Flex Sensor
Introduction Flex Sensor:
The flex sensor is an ingenious device employing carbon on a plastic strip to serve as a variable resistor. As the sensor bends in one direction, its resistance varies accordingly. The more it bends, the higher the resistance becomes. This unique property makes it an ideal choice for applications where detecting bending or flexing is necessary. Flex sensor is a tow pin or two terminal device such as p1 and p2. It does not have any polarized terminal like capacitor or diode, means there is no any positive or negative terminal. For power on this flex sensor 3.3V to 5V dc voltage are applied on its terminals and these voltages are gained from interfacing device which could be any type of controller. These voltages are applied according to below table.
Flex senor is a such type of sensor which measures the amount of bending or defection. Actually, it is made up with carbon surface on a plastic strip when this strip is bend or deflect then the resistance of this flex sensor is changed therefore it is also called bend sensor. Because its changing resistance is directly proportional to amount of bend therefore it can also be used as a goniometer. There are two types of flex sensors are currently used in industry according to their size first one is 2.2 inch flex sensor and second one 4.5 inch flex sensor. The resistance and size of both are different but working principle is same .So the appropriate size is chosen according to requirement. Here we are going to discuss 2.2 inch flex sensor. These types of flex sensor have been using in different applications such as in security system, rehabilitation ,computer interface, music interface, servo motor control, intensity control or where the user wants to change the resistance during bending. These are easily available in market or online shop. A simple flex sensor is shown in figure 1Flex Sensor Flex sensor is a tow pin or two terminal device such as p1 and p2. It does not have any polarized terminal like capacitor or diode, means there is no any positive or negative terminal. For power on this flex sensor 3.3V to 5V dc voltage are applied on its terminals and these voltages are gained from interfacing device which could be any type of controller. These voltages are applied according to below table.This sensor device works on the principle of bending strip means when its strip is bend then its resistance is changed which is measured with any controller. Another words, this sensor works like a variable resistance whose resistance is changed when it is bend. This change in resistance depends upon surface linearity, means the resistance of this sensor would be different at different angle such as the resistance would be different when it is flat, the resistance would be different when it is bend 450, similarly the resistance would be different when it is bend 900. These three bending conditions are shown in figure 2Flex Sensor bending conditions.
Spceifications:
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Operating voltage of FLEX SENSOR: 0-5V
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LOW voltages
Power rating: 0.5Watt
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Flat Resistance: 25K
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Bend Resistance Range: 45K to 125K Ohms
Circuit Operation:
As mentioned earlier, FLEX SENSOR is basically a VARIABLE RESISTOR whose terminal resistance increases when the sensor is bent. So this sensor resistance increases depends on surface linearity. So it is usually used to sense the changes in linearity.As shown in the above figure, when the surface of FLEX SENSOR is completely linear it will be having its nominal resistance. When it is bent 45º angle the FLEX SENSOR resistance increases to twice as before. And when the bent is 90º the resistance could go as high as four times the nominal resistance. So the resistance across the terminals rises linearly with bent angle. So in a sense the FLEX sensor converts flex angle to RESISTANCE parameter.
One is constant resistance (R1) and other is variable resistance (RV1). Vo is the voltage at midpoint of VOLTAGE DIVIDER circuit and is also the output voltage. Vo is also the voltage across the variable resistance (RV1). So when the resistance value of RV1 is changed the output voltage Vo also changes. So we will have resistance change in voltage change with VOLTAGE DIVIDER circuit.Flex sensors are usually available in two sizes. One is 2.2 inch and another is 4.5 inch. Although the sizes are different the basic function remains the same. They are also divided based on resistance. There are LOW resistance, MEDIUM resistance and HIGH resistance types. Choose the appropriate type depending on requirement. Here we are going to discuss 2.2inch Flex sensor that is FS-L-0055.
The flex sensor can be used for servo motor control, intensity control or you can use where ever the resistance need to be changed when the bending occurs. Here the circuit constructed with arduino and LED, when the flex sensor bends the intensity of LED changes accordingly.A flex sensor is a device that has very versatile compatibilities. When the sensor is flexed, its resistance increases significantly. Using a voltage divider circuit, comprising of the flex sensor and a carefully chosen fixed resistor, we can know when the sensor is being flexed and when it is not. We will go into extreme detail on how this works.Flex sensors are put into all types of objects, one of the most prominent being stuffed animal toys or dolls, where when you squeeze the arm or other part of its body, it does something such as say a phrase. Flex sensors circuits have also been used in game controllers such as the Nintendo Glove. Thus, they have widespread application and can fit in into many types of circuits .
