Flex Sensor in range 6K ~ 7K ohms reading with ADC

Other Hardware General Electronics
1

Hi. I'm playing with a flex sensor, wich is basically a variable resistor. In the range Im using it, it produces resistances between 6K (min) and 7K (max) ohms. I'm using another resistor of 4,7K and reading the flex sensor with Arduino ADC between the flex sensor and the resistor.
Problem is that i'm loosing lot of resolution using this approach, because the basic flex sensor resistance starts at 6K.
Wich is the best solution to compensate this, in order to get on the adc pin 0 ~ 5 volts with the variable resistor moving between 6K and 7K ohms?

Thanks very much
regards;
fernando

2

The typical method is to use a "resistance Bridge" (you can google this).

The issue that will have is the measurement must be made from two points where neither is a ground (of the arduino).

You could then read the bridge voltage with THIS

Or you could use the above ADC board with the circuit you have and get more resolution than the Arduino A/D

3

I would say you use a pull-up resistor to get the resolution you need. I'm not sure if 4.7kOhm is the right resistor for this. The value of the pull-up resistor will depend on your setup. I know it is a trial and error method, but you'll get good results.

4

I was just thinking that with only a 1µF capacitor to create an RC circuit, the time constant would vary from 6000µs to 7000µs, the difference being 1000µs. The analog comparator could be used to generate an interrupt that allows you to measure this time difference.

5

Using some OpAmps you can first offset the signal to one of the power rails, then amplify the voltage to reach the other rail.

Another option would indeed be a Wheatstone bridge.

6

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