

File Description Link
Schematic (MCU Board) Main controller board schematic MCU_Board.pdf
Schematic (Relay Board) Relay and power section schematic Relay_Board.pdf
Schematic (USB Board) USB-C interface and power management USB_Board.pdf

Firmware & Software

Resource Description Link
Default ESPHome Config Pre-configured YAML for Home Assistant miniplc.yaml
Firmware Source Code Latest firmware builds and source Firmware/
ESPHome Integration Guide Complete setup instructions README.md

Manuals & Datasheets

Document Description Link
Datasheet Technical specifications and ratings Datasheet.pdf
User Manual Installation and configuration guide User_Manual.pdf

All design files and documentation are available in the HomeMaster GitHub repository.

Power Supply

⚠️ Hazardous voltage: Terminals L / N may carry mains AC or high-voltage DC. Wiring must be performed by qualified personnel. Disconnect power before wiring or servicing. Provide external overcurrent protection per local electrical code.

⚠️ Critical: Exactly ONE power input method may be used at a time. V+ / 0V and L / N must never be connected simultaneously.

MiniPLC supports one power input method at a time: 24 V DC nominal on V+ / 0V (recommended) or Mains AC / High-Voltage DC on L / N via the onboard isolated power module.

When to use which: 24 V DC is recommended when available, as it is safer and simpler to install. Mains AC / High-Voltage DC on L / N is for installations where 24 V DC is not available and must be installed by qualified personnel in accordance with local electrical codes.

⚠️ Safety reminder: When using L / N terminals for mains AC or high-voltage DC, ensure all power is disconnected before any wiring work. Installation and maintenance must be carried out by qualified personnel in accordance with local electrical codes, including proper overcurrent protection.

Power Input Specifications

Input Option Terminals Range Notes
24 V DC (recommended) V+ / 0V 24 V DC Preferred for most installations. Powers internal rail +24VDC_FUSED.
Mains AC L / N 85–265 V AC, 47–63 Hz Uses onboard isolated module to generate the internal 24 V rail. External protection required.
High-Voltage DC L / N (+ / −) 120–370 V DC Uses onboard isolated module to generate the internal 24 V rail. External protection required.

24 V DC Input (V+ / 0V)

24V DC Wiring
Connect + to V+ and − to 0V. 		Installation checklist
  • Use a regulated 24 V DC supply
  • Install 0.5 A fuse/breaker upstream of V+
  • Observe polarity: V+ / 0V
  • Route power wiring away from low-level analog signal wiring
  • Typical operating current: 150 mA @ 24 V (≈ 3.6 W) — measured typical device power consumption
  • Internal rail: 24 V input is conditioned into +24VDC_FUSED
  • Input protection: surge suppression (TVS), EMI filtering, reverse-polarity / power-path protection
  • Internal service fuse: 1.0 A (soldered) — service replacement required if blown
  • Upstream protection (recommended): external 0.5 A slow-blow fuse or 0.5 A breaker on V+ so the external device clears before the internal service fuse. Recommended for 24 V DC installations to protect wiring and simplify troubleshooting.

Mains AC / High-Voltage DC Input (L / N)

The onboard isolated power module generates the internal 24 V rail from 85–265 V AC or 120–370 V DC on L / N.

85–265 V AC (L / N)
Mains AC Wiring
  • Input: 85–265 V AC, 47–63 Hz
  • Qualified personnel only
  • External fuse/breaker required
 120–370 V DC (L / N + / −)
High-Voltage DC Wiring
  • Input: 120–370 V DC
  • Observe polarity where marked on L / N
  • External fuse/breaker required

⚠️ Mandatory upstream protection (L / N): Install an external T0.5 A (slow-blow) fuse or 0.5 A breaker upstream. Increase rating only if required by local code or to prevent nuisance trips due to inrush. External protection is required for mains AC / high-voltage DC installations due to safety regulations and the higher fault current available from these sources.

Onboard Isolated Power Module:

Parameter Specification
Type Isolated AC/DC power module
Input 85–265 V AC (47–63 Hz) or 120–370 V DC
Output 24 V DC auxiliary rail — maximum capacity 220 mA (power module rating, not typical device draw)
Protection Overcurrent, short-circuit, thermal shutdown with auto-recovery

Current draw clarification: The 150 mA figure is the typical operating current drawn by the MiniPLC device itself. The 220 mA figure is the maximum output capacity rating of the onboard isolated power module. Current is drawn by the load (the MiniPLC); the higher number represents the module's capacity limit, not additional current consumption.

Important: Use only one input method at a time: V+/0V or L/N.

