Web Site: www.parallax.com Office: (916) 624-8333 Forums: forums.parallax.com Fax: (916) 624-8003 Sales: sales parallax.com Sales: (888) 512-1024 Technical: support parallax.com Tech Support: (888) 997-8267 FlexiForce Sensor Demo Kit ( 30056) The FlexiForce A201-25 Sensor from Tekscan is piezoresistive force sensor capable of measuring up to 25 lbs of force, perpendicular to its sensing plane. In an electrical circuit, this sensor will act as a variable resistor, where the change in resistance is inversely proportional to the force applied. The change in resistance can be measured by a simple RC decay circuit, readable by any Parallax microcontroller. Application Ideas Features y Touch pads y Measure both static and dynamic y Alarm systems forces y Airbag force measurement y Simple RC circuit interface y Compression moldings y Capable of measuring a total applied force of 25 lbs Packing List y Requires at least 1 PSI on sensing area Verify that your FlexiForce Demo Kit has the y Versatile small size following components: y Ultra-thin, flexible printed circuit y (1) FlexiForce Sensor y Compatible with all Parallax microcontrollers y (1) 220 resistor y (1) 0.1 F capacitor Key Specifications y (1) 0.01 F capacitor y Communication: Variable resistance inversely proportional to applied force y Operating temperature: 15 to 140 F (-9 to 60 C) y Dimensions: 8.00 x 0.55 x 0.008 in (203 x 9.53 x 0.208 mm) Copyright Parallax Inc. Flexiforce Sensor Demo Kit ( 30056) v1.0 3/1/2010 Page 1 of 3 Device Information Theory of Operation The FlexiForce Sensor uses a resistive-based technology, and reads forces perpendicular to its sensing plane. Its active sensing area is a 0.375 diameter circle located at the top of the sensor. When the sensing area is unloaded, the resistance is very high (greater than 5 M) and the resistance decreases to approximately 20 k as force is applied. Connecting and Testing The two outer pins of the connector are active, while the center pin is inactive. By connecting an ohmmeter to the outer two pins, the output resistance of the sensor can be measured. Conditioning Before using the FlexiForce Sensor for the first time or after long periods of inactivity, it is highly recommended that it be conditioned in order to stabilize the output resistance. The output resistance can fluctuate over the first few tests, and conditioning the sensor ensures repeatable results. To condition the FlexiForce sensor, place 110% of the maximum test weight on the active sensing area and let it sit for a few minutes. Repeat this process another four to five times to guarantee accurate results. Sensor Loading The active sensing area of the FlexiForce Sensor should be treated as a single contact point, with the load distributed evenly across the sensing area. For best results, the loaded area should cover 70-100% of the sensing area and apply a minimum of 1 PSI. If the load is smaller than the active sensing area, make sure the load is centered in the sensing area and not near the edges. If the load is larger than the active sensing area, you may need to make use of a puck. A puck is a piece of rigid material smaller than the active sensing area that is placed between the object and the sensing area. This will cause the load path go through the puck to increase the PSI, resulting in more accurate measurements. Connection Diagram Copyright Parallax Inc. Flexiforce Sensor Demo Kit ( 30056) v1.0 3/1/2010 Page 2 of 3