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Software configurable Analog/Digital Input

Almerindo Paiva
Intellectual 410 points


I wounder if someone could help me.

I want to develop a universal data-acquisition board, that have eight inputs that can be individually software configured as 4-20mA, 0-10V, NTC, 12 or 24 Vdc digital input, or 12-24 Vdc high speed digital input(100Khz).

I know that high speed digital input will introduce noise in the system and, maybe this feature won't be implemented in the board.

What is the best configuration to do this, taking in account the on resistance of the analog switch, when one input is configured as 4-20mA or NTC.

I start with the following circuit, that is a single input interface. This circuit should be connected to an ADC with at least two differential inputs, one to measure the signal an the other to measure the voltage dropped over the ntc linearization resistor. But this solution will be expensive because it requires 5 switches per input + 8 ADC's.

Thanks for any suggestions,

Regards,

A. Paiva