The Siemens S7-200 SMART ST40 is a step up from the ST30, offering more I/O capacity for complex automation projects. It features 24 digital inputs and 16 transistor outputs, making it suitable for mid-sized machines requiring multiple sensing and control points. Operating at 24 VDC, the ST40 supports transistor outputs, allowing fast response in digital switching tasks such as actuating solenoids, relays, and indicators.

The PLC includes both RS-485 and PROFINET Ethernet communication interfaces for integration with HMIs, drives, and SCADA systems. It comes with ~30 KB program memory and high-speed instruction execution suitable for time-sensitive logic. Expansion through signal boards is supported for analog processing or communication needs. The ST40 is frequently deployed in machinery automation, labeling systems, and motion-based applications requiring up to five axes of pulse output. It provides a good balance of performance and flexibility in compact installations.