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Condition +-.1v from 2 wires to 0-5 for Arduino analog

by zsawyer
Tags: analog, arduino, condition, wires
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zsawyer
#1
Nov11-12, 03:16 PM
P: 5
I am toying around with connecting a 236PC 15GW pressure sensor to my arduino board.

I am supplying nearly 10 volts to the Sensor and can get +- .1V readings from some simple tests.

How do I condition these two lines that give +- .1V to range from 0-5 Volts for the Arduino analog pins.
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gnurf
#2
Nov11-12, 04:44 PM
P: 330
Quote Quote by zsawyer View Post
I am supplying nearly 10 volts to the Sensor and can get +- .1V readings from some simple tests. How do I condition these two lines that give +- .1V to range from 0-5 Volts for the Arduino analog pins.
You sensor signal needs to go through a two step process; amplification (K) and level shifting (B). The output of that process should be

K × Vin(min) + B = 0
K × Vin(max) + B = 5V

The min/max values are your sensor output, so your left with the trivial task of solving this linear system for K and B.

Do you know of a circuit or device that can amplify and/or level shift a signal?
zsawyer
#3
Nov11-12, 06:30 PM
P: 5
Thanks for the quick reply.

I think I should use an operational amplifier.

I was able to connect a General Operational Amplifier to 5volt+ and ground and got was able show a loss of voltage when negative pressure was given to the sensor. It clipped, I believe, when I tried giving the sensor a positive pressure. Purely from the Amp Voltage source, the gain was around 50 I believe. I tried cutting the supply by half, but thats below the OpAmps minimum Voltage. The operational Amplifier needs a gain of 25 but I cant have the Voltage below 5 V.

What I am figuring out is that I don't know how to do that with the two output wires from the Sensor that give both positive and negative voltages. Any help on good sources to learn from, or some documented example schematics would be helpful.

Microchip has an excellent document, but I am unsure of the reasoning for the diagram for the instrumentation amplifier on page 4. I am hesitant to put resistors on such a small voltage from my sensor and am unsure if the NTE975 chip is good for that schematic and what my Vdd should be.

I will try the schematic later this week, its getting late for me now. Any input or resources to clarify some of these concepts would be greatly appreciated. Thanks!

gnurf
#4
Nov12-12, 05:01 PM
P: 330
Condition +-.1v from 2 wires to 0-5 for Arduino analog

The level shift can be done by AC coupling your sensor signal into the output of a voltage divider. Then do the amplification. I'm speaking in general terms here—I haven't look at your sensor spec.
zsawyer
#5
Nov12-12, 11:52 PM
P: 5
My quest has now been to understand coupling and Why AC coupling.

In my search I found a wonderful article from the MIT media lab.
http://resenv.media.mit.edu/classes/MAS836/bias.pdf.

my initial thoughts are for DC coupling, I am trying to measure the pressure and dont expect any appreciable frequencies, which AC coupling for some reason makes me think of.

Page 8 of the document talks about differential Amplifier AC and DC, the only difference seems to be caps for filtering out frequencies, which I dont think is my case. getting alte again, Ill post when I have some success


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