A simple Flex Sensor is 2.2" in length. As the sensor is flexed, 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. The value of the output depends on the bending of the sensor hence, the output we get is an analog value and this output can be send to ADC IC or of Controller.
Working and Modifications
-    The Bending and resistance value are directly related to each other as  :
                o    Flat (nominal resistance)
                o    45 degree Bend (increased resistance)
                o    90 degree Bend (resistance increased further)
-    An Op - Amp is used and outputs either high or low depending on the voltage of the inverting input.
     In this way you can use the flex sensor as a switch without going through a microcontroller.
-    A potentiometer can be added to the circuit to adjust the sensitivity range.
-    Use the sensor as the input of a resistance to voltage converter using a dual
     sided supply Op - Amp. A negative reference voltage will give a positive output.
     Should be used in situations when you want output at a low degree of bending.

A simple Flex Sensor is 2.2" in length. As the sensor is flexed, 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. The value of the output depends on the bending of the sensor hence, the output we get is an analog value and this output can be send to ADC IC or of Controller.
Working and Modifications
-    The Bending and resistance value are directly related to each other as  :
                o    Flat (nominal resistance)
                o    45 degree Bend (increased resistance)
                o    90 degree Bend (resistance increased further)
-    An Op - Amp is used and outputs either high or low depending on the voltage of the inverting input.
     In this way you can use the flex sensor as a switch without going through a microcontroller.
-    A potentiometer can be added to the circuit to adjust the sensitivity range.
-    Use the sensor as the input of a resistance to voltage converter using a dual
     sided supply Op - Amp. A negative reference voltage will give a positive output.
     Should be used in situations when you want output at a low degree of bending.