Siemens CPU1215C input expansion and remote monitoring with Arduino bridge

Programmable Logic Controllers (PLC) are widely used in industrial to run an automated system. PLC must have some means of receiving and interpreting signal from another device such as sensors and switches. There are two main type of PLC input, discrete and analog. Arduino was built as a bridge or interface adding the capabilities of Siemens PLC CPU1215C to receive another type of input. In this study, Arduino is used to connect PLC with SHT11 sensor which has two wire serial communication. SHT11 temperature, humidity and dew-point data are read by Arduino and transmitted to PLC through LAN network provided by an Ethernet shield. The data can be send to MySQL server and displayed into PHP web page as monitoring screen. Using Arduino Mega 2560 and Wiznet W5100 Ethernet shield, single SHT11 data acquisition and monitoring needs 100 msec to read sensor value, 360 msec to connect and write data to PLC and 4.12 sec to connect and save data to database server, overall it needs 4.58 sec. The entire runtime determine the cycle period and it helps assign this Arduino bridge for the right application. The runtime obatined is feasible for non time critical application.