I'm brainstorming right now, working on ideas for adding an analog input signal on an espresso machine. Assume the setup is nearly worst case scenario - 60Hz mains hum vulnerability, inductive noise spikes from motors and solenoids starting and stopping, reasonable, but still imperfect grounding schemes, etc. The only bright spot is that wire runs are not terribly long, probably 8-10' on the longest runs. There are 240VAC lines running and switching all over the place, and the sensors are running on a 5VDC supply.
In this scenario, if you had a 5VDC sensor board that needed to send a signal to the main control board MCU, which system would you use, and why?
1) Simple analog 0-5VDC
a) what sorts of input/output impedances?
2) Current loop 4-20mA
3) Frequency (V-F and F-V converters)
4) PWM
5) Digital I2C, SPI, or RS485, including ADC in sensor board
6) Other options I've not considered.
In this scenario, if you had a 5VDC sensor board that needed to send a signal to the main control board MCU, which system would you use, and why?
1) Simple analog 0-5VDC
a) what sorts of input/output impedances?
2) Current loop 4-20mA
3) Frequency (V-F and F-V converters)
4) PWM
5) Digital I2C, SPI, or RS485, including ADC in sensor board
6) Other options I've not considered.