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IBM wrote:A properly implemented TrackPoint will never drift when it is not in use. However, the user may defeat the drift control algorithms in two way:
1. The user may keep a finger on the stick for a long enough period that the zero-force signal drifts out of the dead band; how long this is depends on the rate of drift, e.g. the rate of temperature change. Then the cursor will be found to be drifting when the stick is finally released. The circuit will rezero and the cursor will stop in a few seconds. provided it is left alone; if the user keeps trying to hold the cursor still, it can go on indefinitely.
2. The user may be able to apply a very steady force (usually a very low force, as in slowly scanning down a list) for a long enough time to fool the TrackPoint into rezeroing improperly. The cursor stops, and when released moves in the opposite direction for a few seconds, as in the 'rubber band test'. Again, it recovers if left alone for the requisite three seconds.
Both of these cursor drift modes are part of the TrackPoint's normal function. They could be eliminated, but at the cost of occasionally reaching a state in which cursor drift occurs and does not spontaneously recover.
Another cause of drift is RF interference - for example from a nearby cell phone, or even worse a cell phone transmitter inside the same box. The problem comes from rectification of RF in the op amps, and can usually be cured by placing small bypass capacitors (50 - 100 pF) directly across the input pins of each op amp section.
I have also seen and had it happen were the trackpoint CAP goes "off-center" and can cause the cursor drift. Removing and "re-setting" the cap on the pointing stick seems to solve the problem...GomJabbar wrote:Notes on TrackPoint Drift
IBM wrote:A properly implemented TrackPoint will never drift when it is not in use. However, the user may defeat the drift control algorithms in two way:
1. The user may keep a finger on the stick for a long enough period that the zero-force signal drifts out of the dead band; how long this is depends on the rate of drift, e.g. the rate of temperature change. Then the cursor will be found to be drifting when the stick is finally released. The circuit will rezero and the cursor will stop in a few seconds. provided it is left alone; if the user keeps trying to hold the cursor still, it can go on indefinitely.
2. The user may be able to apply a very steady force (usually a very low force, as in slowly scanning down a list) for a long enough time to fool the TrackPoint into rezeroing improperly. The cursor stops, and when released moves in the opposite direction for a few seconds, as in the 'rubber band test'. Again, it recovers if left alone for the requisite three seconds.
Both of these cursor drift modes are part of the TrackPoint's normal function. They could be eliminated, but at the cost of occasionally reaching a state in which cursor drift occurs and does not spontaneously recover.
Another cause of drift is RF interference - for example from a nearby cell phone, or even worse a cell phone transmitter inside the same box. The problem comes from rectification of RF in the op amps, and can usually be cured by placing small bypass capacitors (50 - 100 pF) directly across the input pins of each op amp section.