Force-sensing resistor enables designs for the “ring” cycle
By Bill Schweber -- EDN, March 31, 2005
Apple’s iPod form factor and user interface has made the scroll wheel the user input of choice for many handheld devices. With the MicroNav Ring from Interlink Electronics, designers get a resistance-based alternative transducer for similar applications (Picture). The 43-mm-diameter force-sensing resistor, with a 13-mm center hole for click-switch placement, provides 360° of coverage. It survives 2 million taps of 500g and the same number of complete apparent revolutions and yields angle measurement to ±3°. Through software interpretation, it functions as an absolute and a relative positive sensor.
Power consumption is critical in most of the target applications, and the sensor looks like an open circuit in the untouched state. Further, according to Keith M Roberts, director of corporate communications, “Unlike a capacitive device, this does not have moisture issues, and it is a lot more energy efficient, since it does not have to support an electric field.” For example, the transducer samples current consumption 40 times/sec at a peak rate of 0.3 mA and an average rate of 0.1 μA. The ring sells for $1 to $2 (OEM quantities). The vendor supplies the software to synthesize any series of sequential resistance readings into a coherent statement of the user intentions.
Interlink Electronics, www.interlinkelectronics.com.