Inputs & Outputs

Digital Inputs (4 channels)

Channel Pin Type Voltage Description
DI #1 GPIO36 Sourcing 24 V DC Isolated 24 V digital input with internal field supply, dry contact
DI #2 GPIO39 Sourcing 24 V DC Isolated 24 V digital input with internal field supply, dry contact
DI #3 GPIO34 Sourcing 24 V DC Isolated 24 V digital input with internal field supply, dry contact
DI #4 GPIO35 Sourcing 24 V DC Isolated 24 V digital input with internal field supply, dry contact

Features:

  • 4× isolated 24 V DC digital inputs using ISO1212 digital input receivers
  • Internal fused 24 V field supply for dry-contact sensing
  • Sourcing-type inputs for passive devices (relay contacts, open-collector outputs)
  • Separate field ground and logic ground domains
  • Per-channel protection with resettable PTC fuses and TVS surge suppression
  • Integrated EMI and noise filtering on each input
  • Configurable input inversion and debounce filtering via ESPHome
  • Status monitoring via Home Assistant binary sensors
Digital Input Wiring 1
Wiring example: dry contact wiring to DI inputs. 		Digital Input Wiring 2
Wiring example: shared common wiring approach.

Relay Outputs

The MiniPLC provides 6 SPDT mechanical relays (HF115F/005-1ZS3) for switching AC or DC loads. Each relay exposes NO / NC / COM contacts and is driven via optocoupler-isolated control circuitry.

System/board rating: 3 A MAX per output (system limit). The MiniPLC board/system can safely carry ONLY 3 A per relay output. Using more than 3 A directly can overheat and permanently damage the board.

Relay contact (component) rating: 12 A @ 250 V AC (resistive). This value belongs ONLY to the relay component itself and is NOT usable as a system output rating. The MiniPLC must NOT be used above 3 A.

Loads above 3 A (or inductive/inrush loads) MUST be switched using an external contactor or power relay. The MiniPLC relay may be used as a control signal for the external contactor. Do not attempt to switch loads above 3 A directly through the MiniPLC relay outputs.

⚠️ External protection required: Every relay output MUST be protected by an external fuse or circuit breaker (max 3 A per channel). Relay output circuits are not internally fused. External overcurrent protection is mandatory for safe operation.

Relay Specifications

Channel Control Pin Type Rating Description
Relay #1 PCF8574B:2 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 1 (NO/NC/COM)
Relay #2 PCF8574B:1 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 2 (NO/NC/COM)
Relay #3 PCF8574B:0 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 3 (NO/NC/COM)
Relay #4 PCF8574A:6 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 4 (NO/NC/COM)
Relay #5 PCF8574A:5 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 5 (NO/NC/COM)
Relay #6 PCF8574A:4 SPDT 12A @ 250V AC (relay component rating, NOT usable as system output)
3 A MAX per output (board/system limit)		 General purpose relay output 6 (NO/NC/COM)

Relay Wiring Examples

Relay Wiring
Example wiring using Normally Open (NO) and Normally Closed (NC) relay contacts.
  • Each relay has COM / NO / NC terminals
  • Use NO for default OFF loads
  • Use NC for default ON loads
  • ⚡ Loads may carry hazardous voltage
  • Supports AC and DC switching (DC and inductive loads require derating)

⚠️ External protection rule: Every relay output MUST be protected by an external fuse or circuit breaker. The rated current of the protective device shall not exceed 3 A MAX per output (board/system limit).

⚠️ Common protection warning: If a single common fuse or circuit breaker is used to protect multiple relay outputs (as shown in the wiring example), the protective device shall NOT be sized by summing relay outputs. The rating of the common protective device shall not exceed 3 A MAX per output (board/system limit).

For inductive or DC loads (contactors, solenoids, motors), use appropriate suppression (RC snubbers, MOVs, or flyback diodes). Loads exceeding the recommended PCB current limit shall be switched using external contactors or wiring methods that bypass PCB copper paths.

Analog I/O (0–10V)

MiniPLC provides 4 analog inputs and 1 analog output with a standard 0–10V signal range. Use these channels for common sensors, transmitters, and control devices that accept/produce 0–10V signals.

