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varies upto 90Kohms

A simple flex sensor 2.2" in length. As you bend the sensor (flexing), the resistance across the sensor increases.
The resistance of the flex sensor changes when the metal pads are on the outside of the bend (text on inside of bend).

Connector is 0.1" spaced and bread board friendly. Please refrain from flexing or straining this sensor at the base. The usable range of the sensor can be flexed without a problem, but care should be taken to minimize flexing outside of the usable range. For best results, securely mount the base and bottom portion and only allow the actual flex sensor to flex.

How it works

One side of the sensor is printed with a polymer ink that has conductive particles embedded in it. When the sensor is straight, the particles give the ink a resistance of about 30k Ohms
. When the sensor is bent away from the ink, the conductive particles move further apart, increasing this resistance (to about 50k Ohms when the sensor is bent to 90º). When the sensor straightens out again, the resistance returns to the original value. By measuring the resistance, you can determine how much the sensor is being bent.

The simplest way to incorporate this sensor into your project is by using it in a voltage divider. This circuit requires one resistor. Many values from 10K to 100K will work, but we'll use a 10K resistor here. Connect the flex sensor to your microcontroller using the following circuit:

Connect one side of the flex sensor to ground. Connect the other side to your analog input, and use a 10K pullup resistor to VCC.

The resistor and the flex sensor form a voltage divider, which divides VCC by a ratio determined by the two resistances. When the sensor is straight, the 10K resistor and the 30K flex sensor will cause the output voltage to be about 75 percent of VCC. When the sensor is bent, the voltage will increase to about 83 percent of VCC . If you're using 5V for VCC, you should see about 3.75V when the sensor is straight, and about 4.17V when the sensor is bent by 90º. These numbers will vary for individual sensors; for the most accurate results, test your specific sensor and use those numbers in your code.

   The sensor works only in one direction: when it is bent away from the side with the conductive ink (towards the side with the text). You may see a small response when bending in the other direction, but not nearly as much as in the "correct" direction. (If you need to measure bending in both directions, consider using two sensors back-to-back).
       These sensors work best (and last the longest) if they are bent across a large radius, not kinked. Remember that the active area is between the black squares.T
he pin-end of the sensor is susceptible to kinking and eventual failure.It is safe to secure this area so that it doesn't flex along with the rest of the sensor.

Refer to  
           for some excellent tutorials


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