Senseur FSR

Introduction

FSRs are sensors that allow you to detect physical pressure, squeezing and weight. They are simple to use and low cost. This is a photo of an FSR, specifically the Interlink 402 model. The 1/2" diameter round part is the sensitive bit.

Tester un FSR

The easiest way to determine how your FSR works is to connect a multimeter in resistance-measurement mode to the two tabs on your sensor and see how the resistance changes. Because the resistance changes a lot, a auto-ranging meter works well here. Otherwise, just make sure you try different ranges, between 1 Mohm and 100 ohm before 'giving up'.

Brancher un FSR

Because FSRs are basically resistors, they are non-polarized. That means you can connect them up 'either way'a and they'll work just fine!

Dans un breadboard

FSRs are often a polymer with conductive material silk-screened on. That means they're plastic and the connection tab is crimped on somewhat delicate material. The best way to connect to these is to simply plug them into a breadboard.

Un connecteur femelle

or use a clamp-style connector like alligator clips, or a female header.

Un bornier

or a terminal block such as Phoenix #1881448

Utiliser un FSR

Méthode par lecture Analogique de la tension

The easiest way to measure a resistive sensor is to connect one end to Power and the other to a pull-down resistor to ground. Then the point between the fixed pulldown resistor and the variable FSR resistor is connected to the analog input of a microcontroller such as an Arduino (shown).

For this example I'm showing it with a 5V supply but note that you can use this with a 3.3v supply just as easily. In this configuration the analog voltage reading ranges from 0V (ground) to about 5V (or about the same as the power supply voltage).

The way this works is that as the resistance of the FSR decreases, the total resistance of the FSR and the pulldown resistor decreases from about 100Kohm to 10Kohm. That means that the current flowing through both resistors increases which in turn causes the voltage across the fixed 10K resistor to increase. Its quite a trick!

Force (lb)	Force (N)	FSR Resistance	(FSR + R) ohm	Current thru FSR+R	Voltage across R
None	None	Infinite	Infinite!	0 mA	0V
0.04 lb	0.2 N	30 Kohm	40 Kohm	0.13 mA	1.3 V
0.22 lb	1 N	6 Kohm	16 Kohm	0.31 mA	3.1 V
2.2 lb	10 N	1 Kohm	11 Kohm	0.45 mA	4.5 V
22 lb	100 N	250 ohm	10.25 Kohm	0.49 mA	4.9 V

This table indicates the approximate analog voltage based on the sensor force/resistance w/a 5V supply and 10K pulldown resistor.

Note that our method takes the somewhat linear resistivity but does not provide linear voltage! That's because the voltage equasion is:

Vo = Vcc ( R / (R + FSR) )

That is, the voltage is proportional to the inverse of the FSR resistance.

Source

• Ce tutoriel d'AdaFruit (en anglais)
• Source des images LadyAda (ici chez AdaFruit). Licence Attribution-ShareAlike Creative Commons

Où Acheter

• Le Senseur FSR est disponible chez MCHobby
• Le senseur Flex est également disponible chez MCHobby.
• MC Hobby vous propose également des borniers et breadboard visible sur cette page.

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Traduit avec l'autorisation d'AdaFruit Industries - Translated with the permission from Adafruit Industries - www.adafruit.com