Why OEMs Are Moving Away from Traditional PLCs
Traditional PLCs were designed as general-purpose industrial controllers — highly flexible but expensive when deployed at scale. When you're building hundreds of identical machines per year, you're paying for features you don't need: programming environment licenses, modular expansion capability, and brand margins that can represent 40–60% of the module cost.
A custom industrial control board strips away the unnecessary layers. It delivers exactly the I/O count, communication protocols, and processing power your application requires — nothing more, nothing less. The result: lower BOM cost, smaller cabinet footprint, and full control over your product's hardware platform.
Step 1: Map Your Current PLC Architecture
Start by documenting your existing PLC setup in detail:
- I/O map: Count and classify all digital inputs/outputs, analog channels, and special-function modules (counters, PWM, encoder inputs)
- Communication protocols: Identify fieldbus connections (EtherCAT, CANopen, Modbus RTU/TCP, PROFINET), HMI interfaces, and uplink protocols to MES/SCADA
- Control cycle requirements: Document your fastest scan cycle — 1ms, 5ms, or 10ms? This determines the MCU performance tier needed
- Program complexity: Estimate the ladder logic or structured text size, number of function blocks, and any PID/motion control tasks
Step 2: Select the Right Board Platform
Based on your I/O and performance requirements, select a board platform. Here's a quick decision framework:
| Requirement | Recommended Platform | Typical Use Case |
|---|---|---|
| Cost-sensitive, basic logic | STM32F103ZE | HMI, sensor integration, basic control |
| Standard PLC replacement | STM32F407 | Machine controller, gateway, DTU |
| High-performance computing | STM32H743 | Vision, DSP, precision control |
| Real-time Ethernet | EtherCAT F429 | Servo drives, distributed I/O, robotics |
For a detailed comparison, see our STM32 Industrial Control Board Selection Guide.
Step 3: Firmware Adaptation
This is the most critical phase. Your PLC ladder logic or structured text needs to be translated into embedded firmware (typically C/C++ running on FreeRTOS or bare-metal):
- Control logic translation: Convert PLC function blocks into C functions with deterministic timing
- Communication stack: Implement the required protocol drivers (EtherCAT slave, Modbus RTU, CAN, etc.)
- Safety and watchdog: Implement hardware watchdog, fault detection, and safe-state management
- OTA update capability: Build in firmware update mechanism for field maintenance
Step 4: Pilot Validation
Before committing to volume production, run a pilot validation phase:
- Install board-based controller in 1–3 machines alongside the existing PLC version
- Run parallel testing for 2–4 weeks, comparing output accuracy and reliability metrics
- Validate communication timing, I/O response, and edge-case behavior
- Collect field data and iterate on firmware if needed
Step 5: Scale to Production
Once pilot validation passes, transition to volume production:
- Finalize PCB layout and order production batch
- Set up board-level testing fixtures for quality control
- Establish firmware release management and version control
- Phase out PLC procurement gradually over 1–2 production cycles
Cost Impact Analysis
For a typical packaging machine using a Siemens S7-1200 configuration (CPU + 2 signal modules + communication module), switching to an STM32F407 industrial board can reduce controller hardware cost from ~$1,800 to ~$990 per machine — a 45% saving. At 200 machines/year, that's $162,000 annual hardware savings.
Use our Cost Estimation Calculator to model savings for your specific configuration.