Analog Inputs (AI) — 4 Channels

Analog Input Specifications
Channel Signal Range Resolution Description
AI #1 0–10V 16-bit Analog input 1
AI #2 0–10V 16-bit Analog input 2
AI #3 0–10V 16-bit Analog input 3
AI #4 0–10V 16-bit Analog input 4
Analog Input Wiring
Analog Input Wiring
Example: multiple 0–10V sensors powered from a shared supply (PS) with common 0V/GND. 		Wiring Checklist (AI)
  • Signal: 0–10V
  • Reference: connect sensor 0V to AI GND
  • Use a shared 0V/common ground between sensors and MiniPLC
  • For long runs, use a twisted pair (Signal + GND)
  • Keep analog wiring away from relay outputs and mains/AC wiring

Analog Output (AO) — 1 Channel

Analog Output Specifications
Channel Signal Range Resolution Description
AO #1 0–10V 12-bit (4096 steps) Analog output for control signals
Analog Output Wiring
Analog Output Wiring
Example: 0–10V analog output connection to an external device. 		Wiring Checklist (AO)
  • Signal: 0–10V
  • Reference ground: AO GND
  • Use a twisted pair (AO + AO GND) for long runs
  • Keep AO wiring away from power switching and motor/VFD cables
Typical use cases: analog setpoints (VFD speed), valve/actuator positioning, controller reference signals.

Temperature Inputs

MiniPLC supports RTD sensors (PT100/PT1000) and 1-Wire temperature sensors (DS18B20 or compatible) for reliable cabinet and process temperature monitoring.

Temperature Input Specifications

Type Channel Sensor / Interface Range Accuracy
RTD RTD #1 PT100/PT1000 (SPI front-end) -200°C to +850°C ±0.5°C typical
RTD RTD #2 PT100/PT1000 (SPI front-end) -200°C to +850°C ±0.5°C typical
1-Wire BUS #1 DS18B20 (or compatible) -55°C to +125°C ±0.5°C
1-Wire BUS #2 DS18B20 (or compatible) -55°C to +125°C ±0.5°C

Wiring Examples

1-Wire Wiring
1-Wire wiring example. 		RTD 4-Wire Wiring
RTD wiring example (4-wire).
RTD 2-Wire Wiring
RTD wiring example (2-wire). 		RTD 3-Wire Wiring
RTD wiring example (3-wire).

User Interface

Component Quantity Control Description
Front Panel Buttons 4 PCF8574A:0-3 Tactile buttons for local control
User LEDs 3 PCF8574A:4-6 Configurable indicator LEDs
Status LED 1 PCF8574A:7 System status indicator
OLED Display 1 I²C (0x3C) 128×64 pixel SH1106 display
Buzzer 1 GPIO2 Audible alarm/notification

Features:

  • Buttons can be mapped to toggle relays, trigger scenes, or custom actions
  • LEDs can show relay status, system state, or custom patterns
  • OLED displays time, sensor readings, and system status
  • Buzzer provides audible feedback for alarms or notifications

Communication & Protocols

  • Modbus RTU (RS-485) – UART-based communication for expansion modules and field devices
  • Wi-Fi – ESP32 integrated (Improv onboarding supported)
  • Ethernet – Optional via LAN8720 PHY

RS-485 Communication (Modbus RTU)

The MiniPLC provides a half-duplex RS-485 interface with integrated protection and fail-safe biasing. The interface is available on the A / B / COM terminals.

Hardware Features:

  • RS-485 transceiver: MAX485 (half-duplex)
  • Fail-safe biasing network on A/B (idle state defined)
  • Common-mode choke for EMI suppression
  • TVS surge and ESD protection on A/B/COM
  • Resettable PTC fuses on A and B lines
  • Bidirectional logic level shifting between MCU and transceiver

RS-485 Wiring

RS-485 Wiring 1
Connect A, B, and COM to the bus. 		RS-485 Wiring 2
Add 120Ω termination only at the two physical ends of the bus.

Termination & Biasing

  • Terminate with 120 Ω only at the two ends of the line.
  • Do not terminate intermediate devices.
  • Fail-safe biasing is already provided inside the MiniPLC.

COM / Reference Ground

  • Connect COM between all RS-485 nodes.
  • This limits common-mode voltage and prevents communication faults.

Power Supply for Extension Modules

  • Recommended: Use the same power supply for MiniPLC and all RS-485 extension modules.
  • Distribute power in a star topology from the PSU.
  • If separate PSUs are used, connect 0V references together at one point (unless the extension module is galvanically isolated).

A common 0V reference prevents RS-485 common-mode voltage errors and communication faults.

Tip: Cable recommendations, shield bonding, and routing rules are defined in the Cable Recommendations & Shield Grounding section below.

Cable Recommendations & Shield Grounding

This section applies to Analog (0–10V), Temperature (RTD / 1-Wire), and RS-485. Use shielded, twisted constructions and bond shields correctly to reduce EMI and ground-loop issues.

General Routing Rules

  • Route low-level signal cables (Analog/RTD/1-Wire/RS-485) separately from mains, relay outputs, contactors, VFD motor cables, and power wiring.
  • If crossing power cables is unavoidable, cross at 90°.
  • Keep cable runs as short as practical and avoid parallel runs with high-current conductors.

