This document is a seminar report on flex sensors presented by Vatsal Shah to Ankur Rathi at Indus University. It includes the theoretical background of flex sensors, how they work as variable resistors whose resistance changes with bending, simulation results showing changing voltage output with bending, electrical characteristics, applications in toys, auto controls, fitness and medical devices, and a flex sensor Arduino project using 10 LEDs.

1. EMI-EC410502
Flex Sensor
Electronics & Communication Department
9/27/2014
Flex Sensor

2. 1
Vatsal Shah Indus University Flex Sensor
A
Seminar Report
On
“Flex Sensor”
Vatsal Shah
Electronics and Communication Engineering Department
5th Semester
IU1241090055
Indus Institute of Technology and Engineering
Submitted to:- Submitted by:-
Ankur Rathi Vatsal Shah.
Asst. Prof.
EC Dept.

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Vatsal Shah Indus University Flex Sensor
Contents
1.0 Theoretical background...............................................................................................3
2.0 Schematics....................................................................................................................4
3.0 How they Work?............................................................................................................5
4.0 Simulation and results .................................................................................................6
5.0 Electrical Characteristics.............................................................................................7
6.0 Problems........................................................................................................................7
7.0 Application.....................................................................................................................8
8.0 Project ............................................................................................................................9
9.0 Reference..................................................................................................................... 10

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Vatsal Shah Indus University Flex Sensor
1.0 Theoretical background
A Flex and Force sensor. This is a flexible sensor which changes its output
when it is bent or when force is applied on it. This sensor has two output wires. The
resistance between these two wires varies when the sensor is bent or when
subjected to a force. Hence, this sensor can be used as a flex or force sensor. When
the sensor is kept straight with no force acting on it, it has a resistance of around 10
K Ohms.
When the sensor is bent in either way, or when force is applied on the sensor,
the resistance between these two wires increases proportionally to the amount of
bending. They convert the change in bend to electrical resistance - the more the
bend, the more the resistance value. They are usually in the form of a thin strip from
1"-5" long that vary in resistance from approximately 10 to 50 K ohms.

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Vatsal Shah Indus University Flex Sensor
2.0 Schematics
Flex Sensor as Voltage Divider - Output voltage increases with the bend. The
impedance buffer in the circuit reduces error due to source impedance of the flex
sensor as voltage divider. Suggested op amps are the LM358 or LM324. We can
also test our flex sensor using simple test, and skip op-amp.

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Vatsal Shah Indus University Flex Sensor
3.0 How they Work?
Flex sensors are analog resistors. They work as variable analog voltage
dividers. Inside the flex sensor are carbon resistive elements within a thin flexible
substrate. When the substrate is bent the sensor produces a resistance output
relative to the bend radius. With a typical flex sensor, a flex of 0 degrees will give
10K resistance will a flex of 90 will give 30-40 K ohms. The Bend Sensor lists
resistance of 30-250 K ohms.
.

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Vatsal Shah Indus University Flex Sensor
4.0 Simulation and results0.51.52.5
9 14 19 24
Voltage(V)
Resistance (Kohm)
Voltage vs Resistance

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Vatsal Shah Indus University Flex Sensor
5.0 Electrical Characteristics
 Size: approx. 0.28" wide and 1"/3"/5" long
 Resistance Range:1.5-40K Ω
 Temperature Range: -35 to +80°C
 Voltage: 5 to 12 V
6.0 Problems
 Only one working flex sensor
 Reduced accuracy to differentiate between gestures
 Broke due to heat

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Vatsal Shah Indus University Flex Sensor
7.0 Application
The Bend Sensor technology has many potential applications in the
consumer products sector. A key marketing strategy is to pursue product applications
that emphasize functionality, reliability, quality, and user convenience.
Such products might include computer peripherals (mouse, key board,
controllers, input devices, laptop controls, etc.), communications equipment (cellular
phones), small and large appliances (high temperature switches, safety controls, on/off
switches, balance controls).
 Toys
o In 1998, the Company produced over 7,000,000 Bend Sensors for
incorporation into several lines of interactive plush toys.
 Auto Control
 Fitness Products
 Gaming Glove
 Medical
o In the medical product area, such applications might include infusion pumps,
respiratory therapy equipment, obstetric equipment, rehabilitative and
physical therapy equipment, pelvic stabilization devices, Pressure-Monitoring
Devices, etc.
 Horn Switch
o The Flex point sensor is a thin sheet of screen-printed plastic that can be
laminated between the air bag assembly and a flexible cover on the steering
wheel. The device can be placed over the air bag assembly on the steering
wheel in place of the traditional switch that has been placed on the side of the
air bag assembly, thus eliminating the frustration and design waste
associated with the need for button switches.

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Vatsal Shah Indus University Flex Sensor
8.0 Project
The parts required:
 Arduino UNO
 10 x Red LEDs
 9 x 330 Ohm resistors for the LEDs
 1 x 10K Ohm resistors for the flex sensor.
 1 x Flex sensor
 Wires and Breadboard to connect it all together

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Vatsal Shah Indus University Flex Sensor
9.0 Reference
 http://sensorwiki.org/doku.php/sensors/flexion
 http://itp.nyu.edu/physcomp/sensors/Reports.Flex
 http://www.flexpoint.com/companyInfo/about.htm
 https://www.youtube.com/watch?v=ZJiwaAKHMNw
 https://www.sparkfun.com/products/10264
 http://www.instructables.com/id/How-to-Make-Bi-Directional-Flex-Sensors/
 http://www.imagesco.com/sensors/flex-sensor.html
 http://infusionsystems.com/catalog/product_info.php/products_id/54
 http://www.digikey.com/us/en/ph/SpectraSymbol/flex_sensor.html
 http://www.adafruit.com/products/182
 https://www.inventables.com/technologies/bend-sensor
 http://devices.sapp.org/component/flex/
 http://www.nskelectronics.com/flex_sensor.html
 http://arduinobasics.blogspot.in/2011/05/arduino-uno-flex-sensor-and-leds.html