We designed and developed a control system that uses our new board with Android operating system and a 7″ capacitive touch screen (figure on the right). It is connected to a pool of Arduino’s slaves over rs485 channel. Our tests suggest that the most efficient and lightweight communication protocol is the modbus. It works greatly also on Arduino devices. Indeed, we used Maxim’s max485 chip in order to convert Arduino TTL serial signal to rs485. Terminator resistor (120 Ohm) is connected accross the two wires to limit data corruption.
In the picture on the left, we sketched an overview schema of the system together with the possible communication channels that our Android touch screen is able to handle.
From the software point of view, an Android app will represent the master of the system. To communicate with the slaves, it uses a native modbus library that we wrote and tested specifically for these systems. The system could be expanded using other channels such as rs232, i2c and Ethernet.
For the details of the electronic parts, Arduino souce code, circuit diagram, etc we suggest you to read this blog post.