Analog (0–10V) Cable

  • Construction: twisted pair (Signal + GND) per channel
  • Shielding: overall shield (standard) or individually shielded pairs (high-EMI)
  • Examples: J-Y(ST)Y (overall shield) or LI2YCY PIMF (shielded twisted pairs; one pair per channel)

Temperature Cable

RTD (PT100/PT1000):

  • Recommended: shielded multi-core for 2/3-wire; shielded pairs for best accuracy (4-wire)
  • Examples: J-Y(ST)Y (overall shield) or LI2YCY PIMF (pairs; e.g. 2×2×0.50 for 4-wire)

1-Wire (DS18B20):

  • Recommended: shielded 3-core ( +5V / DATA / GND ) for typical installations
  • High-EMI / long runs: shielded pairs + overall shield (e.g. LI2YCY PIMF 2×2×0.50)
  • Topology: daisy-chain (bus). Avoid star wiring.
  • Stubs: keep sensor stubs ≤ 0.5 m.
  • Pull-up (DATA): 4.7 kΩ typical; 2.2–3.3 kΩ for long/heavy loads.

RS-485 Cable

  • Construction: twisted pair for A/B
  • Characteristic impedance: 120 Ω (recommended)
  • Shielding: overall shield is recommended in cabinets; use individually shielded pairs + overall shield in high-EMI
  • Examples: J-Y(ST)Y 2×2×0.5 mm² or LI2YCY PiMF 2×2×0.50
  • Use one twisted pair for A/B. Use the second pair for COM (0V reference) or spare.

Shield Grounding

  • Default recommendation: bond cable shield(s) to cabinet PE/EMC ground at the PLC end only.
  • Do not connect shields to signal terminals (AI/AO/RTD/1-Wire/RS-485 A/B/COM).
  • If both ends are in equipotential bonded cabinets, shields may be bonded at both ends using proper 360° clamps.

System Architecture & Pinout

System Block Diagram
System block diagram showing internal architecture and interfaces. 		Pinout Diagram
Complete GPIO and connector pin assignments.

ESPHome YAML Configuration & Hardware Pinout Manual

Introduction

The HomeMaster MiniPLC has ESPHome preinstalled, and the behavior is defined by the miniplc.yaml configuration file. This file contains all hardware definitions, sensor configurations, and I/O mappings for the device.

The default configuration can be downloaded from GitHub:

The default configuration includes all essential components enabled, while optional features such as Ethernet, RTD temperature sensors, 1-Wire sensors, microSD card, and web server are commented out. To enable any optional feature, remove the # comment markers from the beginning of the relevant configuration block and adjust parameters as needed for your specific installation.

ESP32 GPIO Pinout (MiniPLC)

GPIO Net Name Function Used By
GPIO36 DI24V-1 Digital Input 1 24V DI #1
GPIO39 DI24V-2 Digital Input 2 24V DI #2
GPIO34 DI24V-3 Digital Input 3 24V DI #3
GPIO35 DI24V-4 Digital Input 4 24V DI #4
GPIO32 ESP_SDA I²C SDA OLED, RTC, ADC, DAC, PCF8574
GPIO33 ESP_SDL I²C SCL OLED, RTC, ADC, DAC, PCF8574
GPIO17 TXD_RS0 UART TX RS-485
GPIO16 RXD_RS0 UART RX RS-485
GPIO5 1-WIRE1 1-Wire Bus #1 DS18B20
GPIO4 1-WIRE2 1-Wire Bus #2 DS18B20
GPIO2 BUZZER PWM Output Buzzer
GPIO12 MISO SPI MISO SD / RTD
GPIO13 MOSI SPI MOSI SD / RTD
GPIO14 SCLK SPI Clock SD / RTD
GPIO15 SD_CS SPI CS microSD
GPIO23 ETH_MDC RMII MDC Ethernet PHY
GPIO18 ETH_MDIO RMII MDIO Ethernet PHY
GPIO19 ETH_TXD0 RMII TXD0 Ethernet PHY
GPIO22 ETH_TXD1 RMII TXD1 Ethernet PHY
GPIO21 ETH_TXEN RMII TXEN Ethernet PHY
GPIO26 ETH_RXD0 RMII RXD0 Ethernet PHY
GPIO25 ETH_RXD1 RMII RXD1 Ethernet PHY
GPIO27 ETH_CRS_DV RMII CRS_DV Ethernet PHY
GPIO0 ETH_CLK RMII 50 MHz REF Ethernet Clock
GPIO1 CS_RTD1 SPI CS MAX31865 #1
GPIO3 CS_RTD2 SPI CS MAX31865 #2

PCF8574 Mapping

PCF8574A (0x38)

