Alternating analog readings in Arduino?

Hello,

I want to use Arduino for monitoring the electrical conductivity of a fluid at two different places in the same container. I follow this link, where the fluid acts as the second resistance of two voltage dividers. The problem is that because I am measuring at two places through e.g. A0 and A1, the electricity used for measuring A0 affects the readings of A1, and viceversa. So for measuring the correct fluid electrical conductivity at A0 I need to manually interrupt the 5V-A1-GND circuit. And that's quite far from my monitoring aims! And I do not want to use two arduinos.

Now I would like to ask you whether there's a way of interrupting and alternating the measurents of A0 and A1 automatically? I.e. a way of interrupting the 5V-A0-GND circuit and the 5V-A1-GND circuit automatically?

Cheers from the kingdom of Denmark

Need more info. Fluid resistance, pull up resistor values, layout, code.

Common ways to fix crosstalk between analogue inputs: 1) 100n capacitor from analogue input to ground, one for each input. 2) Two successive readings, and only use the last one. Leo..

ivino: a way of interrupting the 5V-A0-GND circuit and the 5V-A1-GND circuit

You could use 2 output pins to drive 2 PNP transistors to supply the 5V to your measurement points.

 +---EBC---------Rk--+------Ru--+
 |    |              |          |
 |    |              |          |
 +---------EBC---Rk------+--Ru--+
 |    |     |        |   |      |
 |    R     R        |   |      |
 |    |     |        |   |      |
 o    o     o        o   o      o
+5V   D0    D1       A0  A1    GND

(Rk = known resistance; Ru = unknown resistance you want to measure)

I.e. a way of interrupting the 5V-A0-GND circuit and the 5V-A1-GND circuit automatically?

If you connect the resistors not to the 5V but to a separate output pin, then when you want to measure A0 make A0’s resistor high, take the measurement and make A0’s resistor out of circuit by setting that output pin to be an input.
Do the same for the other analogue input.

Thanks a lot for your help! :.) I like all the options but I thinkn the one using the digital output is the most simple :-) I've tried by just setting the Digital Pin to low instead of changing it to input, and it works as well (In thi way I do not need to set as output at the beginning of the loop again).

I'm glad to be able to use Arduino for this project :-)

Cheers from the Kingdom of Denmark

/Ivan