Capacitive Sensor Slider Advice

[johnnyfp]

Hi,

I've been shopping around looking for a Capacitive Sensor that can do Slider type sensing.

http://www.smsc.com/index.php?tid=38&pid=275&cid=&tab=5 looks promising as they seem to offer low pin count and a SPI/I2C Slave output. I just want some simple finger sensing that I can hook into my existing MCU and tell me where it is so I can work out a light level.

The one thing I'm unsure about is the Sensing for a Slide. Specifically the number of channels. I've seen many PCB designs that have five or more arrow shaped pads, that hook up to one of these chips, and presumably the MCU works out where your finder is. But these tend to be the higher number of channel and more pin count chips. So why don't they have a tapered pcb track, where it's narrow at the bottom and wide at the top to measure the slide value and use minimal of channels?

Cheers

Jfp.