Pin Signal Function
P0 BTN1 Button 1
P1 BTN2 Button 2
P2 BTN3 Button 3
P3 BTN4 Button 4
P4 LED1 User LED 1
P5 LED2 User LED 2
P6 LED3 User LED 3
P7 LED_STATUS Status LED

PCF8574B (0x39)

Pin Relay
P0 Relay 3
P1 Relay 2
P2 Relay 1
P4 Relay 6
P5 Relay 5
P6 Relay 4

ADS1115 Analog Inputs

Channel Terminal ESPHome Name
A0 AI0 Analog Input 1
A1 AI1 Analog Input 2
A2 AI2 Analog Input 3
A3 AI3 Analog Input 4

WiFi

Wi‑Fi credentials by default YAML config are set via Improv (Serial/BLE) and do not require changes to the YAML.
If you need to force static Wi‑Fi configuration instead of Improv, you can manually edit the wifi: block in miniplc.yaml (SSID, password, static IP, gateway, subnet, DNS).

Ethernet

Enable when you want to use Ethernet instead of Wi‑Fi. The ESPHome stack and ESP32‑WROOM do not support using Wi‑Fi and Ethernet at the same time. To use Ethernet, you must comment out the wifi: block that is normally configured via Improv (Serial/BLE) and uncomment the ethernet: block in miniplc.yaml.

The Ethernet block uses fixed hardware pins as defined in the MiniPLC schematics: GPIO23 for MDC, GPIO18 for MDIO, GPIO0 for the 50 MHz RMII reference clock, and PHY address 1. These pins and clk_mode are part of the MiniPLC hardware design and must not be changed.

ethernet:
  type: LAN8720
  mdc_pin: GPIO23
  mdio_pin: GPIO18
  clk_mode: GPIO0_OUT
  phy_addr: 1

I²C

The I²C bus is used by the OLED display, RTC (PCF8563), ADC (ADS1115), DAC (MCP4725), and PCF8574 I/O expanders.
It is enabled by default and required for most MiniPLC functionality.
Change frequency to adjust I²C speed (default 400 kHz). Modify timeout for bus timeout. Set scan: true to scan for devices on boot.

MiniPLC I²C Address Map

Device I²C Address YAML ID / Usage Function
OLED (SH1106 128×64) 0x3C display: Status screen
RTC (PCF8563) 0x51 time: Real-time clock
ADC (ADS1115) 0x48 ads1115: 4× analog inputs (AI0–AI3)
IO Expander A (PCF8574) 0x38 pcf8574_hub_a Buttons + LEDs
IO Expander B (PCF8574) 0x39 pcf8574_hub_b Relays
DAC (MCP4725) 0x60 output: 0–10 V analog output (AO) 
i2c:
  - id: bus_a
    sda: 32
    scl: 33
    frequency: 400kHz
    timeout: 1s
    scan: true

RS-485 UART & Modbus

The MiniPLC exposes a half‑duplex RS‑485 bus on the A/B/COM terminals, driven by the ESP32 UART on GPIO17 (TX) and GPIO16 (RX).
This bus is used for Modbus RTU communication with external expansion modules such as DIO‑430‑R1, DIM‑420‑R1, and ENM‑223‑R1.

  • The uart: block configures the physical RS‑485 port (GPIO pins, baud rate, parity, stop bits).
  • The modbus: block defines a shared Modbus bus instance that all extension modules attach to via modbus_controller: or packages:.

You normally only change the baud_rate (default 19200) and, if required, parity/stop_bits to match your Modbus network.
The TX/RX pins are fixed by hardware and must remain GPIO17/16.
Each extension module must have a unique Modbus address set in its own WebConfig (DIP/menu) and referenced in the YAML.

Base RS‑485 + Modbus bus configuration:

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200
  parity: NONE
  stop_bits: 1

modbus:
  id: modbus_bus
  uart_id: uart_modbus
Example: DIO‑430‑R1 Digital I/O Module

Minimal controller-side YAML on the MiniPLC to talk to one DIO‑430‑R1 using the official package:

uart:
  id: uart_modbus
  tx_pin: 17
  rx_pin: 16
  baud_rate: 19200
  parity: NONE
  stop_bits: 1

modbus:
  id: modbus_bus
  uart_id: uart_modbus

packages:
  dio1:
    url: https://github.com/isystemsautomation/HOMEMASTER
    ref: main
    files:
      - path: DIO-430-R1/Firmware/default_dio_430_r1_plc/default_dio_430_r1_plc.yaml
        vars:
          dio_prefix: "DIO#1"   # Shown in Home Assistant entity names
          dio_id: dio_1         # Internal unique ID in ESPHome
          dio_address: 4        # Modbus address set in the DIO WebConfig
    refresh: 1d

For multiple DIO‑430‑R1 units, duplicate the dio1: block (dio2:, dio3:, …) with unique dio_id, dio_prefix, and dio_address values.

