Industrial Grad Custom PLC Design & Development

# Custom Industrial PLC Hardware & Firmware Development

We are looking for an experienced **Embedded Systems / Industrial Electronics Engineer** to design and develop a custom industrial PLC/controller suitable for real industrial environments.

The objective is to develop a reliable, professional, manufacturable controller based on a custom PCB, not a hobby-level Arduino or development-board solution.

The engineer should have strong experience in industrial electronics, embedded firmware, PCB design, EMC/ESD protection, industrial communications, and microcontroller-based control systems.

## Project Objective

Develop a compact industrial PLC/controller capable of handling digital and analog I/O, industrial communications, machine-control logic, and optional IoT connectivity.

The controller should be designed for reliable operation in industrial environments where electrical noise, motors, contactors, VFDs, and other sources of interference may exist.

We are currently considering architectures based on:

- STM32 or another suitable industrial-grade MCU
- ESP32-S3 or similar device for IoT/wireless connectivity

However, this architecture is only a proposal.

We expect the selected engineer to review the requirements and recommend the best architecture based on reliability, cost, manufacturability, performance, and future scalability.

## Proposed Initial Hardware Requirements

Target input power:

- 24 VDC industrial supply

Proposed I/O:

- 8 × 24 VDC Digital Inputs
- 8 × protected 24 VDC Digital Outputs
- 4 × Analog Inputs
- 2 × Analog Outputs

Preferred analog support:

- 0–10 V
- 4–20 mA

Communication interfaces may include:

- Ethernet
- RS-485 / Modbus RTU
- Modbus TCP
- CAN or CAN-FD
- USB-C service/programming port
- Wi-Fi
- Bluetooth/BLE

Additional features may include:

- RTC
- Non-volatile memory
- Hardware watchdog
- Diagnostics
- Status LEDs
- Expansion interface for future I/O modules

## Firmware Requirements

For the initial version, we do not necessarily require CODESYS, OpenPLC, or a graphical Ladder programming environment.

The main controller can be programmed directly using C/C++.

The firmware should provide a clean and reusable control framework supporting functions such as:

- Digital inputs and outputs
- AND / OR / NOT logic
- Set/Reset and latching
- TON / TOF timers
- Counters
- Analog scaling
- PID control
- Interlocks
- Alarm handling
- Modbus communications
- System diagnostics

FreeRTOS or another RTOS may be used if recommended by the engineer.

The control logic should remain fully operational independently of internet, cloud, or wireless connectivity.

## Optional IoT Architecture

We are also considering a separate IoT communication processor such as ESP32-S3.

Possible IoT functions include:

- Wi-Fi
- BLE provisioning
- MQTT
- HTTPS/API communication
- Cloud monitoring
- Alarm/event reporting
- Machine status reporting
- Remote diagnostics
- OTA firmware updates
- Future mobile/web application integration

The IoT processor must not interfere with or compromise the reliability of the main machine-control functions.

The engineer should advise whether:

1. A dual-MCU architecture is preferable, or
2. A single MCU can reliably handle all required functions.

## Industrial Design Requirements

The final product must be designed for industrial environments.

The engineer should have experience with:

- Input/output isolation
- Surge protection
- ESD protection
- EFT/transient protection
- Reverse polarity protection
- Overvoltage protection
- Overcurrent/short-circuit protection
- EMI/EMC filtering
- Grounding strategy
- Isolation strategy
- Industrial power-supply design
- Proper PCB creepage and clearance
- Noise-resistant PCB layout

The design should take future compliance with relevant industrial standards into consideration, particularly PLC/industrial control and EMC requirements.

Formal certification is not necessarily part of the first prototype, but the hardware should be designed with future certification in mind.

## Mechanical Requirements

The controller is expected to use a compact industrial enclosure suitable for DIN-rail mounting.

The engineer should advise whether:

- CPU and I/O should be on one PCB, or
- CPU and I/O should use separate modular boards.

Future expansion modules should also be considered during the architecture stage.

## Expected Deliverables

The selected engineer should be capable of delivering:

1. System architecture
2. Detailed block diagram
3. Component selection
4. Complete schematic
5. PCB layout
6. Gerber files
7. Manufacturing files
8. BOM with manufacturer part numbers
9. Firmware source code
10. Programming/debugging instructions
11. Prototype bring-up support
12. Hardware testing procedure
13. Firmware testing procedure
14. Design documentation
15. Recommendations for future certification
16. Support during prototype manufacturing and debugging

All editable source files must be provided at the end of the project.

## Required Experience

Please apply only if you have strong experience in several of the following areas:

- Industrial electronics
- PLC hardware development
- Embedded systems
- STM32
- ESP32
- C/C++
- FreeRTOS
- Industrial I/O design
- 24 VDC digital inputs/outputs
- 0–10 V and 4–20 mA interfaces
- Modbus RTU
- Modbus TCP
- RS-485
- Ethernet
- CAN/CAN-FD
- EMC/ESD protection
- Industrial PCB design
- Power electronics
- Hardware debugging
- Prototype development

Previous experience designing industrial controllers, PLCs, remote I/O modules, motor controllers, industrial gateways, or similar products is highly preferred.

## When Applying

Please provide:

- Examples of similar industrial products you have designed
- Your role in those projects
- MCU/platform used
- PCB design experience
- Firmware development experience
- Experience with industrial EMC/ESD protection
- Proposed architecture for this project
- Recommended MCU(s)
- Whether you recommend single-MCU or dual-MCU architecture
- Estimated development time
- Estimated engineering cost
- Estimated prototype cost if applicable
- Number of PCB prototype iterations you expect
- Tools used for schematic and PCB design
- Firmware development environment

Please also explain any changes you would recommend to the proposed specifications.

We are looking for an engineer who can provide a **production-oriented industrial design**, not only a working prototype.

The final design should balance:

**Reliability + Industrial Performance + Manufacturability + Reasonable Cost + Reasonable Development Time.**