Arduino IS.AB20REL.HF ARDBOX Relay 20 I/Os PLC Industrial Shields Arduino IS.AB20REL.HF ARDBOX Relay 20 I/Os PLC offers 20x digital inputs/outputs and provides a master-slave connection using I2C as communication between two computers. Programming through the USB is supported through Arduino LEONARDO. This feature allows the IS.AB20REL.HF ARDBOX relay PLC immediate access to the program, maintain and prepare it for set up, permitting users control of equipment without limits.