Note: Detailed instructions for wiring, Modbus addressing, and YAML options for each expansion module (DIO‑430‑R1, DIM‑420‑R1, ENM‑223‑R1, ALM‑173‑R1, etc.) are provided in their respective README.md files in the HOMEMASTER repository. Always refer to the module‑specific README for coil/register maps, entities, and recommended settings.

1-Wire

The MiniPLC provides two independent 1-Wire buses for DS18B20 temperature sensors. The hardware pinout is fixed: Bus #1 uses GPIO5, Bus #2 uses GPIO4. These pins cannot be changed as they are defined by the PCB design.

To use 1-Wire sensors, uncomment the sensor blocks in the YAML and configure the sensor addresses. You can adjust update_interval and customize sensor name values, but the GPIO pins are hardware-defined.

one_wire:
  - platform: gpio
    pin: GPIO05
    id: hub_1
  - platform: gpio
    pin: GPIO04
    id: hub_2

# Example sensor configuration:
sensor:
  - platform: dallas_temp
    one_wire_id: hub_1
    address: 0x0000000000000000  # Replace with actual sensor address
    name: "1-WIRE Dallas temperature BUS1"
    update_interval: 60s
  - platform: dallas_temp
    one_wire_id: hub_2
    address: 0x0000000000000000  # Replace with actual sensor address
    name: "1-WIRE Dallas temperature BUS2"
    update_interval: 60s

SPI

The MiniPLC SPI bus is used by the microSD card and MAX31865 RTD temperature sensors. The hardware pinout is fixed: GPIO12 (MISO), GPIO13 (MOSI), GPIO14 (SCLK). These pins cannot be changed as they are defined by the PCB design.

To use SPI devices (microSD or RTD sensors), uncomment the spi: block. The pin assignments are hardware-defined and must match the PCB layout.

spi:
  miso_pin: GPIO12
  mosi_pin: GPIO13
  clk_pin: GPIO14

Digital Inputs

The MiniPLC provides four 24V isolated digital inputs (DI #1 through DI #4). The hardware pinout is fixed: GPIO36 (DI #1), GPIO39 (DI #2), GPIO34 (DI #3), GPIO35 (DI #4). These pins cannot be changed as they are defined by the PCB design.

You can reconfigure the name values for Home Assistant, add inverted: true if input logic needs inversion, and adjust filters for debouncing or signal processing. The GPIO pin assignments are hardware-defined.

binary_sensor:
  - platform: gpio
    pin:
      number: GPIO36
    name: "DI #1"
    # Optional: Add filters for debouncing
    # filters:
    #   - delayed_on: 50ms
    #   - delayed_off: 50ms
  - platform: gpio
    pin:
      number: GPIO39
    name: "DI #2"
  - platform: gpio
    pin:
      number: GPIO34
    name: "DI #3"
  - platform: gpio
    pin:
      number: GPIO35
    name: "DI #4"

Relays

The MiniPLC provides six SPDT relay outputs controlled via PCF8574B and PCF8574A I/O expanders. The hardware pinout is fixed: Relay #1 (PCF8574B:2), Relay #2 (PCF8574B:1), Relay #3 (PCF8574B:0), Relay #4 (PCF8574A:6), Relay #5 (PCF8574A:5), Relay #6 (PCF8574A:4). These PCF8574 pin assignments cannot be changed as they are defined by the PCB design.

You can reconfigure the name values for Home Assistant. The inverted: true setting is required for correct relay operation and must not be changed. The PCF8574 pin numbers are hardware-defined.

switch:
  - platform: gpio
    name: "RELAY #1"
    pin:
      pcf8574: pcf8574_hub_b
      number: 2
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "RELAY #2"
    pin:
      pcf8574: pcf8574_hub_b
      number: 1
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "RELAY #3"
    pin:
      pcf8574: pcf8574_hub_b
      number: 0
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "RELAY #4"
    pin:
      pcf8574: pcf8574_hub_a
      number: 6
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "RELAY #5"
    pin:
      pcf8574: pcf8574_hub_a
      number: 5
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "RELAY #6"
    pin:
      pcf8574: pcf8574_hub_a
      number: 4
      mode:
        output: true
      inverted: true

Buttons

The MiniPLC provides four front panel buttons connected to PCF8574A pins P0-P3. The hardware pinout is fixed: Button #1 (P0), Button #2 (P1), Button #3 (P2), Button #4 (P3). These PCF8574 pin assignments cannot be changed as they are defined by the PCB design.

