Sensors technology used in Lenovo TrackPoint? - Page 1
Forum section: electronics / beginners

author: m4rtin
author_rank: Regular Contributor
timestamp: August 02, 2015, 11:33:27 pm
content: Lenovo(and some other laptop manufacturers) include aTrackPointto their keyboards. If this red button is pushed harder to sides then the cursor on the screen moves faster. PCB, which has the sensors and controller IC, can be seenhere. As seen from the picture, there are four small black sensors. What kind of sensors are those? How do they work?

author: krivx
author_rank: Frequent Contributor
timestamp: August 03, 2015, 12:08:53 am
content: I think those are just buttons. The black squares are conductors that close PCB traces when pushed down.

author: dentaku
author_rank: Frequent Contributor
timestamp: August 03, 2015, 01:50:44 am
content: Here's IBM's old patent document from 1997.http://www.google.com/patents/US6115030Quote from: m4rtin on August 02, 2015, 11:33:27 pm

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2015, 09:15:35 am
content: Always wondered why the trackpoint on my old IBM Thinkpad was still working just as well after 12 years of use, despite wearing out several rubber caps. Reassuring to know that it's capacitive rather than resistive. It's far more responsive to degree of pressure than just switch action.I just hope I can still find a laptop with one when I'm finally forced to change it (just can't get on with those touchpad things).Glad you asked the question, I never thought to look it up.

author: amyk
author_rank: Super Contributor
timestamp: August 03, 2015, 12:05:05 pm
content: It's a strain gauge. There used to be a page on IBM's site with detailed information about it but it looks like it got removed sometime recently.

author: m4rtin
author_rank: Regular Contributor
timestamp: August 03, 2015, 12:20:36 pm
content: Quote from: krivx on August 03, 2015, 12:08:53 amI madeanother picturefrom the other side of the PCB. I could easily be wrong, but I don't see a way how those black squares could close the traces. In addition, IMHO there should be a method to detect the amount of pressure applied to joystick.

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2015, 01:05:04 pm
content: QuoteHmm, so the original patent (in previous link) refers to capacitive sensing, but you're saying that IBM moved to resistive strain gauge sensing? (as Wikipedia describes it). There must be another patent somewhere then.I saw references to different generations eg. Trackpoint III and Trackpoint IV. As you say, the IBM page has gone, the links to it are dead.

author: mikerj
author_rank: Super Contributor
timestamp: August 03, 2015, 04:04:53 pm
content: Quote from: Gyro on August 03, 2015, 01:05:04 pm"Strain gauge" doe not imply a resistive sensor. They can be capacitive, resistive or peizo based.

author: Gyro
author_rank: Super Contributor
timestamp: August 03, 2015, 04:35:24 pm
content: Ah, fair point, I got distracted by the resistive reference in the Wikipedia entry.I'm curious about the possibilities of capacitive strain gauges now - the Trackpad has almost no discernible movement and the circuit in the patent is pretty basic given the small size of the device - single gate RC oscillators and a PIC.

author: m4rtin
author_rank: Regular Contributor
timestamp: August 03, 2015, 11:18:32 pm
content: Quote from: mikerj on August 03, 2015, 04:04:53 pmAm I correct that by "strain gauge" you meant that if I pushed the joystick for example forward, then the traces connected to theupper black squaregot shorter and thus had less resistance which allowed more current to pass and thus detect that joystick is pushed forward? And if joystick is pushed harder, then the resistance is even lower which eventually results in faster cursor movement? I could easily be wrong, but that's how I understood it fromWikipedia drawing.