--- title: "vscp-demo-pico-fridge-ctrl" url: "https://maker.wiznet.io/Grace_Koo/projects/vscp-demo-pico-fridge-ctrl/" markdown_url: "https://maker.wiznet.io/Grace_Koo/projects/vscp-demo-pico-fridge-ctrl/md" type: "UCC: User Created Content" author: "grodansparadis" author_url: "https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl" editor: "WIZnet" editor_url: "https://maker.wiznet.io/" original_author: "grodansparadis" original_url: "https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl" published: "2026-04-06" language: "en" hardware: ["WIZnet W55RP20-EVB-Pico"] likes: 0 views: 321 comments: 0 source: "WIZnet Makers (https://maker.wiznet.io/)" --- # vscp-demo-pico-fridge-ctrl > A W55RP20-EVB-PICO monitors fridge temperature via NTC thermistor, controls a compressor relay, and publishes VSCP events to MQTT over Ethernet. Original author: grodansparadis (source: https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl) ## Components - **WIZnet W55RP20-EVB-Pico** x 1 ([docs](https://wiznet.io/products/powered-by-raspberry-pi/w55rp20-evb-pico)) ## Article ## VSCP Fridge Controller on the W55RP20-EVB-PICO A network-connected fridge temperature controller — built on WIZnet's **W55RP20-EVB-PICO**. An NTC thermistor measures fridge temperature in real time. The controller turns the compressor on or off based on a configurable setpoint. Temperature readings and alarms are automatically published to an MQTT broker, so the fridge can be monitored and configured remotely without touching the hardware. The communication layer uses **VSCP (Very Simple Control Protocol)**, an open IoT automation framework. The project was developed by Åke Hedman (grodansparadis), who is also the creator of VSCP itself. --- ### 1. Background: What Is VSCP? ![](https://maker.wiznet.io/upload/ckeditor5/425649697%5F1776076713%2Epng) ** **VSCP (Very Simple Control Protocol)** is an open, free IoT/M2M automation framework designed for resource-constrained devices. VSCP is an application-level protocol that uses CAN, RS-232, Ethernet, TCP/IP, MQTT, or other transport mechanisms, and works over both cable and wireless connections. Key characteristics relevant to this project: - **Event-driven** — nodes publish typed events (temperature readings, alarms) rather than raw data - **Standardized event classes and types** — e.g., class=10/type=6 for temperature, class=1/type=2 for alarms - **Register-based configuration** — each node exposes a register map for reading/writing configuration over the network - **GUID-based addressing** — each node has a globally unique 16-byte identifier, derived here from the W55RP20's MAC address - **Transport-agnostic** — this project uses MQTT as the transport layer (VSCP Level II) --- ### 2. Project Overview The firmware implements a closed-loop temperature controller with the following behavior: - Reads temperature from an NTC thermistor using the **Steinhart–Hart equation** - Compares current temperature against a configurable setpoint with hysteresis - Controls a compressor relay (on/off) - Publishes temperature readings periodically to an MQTT broker as VSCP events - Publishes alarm events when temperature exceeds high or low thresholds - Exposes a register map for remote configuration via MQTT subscribe **Hardware:** | Component | Role | | --- | --- | | WIZnet W55RP20-EVB-PICO | Main controller — RP2040 MCU + W5500 Ethernet | | NTC thermistor | Temperature measurement | | Compressor relay | Cooling control output | | KiCad schematic | Custom interface board (included in repo) | --- ### 3. System Architecture ![](https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl/raw/main/images/IMG_20241028_211113.jpg) *https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl* ```plaintext [NTC Thermistor] │ ADC ▼ [W55RP20-EVB-PICO] RP2040 — reads ADC, applies Steinhart-Hart equation W5500 — hardware TCP/IP, handles Ethernet │ │ MQTT over TCP ▼ [MQTT Broker] │ ├── publish: /vscp/GUID/1040/6/# (temperature events) └── publish: /vscp/GUID/1/2/# (alarm events) │ └── subscribe: /vscp/GUID (register read/write commands) ``` --- ### 4. VSCP Event Mapping VSCP defines standardized event classes and types. This project uses: | Event | VSCP Class | VSCP Type | MQTT Topic Pattern | | --- | --- | --- | --- | | Temperature reading | 1040 (Measurement float) | 6 (Temperature) | `/vscp/GUID/1040/6/#` | | Alarm | 1 (Alarm) | 2 (Alarm) | `/vscp/GUID/1/2/#` | The GUID is derived from the W5500 MAC address (default: `FF:FF:FF:FF:FF:FF:FF:FE:00:08:DC:12:34:56:00:01`), making each device addressable by its hardware identity on the MQTT broker. --- ### 5. WIZnet's Role: W55RP20 as the Network-Connected Controller The W55RP20 integrates the RP2040 MCU and W5500 Ethernet controller in a single SiP package. The W5500's hardwired TCP/IP stack handles the MQTT TCP connection and packet processing independently of the RP2040, which focuses on the control logic — ADC readings, Steinhart–Hart calculations, setpoint comparisons, and VSCP event construction. The project uses WIZnet's **WIZnet-PICO-C** library (included as a submodule) for W5500 Ethernet driver support on the RP2040/pico-sdk stack. --- ### 6. Project Info | | | | --- | --- | | **Author** | Åke Hedman (grodansparadis) | | **Repository** | [github.com/grodansparadis/vscp-demo-pico-fridge-ctrl](https://github.com/grodansparadis/vscp-demo-pico-fridge-ctrl) | | **License** | MIT | | **WIZnet hardware** | W55RP20-EVB-PICO | | **Protocol** | VSCP Level II over MQTT | | **Language** | C (84%), CMake (16%) | | **MDF** | [eurosource.se/w55rp20_frc01.xml](https://www.eurosource.se/w55rp20_frc01.xml) | - VSCP GitHub : - W55RP20 VSCP Fridge Controller : --- Source: https://maker.wiznet.io/Grace_Koo/projects/vscp-demo-pico-fridge-ctrl/