You can reconfigure the name values for Home Assistant. The inverted: true setting is required due to the button pull-up configuration and must not be changed. You can add on_press or on_release actions to trigger automations. The PCF8574 pin numbers are hardware-defined.

binary_sensor:
  - platform: gpio
    name: "Button #1"
    pin:
      pcf8574: pcf8574_hub_a
      number: 0
      inverted: true
    # Optional: Add actions
    # on_press:
    #   - switch.toggle: relay_1
  - platform: gpio
    name: "Button #2"
    pin:
      pcf8574: pcf8574_hub_a
      number: 1
      inverted: true
  - platform: gpio
    name: "Button #3"
    pin:
      pcf8574: pcf8574_hub_a
      number: 2
      inverted: true
  - platform: gpio
    name: "Button #4"
    pin:
      pcf8574: pcf8574_hub_a
      number: 3
      inverted: true

LEDs

The MiniPLC provides three user LEDs (LED #1, #2, #3) and one status LED connected to PCF8574A pins P4-P7. The hardware pinout is fixed: LED #1 (P4), LED #2 (P5), LED #3 (P6), Status LED (P7). These PCF8574 pin assignments cannot be changed as they are defined by the PCB design.

You can reconfigure the name values for Home Assistant. The inverted: true setting is required for correct LED operation and must not be changed. The PCF8574 pin numbers are hardware-defined.

switch:
  - platform: gpio
    name: "LED #1"
    pin:
      pcf8574: pcf8574_hub_a
      number: 4
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "LED #2"
    pin:
      pcf8574: pcf8574_hub_a
      number: 5
      mode:
        output: true
      inverted: true
  - platform: gpio
    name: "LED #3"
    pin:
      pcf8574: pcf8574_hub_a
      number: 6
      mode:
        output: true
      inverted: true

status_led:
  pin:
    pcf8574: pcf8574_hub_a
    number: 7
    mode:
      output: true
    inverted: false

RTC

The MiniPLC includes a PCF8563 real-time clock at I²C address 0x51. The I²C address is fixed by the PCB design and cannot be changed.

You can modify synchronization settings in the homeassistant time platform block to adjust how the RTC syncs with Home Assistant time.

time:
  - platform: pcf8563
    id: pcf8563_time
    address: 0x51
  - platform: homeassistant
    on_time_sync:
      then:
        pcf8563.write_time:

OLED

The MiniPLC includes a SH1106 128×64 OLED display at I²C address 0x3C. The I²C address is fixed by the PCB design and cannot be changed.

You can reconfigure rotation to change display orientation (0, 90, 180, 270), adjust contrast percentage, and customize the lambda function to change displayed content. The I²C address is hardware-defined.

display:
  - platform: ssd1306_i2c
    model: "SH1106 128x64"
    address: 0x3C
    rotation: 180
    contrast: 100%
    id: oled_display
    update_interval: 1s
    lambda: |-
      it.printf(64, 0, id(font1), TextAlign::TOP_CENTER, "HOMEMASTER");
      it.strftime(0, 60, id(font2), TextAlign::BASELINE_LEFT, "%H:%M", id(pcf8563_time).now());

ADC (Analog Inputs)

The MiniPLC includes an ADS1115 16-bit I²C ADC at address 0x48 for reading four single-ended 0–10 V analog inputs.

Each channel is hardware conditioned by an LM224 op-amp buffer and resistor divider that scales the external 0–10 V signal into the ADS1115 input range.

Channel mapping (fixed by PCB)

ADS1115 Channel Internal Net Terminal
AIN0 AI0_ADC AI0
AIN1 AI1_ADC AI1
AIN2 AI2_ADC AI2
AIN3 AI3_ADC AI3

This mapping is hardwired on the PCB and cannot be changed in software.

Signal path (hardware)

External 0–10 V input →
resistor divider (47 kΩ / 47 kΩ network) →
LM224 buffer →
Schottky input clamps →
ADS1115 AINx

(see schematic, page 2, "ADC")

ESPHome configuration

ads1115:
  - address: 0x48
    id: adc_hub

sensor:
  - platform: ads1115
    ads1115_id: adc_hub
    multiplexer: A0_GND
    gain: 1
    name: "AI0"
    filters:
      - multiply: 0.00305

  - platform: ads1115
    ads1115_id: adc_hub
    multiplexer: A1_GND
    gain: 1
    name: "AI1"
    filters:
      - multiply: 0.00305

  - platform: ads1115
    ads1115_id: adc_hub
    multiplexer: A2_GND
    gain: 1
    name: "AI2"
    filters:
      - multiply: 0.00305

  - platform: ads1115
    ads1115_id: adc_hub
    multiplexer: A3_GND
    gain: 1
    name: "AI3"
    filters:
      - multiply: 0.00305

What can be configured in YAML

Parameter Purpose
multiplexer Selects AIN0–AIN3
gain Input range (must match hardware scaling)
filters.multiply Converts raw ADC value to volts
update_interval Sampling rate

What cannot be changed

  • I²C address (0x48)
  • Channel-to-terminal mapping
  • Input range (0–10 V)
  • Analog front-end scaling

These are fixed by the PCB design.

