Electronic – arduino – Set up an array of pressure sensors

adcarduinosensorvoltage divider

I am working with a flexiforce pressure sensor 25 lb.

I have to run 6 of them in parallel and I'm using an Arduino Uno. I'm not an electrical engineer (read: I'm a computer science major) and this is a school project. I am using a voltage divider for a single flexiforce to test the range and I don't know what the best fixed resistor value to use in order to get a larger range.

I am currently using a 200 Ohm resistor and am getting range from 0 to 30 (full range is to 1233)

Here is there recommended circuit:

enter image description here

Using the Arduino, I can't make the amplifier thing or have a negative voltage input. Can someone please explain a way to get 6 of these sensors in an array with the highest sensitivity? Can I use a 9 V battery as an amplifier?

Best Answer

In this answer I showed that the optimal series resistor value is

\$ R_S = \sqrt{R_{MIN} \cdot R_{MAX}} \$

where \$R_{MIN}\$ and \$R_{MAX}\$ are the minimum and maximum resistances of your sensor. The Sparkfun page speaks of between infinity and 300 kΩ. If we assume 10 MΩ as maximum value then your series resistor should be 1.8 MΩ (rounded to nearest E12 value).

These are pretty high values, too high for an ADC, which, like Mathieu says, likes a impedance of less than 10 kΩ. So you'll need to buffer the divider with an unity gain buffer opamp:

enter image description here

Note that a common opamp may have an input bias current as high as 1 µA, and this could distort your reading. A CMOS opamp like the MCP600x has a much lower input bias current, 1 pA typical for the MCP600x, which won't deteriorate your reading.

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