New wishlist item: Side-mounted touch strip sensor

thomas.cooksey at thomas.cooksey at
Wed Jun 20 00:48:33 CEST 2007

Ok, there seems to be 2 other possibilities, a rocker switch and a scroll wheel.

Rocker switch: Have you ever used a cheap mouse with a rocker switch instead of a scroll wheel? If you have then you know how limited they are. They simply do not offer the same amount of control a scroll wheel or touch strip does.

Scroll wheel: A scroll wheel is much better, which is why mice use them. They can provide mechanical feedback and give the user far more control over their scrolling adventures.

However, the image on the screen scrolling will be enough feedback. I used to work for HP in their research center (HP Labs). While there I worked on a prototype ebook reader. To maximise the readability of the display, the device doesn't have a touchscreen. Instead it has touch strips around the outside of the screen. To turn a page you drag your finger along the strip and see the page turning as you move your finger. Stop moving your finger and the page stops turning. The feel of the interface was awesome. Some pics here: although without a video it's hard to gauge just how well it works. (I actually wrote the touch strip calibration software and the "bookshelf" application on the device the bloke is holding in the first picture. :-) )

So given that the visual feedback is adequate, a touch strip does give you more than a scroll wheel. First, the strip can be quite long, although I guess you'd only want it between 25-40mm. It also gives you a resolution of 128 different positions, allowing very precise (pixel-by-pixel) control of the image you are scrolling. I've just tried my own mouse's scroll wheel, which, in a single finger "swipe", gives me 8/9 different positions. That's a whole lot more control. I guess one problem with pixel-by-pixel scrolling is CPU power. Without a hardware blitter, I doubt the GTA01 has enough processing power to give smooth scrolling. Roll on GTA02. :-)

As for power & jogging the touch strip accidentally, well, the controller provides a stand-by mode. When the phone is locked, the strip controller is placed in standby. Why would you ever want to have a scrolling input device wake it up? Also, while I'm on the subject, please tell me that the GTA01 is not woken up by touchscreen interupts??? To have a complete resistive touchscreen and it's associated controller powered up all the time must make quite an impact on power consumption?!?!? Or does it poll the touch screen every 500ms or so while locked?

Judging from some odd replies I should probably clarify that this is a 1D, one dimensional sensor. It's not a touch pad and IMO, a side mounted touch pad makes no sense. I also agree with people who say there should be some buttons. I think a touch strip combined with 2 buttons (select & back) is all you need or want for menu navigation. I also think the 2 buttons should complement the touch strip in such a way that the device can be used single handedly.

The sensor controllers I first posted use either I2C or SPI so technically could be retrofitted. The only problem is that the Analog part (my preferred part) is only available as "pain-in-the-bottom" to solder 4x4mm surface mount packages, which is beyond my skill to solder. :-( Also, these are very specialist multi-element capacitive sensors. A general purpose uc is not able to detect the tiny changes in capacitance between sensor elements. The chips contain very complicated and sensitive self-calibration and environmental compensation circuitry which cannot be replicated. 



More information about the community mailing list