DAC

The MiniPLC includes an MCP4725 12-bit I²C DAC at address 0x60 for generating a single 0–10 V analog output (AO).

The DAC output is hardware conditioned by an LM224 op-amp stage and resistor scaling network that converts the MCP4725's 0–3.3 V output range into a field-level 0–10 V signal.

The I²C address (0x60) and output channel are fixed by the PCB design and cannot be changed in software.

Signal path (hardware):
MCP4725 DAC → RC filter → LM224 amplifier → scaling network → AO terminal

ESPHome configuration:

output:
  - platform: mcp4725
    id: dac_output

The DAC is exposed in ESPHome as a 0.0–1.0 normalized analog output.

Example (0–10 V control):

fan:
  - platform: speed
    output: dac_output
    name: "DAC 0–10V"
    speed_count: 100
Fan speed Output voltage
0% 0 V
50% ~5 V
100% ~10 V

Configurable in YAML: speed_count, automations, output.set_level
Fixed by hardware: I²C address, output range, scaling

Buzzer

The MiniPLC includes a buzzer connected to GPIO2 as a PWM output for audible notifications and alarms. The GPIO pin is fixed by the PCB design and cannot be changed.

You can reconfigure the frequency in the switch action to change tone, modify level percentage to change volume, and add multiple switch actions for different tones. The GPIO pin assignment is hardware-defined.

output:
  - platform: ledc
    pin: GPIO02
    id: buzzer_output

switch:
  - platform: template
    name: "Switch buzzer"
    optimistic: true
    turn_on_action:
      - output.turn_on: buzzer_output
      - output.ledc.set_frequency:
          id: buzzer_output
          frequency: "2441Hz"
      - output.set_level:
          id: buzzer_output
          level: "75%"
    turn_off_action:
      - output.turn_off: buzzer_output

RTD Inputs (RTD1 & RTD2)

The MiniPLC includes two MAX31865 RTD interface ICs for direct connection of PT100 and PT1000 sensors in 2-, 3-, or 4-wire configurations.

Each RTD channel has an on-board 8-position DIP switch block
(SW1 = RTD1, SW2 = RTD2) that configures the complete RTD bias, sense, and compensation network.

Every switch position is functional.
There is no unused or "default OFF" position — the entire 8-switch pattern must match the selected sensor type and wiring mode.

Factory DIP switch configuration (all 8 positions)

RTD1 → PT100, 2-wire

Switch 1 2 3 4 5 6 7 8
State ON ON OFF OFF ON ON OFF ON

RTD2 → PT1000, 2-wire

Switch 1 2 3 4 5 6 7 8
State ON OFF ON OFF ON OFF ON ON

DIP switch logic (per channel)

Switch 1 2 3 4 5 6 7 8
PT100 – ON OFF – – ON OFF –
PT1000 – OFF ON – – OFF ON –
2-wire ON – – OFF ON – – ON
3-wire OFF – – ON OFF – – ON
4-wire OFF – – OFF ON – – OFF

RTD DIP Switch Configuration


RTD DIP switch blocks (RTD1 and RTD2) on the MiniPLC PCB with silkscreened configuration table.

Terminal mapping (fixed by PCB)

Terminal Signal
1 FORCE+
2 RTDIN+
3 RTDIN−
4 FORCE−

ESPHome YAML configuration

spi:
  miso_pin: GPIO12
  mosi_pin: GPIO13
  clk_pin: GPIO14

sensor:
  - platform: max31865
    name: "RTD1 Temperature"
    cs_pin: GPIO1
    rtd_nominal_resistance: 100
    reference_resistance: 400
    wires: 2

  - platform: max31865
    name: "RTD2 Temperature"
    cs_pin: GPIO3
    rtd_nominal_resistance: 1000
    reference_resistance: 400
    wires: 2

How to change sensor type or wiring

  1. Power OFF the MiniPLC
  2. Set all 8 DIP positions according to the table above
  3. Update YAML (rtd_nominal_resistance and wires)
  4. Power ON and verify temperature

Fixed by hardware

  • MAX31865 IC
  • SPI pins and CS pins
  • Reference resistor network
  • Terminal order

Configurable in YAML

  • Sensor type (PT100 / PT1000)
  • Wiring mode (2/3/4 wire)
  • Update interval and filtering
  • Alarm thresholds

Links