TouchPad technologies: a question of size, cost and performance
There appears, of course, to be a ready-made model for the automotive touchpad: touchpads in laptops are based on proven capacitive sensing technology which has been developed, over a period of many years, to support large touch surfaces and multi-finger inputs, and to recognise gestures. Capacitive sensing touchpads are extremely light, thin and robust. Laptop manufacturers can readily calibrate the sensitivity of the touchpad so that it responds quickly to user inputs without suffering from interference caused by stray capacitance.
Automotive suppliers, however, encountered difficulties in early attempts to implement capacitive touchpads in cars. Briefly, car makers experimented with a touchpad in the centre console, before touchscreens were commonly adopted. A touch input device that required the driver to take a hand off the steering wheel was never likely to find favour, however.
The requirement, then, was clearly for steering wheel-mounted touchpads. But an attribute of conventional capacitive sensing touchpads that provides an advantage in laptop computers – their high sensitivity – becomes a drawback in the car: because the touchpad is sensitive to the slightest touch, there is a risk that it will register inadvertent touch events as drivers shift the position of their hands on the steering wheel in the normal course of driving.
A Mercedes Benz response to this problem has been to take a different technological route altogether, demonstrating at the 2016 Consumer Electronics Show an optical finger navigation (OFN) touchpad mounted on the steering wheel. OFN technology performs well, but suffers from various drawbacks from the point of view of automotive applications. It is:
- vulnerable to optical interference from ambient light sources including sunlight;
- apt to cause irritation