I want to measure the voltage of several batteries while using the Arduino for controlling some relais and running the energy monitor software.
Now I’m asking myself how many pins are left unused after mounting the emonTx-shield on the baseplate.
I just read this in another forum:
“Shift registers are only one option you can use chips called port expanders connected either through the I2C or SPI buses on the arduino.
Typical of these would be the MCP23S17 and the MCP23017 - each give you 16 more input / output pins and you can connect eight easily and more with a it of trickery.”
(by Grumpy_Mike, how to add more digital pins to Arduino Uno ?! [SOLVED] - Project Guidance - Arduino Forum)
So are those I2C or SPI buses still free to use with the emonTx shield?
I read on the arduino-tutorial-site that by “Using a parallel to serial shift register you can collect information from 8 or more switches while only using 3 of the pins on your Arduino.”. Which is also a good option.
Are there some obivous and important pros and cons for either way?