User:Darya1970/my FSR

A force-sensitive resistor (FSR) has a variable electrical resistance as a function of applied pressure.

FSRs are fabricated with elastic material in four layers, consisting of:

• A layer of electrically insulating plastic;
• An active area consisting of a pattern of conductors, which is connected to the leads on the tail to be charged with an electrical voltage;
• A plastic spacer, which includes an opening aligned with the active area, as well as an air vent through the tail;
• A flexible substrate coated with a thick polymer conductive film, aligned with the active area.

When external force is applied to the sensor, the resistive element is deformed against the substrate. Air from the spacer opening is pushed through the air vent in the tail, and the conductive material on the substrate comes into contact with parts of the active area. The more of the active area that touches the conductive element, the lower the resistance. All FSRs exhibit a "switchlike response", meaning some amount of force is necessary to break the sensor's resistance at rest (approximately 1 MΩ), and push it into the measurement range (beginning at approximately 100 KΩ).

Operationally, an FSR is very similar to a strain gauge, the main difference being that a strain gauge's backing deforms with the resistive element, while an FSR's does not. This fact is important to consider when mounting an FSR against a support, as discussed below.

The same applied force will result in a wider output swing in an FSR than a strain gauge. Strain gauges, however, have higher accuracy than an FSR. Depending upon the particular needs of the application, one may choose one or the other. Ultimately, a major consideration in the choice of a sensor is cost; a major advantage of FSRs is their low cost.

Using an FSR

One of the most common circuits implemented to utilize an FSR's output is the voltage divider. A voltage (usually +5 V) is applied to one of the leads, while the other is grounded. FSRs are not polar, meaning it does not matter which side receives the voltage. One lead from a second resistor (with fixed value) is then connected to the voltage side, while the other lead of the second resistor is also connected to ground. In this way the FSR is able to measure the "voltage drop across a resistor". The resistance value of the second resistor determines the output range of the sensor. Typically, 100 KΩ will yield a sensor output suitable for common ADCs used for musical applications.

Mounting

Because the FSR's operation is dependent on its deformation, it works best when affixed to a support that is firm, flat, and smooth . Mounting to a curved surface (as is often the case when placing sensors on the body or clothing, especially on a dataglove) reduces measurement range and resistance drift. One solution is to use a sensor with a smaller active area, since less of the sensing area will be deformed by the contours of the body. Bending the tail will also affect performance because the air vent will be deformed. The tail is also relatively fragile, and if bent far enough the conductive leads inside it will break, rendering the sensor useless and irreparable.

Output

The usable range of an FSR's output signal is linear. If enough force is applied, its response becomes nonlinear due to sensor saturation. After this point output will not be significantly affected by an increase in applied pressure. This sensor is known to have poor accuracy, with errors up to 25% of output.

FSR suppliers

• Interlink Electronics, [1]
• IEE (UK), [2]
• Tekscan, [3]

Links and References

External links

• W. Putnam and R.B. Knapp, Input/Data Acquisition System Design for Human Computer Interfacing. The Stanford University Center for Computer Research in Music and Acoustics, 1996 [4]
• A. Desai, S. Payandeh, J. Vaisey, Sch. of Eng. Sci., Simon Fraser Univ., Burnaby, BC, Canada, On the localization of objects using an FSR pressure pad transducer. In: Systems, Man, and Cybernetics, 1994, 'Humans, Information and Technology', 1994 IEEE International Conference on, Publication Date: 2-5 Oct. 1994, vol.1, pp 953 - 957 

• A. Bolduc, G.L. Beauregard, J.R. LaCourse, Dept. of Electr. & Comput. Eng., New Hampshire Univ., Durham, NH, USA, A method of measuring finger pressure during keyboard data entry. In: Instrumentation and Measurement Technology Conference, 1992. IMTC '92., 9th IEEE, Publication Date: 12-14 May 1992, pp 57 - 58 

• S.I. Yaniger, Interlink Electronics, Inc., Force Sensing Resistors: A Review Of The Technology. In: Electro International, 1991, pp 666 - 668 

• A. Nikonovas, A.J.L. Harrison, S. Hoult, D. Sammut, University of Bristol Department of Mechanical Engineering Bristol, UK and North Bristol NHS Trust Frenchay Hospital Bristol, UK, The application of force-sensing resistor sensors for measuring forces developed by the human hand. In: Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, Number 2/2004 Volume 218, pp 121-126