I have a project where I need to monitor the state of 5 DPDT electrical switches with Arduino Uno. Also, the Arduino board will be measuring the output from 3 thermocouples on 3 of the analogue pins as input and sending signals to open and close 3 relays for heaters on the 3 of the digital pins as output. The data with the state of the microswitches and the measurements from the thermocouples will be send over a serial connection to a PC.
I think I need a shield with at least 20 inputs for monitoring the 5 DPDT electrical switches (5 x 2 x 2). The common of the switches will be connected to a common rail. Can I use an I2C extension shield for this purpose? Is this going to create an issue with the serial connection? Any specific shield recommendations?