# Synergy Logic SLM-RP4: Raspberry Pi 4 industrial controller with stackable I/O

> **Key takeaway:** Synergy Logic's $249 UL-listed SLM-RP4 industrial edge controller brings stackable I/O expansion up to 128 points to the Raspberry Pi 4 platform with preinstalled OpenPLC Runtime.

**Published:** 2026-10-22T03:04:11+00:00 
**Source:** LinuxGizmos 
**Category:** open-hardware 
**Canonical URL:** https://fosswire.org/news/synergy-logic-slm-rp4-raspberry-pi-4-industrial-controller-w.html 

## Summary
Synergy Logic has launched the SLM-RP4, a DIN rail-mounted industrial controller built on the Raspberry Pi 4 with Broadcom BCM2711, 2GB RAM, and 16GB storage. The device runs Raspberry Pi OS and ships with OpenPLC Runtime preinstalled for IEC 61131-3 PLC programming. Its key differentiator is an SPI-based backplane supporting up to eight stackable I/O modules, yielding up to 128 I/O points without separate communication cables. The controller is UL-listed and CE-marked for industrial use, with 18 module types available covering digital, relay, analog, and thermocouple I/O.

## I/O expansion and software options
- **Processor**: Broadcom BCM2711 with four 64-bit Arm Cortex-A72 cores, 2GB LPDDR4-3200, 16GB microSD storage
- **I/O backplane**: SPI-based, supports up to 8 stackable modules via integrated edge connectors on 35mm DIN rail
- **Module range**: 18 types including 16-channel digital inputs, 15-channel transistor outputs, 8/16-channel relays, 8-channel analog (0-10V/0-20mA or 4-20mA), and 4-channel thermocouple (SLM-THM-4) with 16-bit resolution
- **OpenPLC integration**: Preinstalled Runtime with hardware support package for I/O configuration; scan intervals configurable 1-1000ms (default 10ms); bus fault detection can halt PLC and zero outputs
- **Alternative programming**: Python or C++ libraries provided for direct backplane access without OpenPLC
- **Connectivity**: Gigabit Ethernet, dual-band 802.11ac Wi-Fi, Bluetooth 5.0/BLE, 2x USB 3.0, 2x USB 2.0, dual micro-HDMI, 3.5mm audio
- **Environmental**: Passive cooling, aluminum enclosure, 0°C to 50°C operating range, 24VDC Class 2 power input
- **Certifications**: UL 61010, UL 61010-2-201, CE EN 61131-2, EN 61010; Powered by Raspberry Pi approved

## Why it matters
The SLM-RP4 fills a gap between hobbyist Raspberry Pi projects and proprietary industrial PLCs by combining Pi 4 compute with certified hardware, modular I/O, and open-source OpenPLC software. The Python/C++ library option also enables custom edge applications beyond traditional PLC programming.