So, with the aim to adapt application voltage and/or current and provide as well the right galvanic isolation to the PLC, it is recommended to install per I/O the right interface providing both voltage-current level adaptation and isolation protection. Here I'll introduce programmable logic controller (PLC) input circuits using opto-couplers. I'll also discuss the concepts of SOURCE and SINK. 1 illustrates. I am in the process of designing a custom ATMega328P-based PCB (5V) that needs to receive and send discrete digital signals to a PLC (24V). I will be communicating with this DL05 PLC from automation direct: https://cdn. pdf I am using EL817 (c) optocouplers:. Since a PLC typically operates at extra-low voltage, a transformer is employed to reduce the mains voltage to a suitable value, and consequently these surges in voltages are transferred through the transformer to the processor. Isolation is used to manage ground potential differences. The input signal is interpreted as a logic high or low using a voltage comparator. Opto-isolation provides electrical separation using light, protecting sensitive control electronics from high-voltage field devices. It mitigates risks associated with electrical noise, voltage spikes, and wiring mistakes that can damage PLC components. Unlike transformers or capacitors, which can only transfer AC signals across the isolation barrier, optocouplers can.
