You have to hand it to Alps for managing to make a surface-mount force sensor that is only 1.50 x 0.85 x 0.68mm while maintaining 2% of full scale linearity.

Alps-Alpine-Stylus-force-sensor

The company is aiming at the business ends of force-sensitive drawing styli with the HSFPAR007A, as it will be know. It follows on from a larger (2 x 1.6mm) HSFPAR004A model introduced early year.

“The new product is small enough to fit in the slimmer stylus pens used for smartphones,” according to the company, which sees tablets and the trend for larger screens on phones driving demand for styli: “Bigger displays lead to the emergence of many new drawing applications for smartphones and the use of stylus pens, allowing more detailed and diverse input. In March 2019, Alps Alpine commenced production of the HSFPAR004A force sensor, which fits into the tip of a stylus pen for tablet PCs to enable accurate reproduction of drawing thickness corresponding to the pressure applied. It has been well received by customers.”

Alps-Alpine-sylus-force-sensor-graphChallenges at the tip of a stylus include combining sensitivity and linearity with impact and overload resistance.

The company is claiming to register force from 10mN to 8N with its 2% linearity, and to combine this measurement capability with a life of one million cycles (at 8N) and an overload rating of 55N.

Supply voltage is 1.5-3.6V, and the output is 2.5mV/V/N.

It has “outstanding impact resistance, achieved with a load-distributing design, and the structure is unaffected by external magnetic or electric fields”, according to Alps.

As well as in the tip of a stylus, use if foreseen embedded beneath a touch panel or capacitive sensor to measure force applied or detect accidental operation.

Thanks to Pawel W (who commented below) for finding the data sheet, which shows that it is a piezoelectric bridge sensor and offers an interface circuit to go with it, with options for various differential amplifier chips.