In the circuit we will build, when the flex sensor is flexed, we will make an LED light up. As soon as we allow the sensor to snap back into its unflexed state, the LED will shut off. So the load of the circuit, which is an LED, will turn on only when the flex sensor is flexed.The flex sensor we will use in this circuit is the 2.2" flex sensor patented and produced by Spectra Symbol.The flex sensor we will use has a flat resistance of 25KO and a bend resistance of 45KO to 125KO, depending on how much it is flexed. The flat resistance is the resistance of the flex sensor when it is unflexed. And the bend resistance is the resistance of the flex sensor when it is bent. The larger the angle that the sensor is bent, the greater the resistance.
If you have a multimeter or an ohmmeter, do a test to check the resistance values you obtain when the sensor is unflexed and flexed. Note these readings. If you do not have a way of checking the resistance yourself, then your next bet is just to follow the datasheet.The datasheet for the 2.2" flex sensor by Spectra Symbol is at the following link: Spectra Symbol 2.2" Flex Sensor Datasheet.The voltage comparator IC we will use is the LM324, since it is a recommended comparator IC to use with the flex sensor on the sensor's datasheet. This is a quad op amp comparator; however, in this circuit, we will just be using one op amp.
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How the Flex Sensor Work:
Since the flex sensor has a flat resistance of 25KO and a bend resistance of 45KO to 125KO, we want a fixed resistor that has a value between these 2 resistance values (the flat and the bend). So for this sensor, we will use a 33KO resistor. When the sensor is unflexed, its resistance will be below 33KO. When it is flexed, it will be above 33KO. We'll explain how this works specifically with our voltage comparator IC.Our voltage comparator IC, the LM324, has 4 op amps. But we will just be using one of them. Each op amp has 2 inputs and 1 output. The 2 inputs are an inverting terminal and a noninverting terminal. How the op amp works is when the voltage at the inverting terminal is greater than at the noninverting terminal, then the output is drawn high to Vcc and the load is powered. When the voltage at the inverting terminal is less than the noninverting terminal, then the output is drawn low to GND and the load cannot be powered. This is how an op amp works.
The flex sensor and the fixed resistor, to the inverting terminal of the op amp. To the noninverting terminal, we connect the wiper terminal of a potentiometer. One end of the potentiometer we connect to Vcc and the other end we connect to ground. Vcc will be about 5V. Adjust the potentiometer so that it is adjusted about midway so that it has a voltage of about Vcc/2, or 2.5V.
With this setup, our circuit will work. When the flex sensor is not flexed, its resistance is 25KO, below the 33KO fixed resistor. Thus, most of the voltage from the VCC power supply will fall across the fixed resistor, well more than half, and very little voltage falls across the flex sensor. Thus, the voltage at the inverting terminal will be lower than the 2.5V at the noninverting terminal. Since the voltage at the inverting terminal is lower than at the noninverting terminal, the output will be drawn down to GND and the load, which is an LED, will be off.When the flex sensor is flexed, however, its resistance increases significantly, well above the 33KO fixed resistor. Thus, most of the voltage from VCC will fall across it. Thus, in this case, the voltage at the inverting terminal will be greater than at the noninverting terminal, and the output will be drawn up to VCC, so the LED will be powered on.
A flex sensor or bend sensor is a sensor that measures the amount of deflection or bending. Usually, the sensor is stuck to the surface, and resistance of sensor element is varied by bending the surface.A flex sensor is a kind of sensor which is used to measure the amount of defection otherwise bending. The designing of this sensor can be done by using materials like plastic and carbon. The carbon surface is arranged on a plastic strip as this strip is turned aside then the sensor’s resistance will be changed. Thus, it is also named a bend sensor. As its varying resistance can be directly proportional to the quantity of turn thus it can also be employed like a goniometer.
Frequently Asked Questions
How do I know if my flex sensor is working?
As Flex sensor is a variable resistor, it can be read by connecting it with a fixed value resistor 10kO. This forms a voltage divider network. One end of the flex sensor is connected to GND while the other end is connected to Analog Input A0 of Arduino. A 10KO resistor is connected between A0 and +5V.
What is the output of flex sensor?
Elements. As a variable printed resistor, the Flex Sensor achieves great form-factor on a thin flexible substrate. When the substrate is bent, the sensor produces a resistance output correlated to the bend radius—the smaller the radius, the higher the resistance value.
How does sensor device work?
A sensor converts the physical action to be measured into an electrical equivalent and processes it so that the electrical signals can be easily sent and further processed. The sensor can output whether an object is present or not present (binary) or what measurement value has been reached (analog or digital).
What is sensor resolution?
The sensor resolution or measurement resolution is the smallest change that can be detected in the quantity that it is being measured. The resolution of a sensor with a digital output is usually the numerical resolution of the digital output.
Why is sensor used?
Sensors can improve the world through diagnostics in medical applications; improved performance of energy sources like fuel cells and batteries and solar power; improved health and safety and security for people; sensors for exploring space and the known university; and improved environmental monitoring.
