Monday, September 1, 2008

Re: [applekeynote] MacBook Air: 3. trackpad interference with projector

I asked:

>In normal use the large trackpad on the MacBook Air works fine.
>However, I have found that when the computer is connected to a
>videoprojector there is some sort of electrical interference that
>makes it very difficult to place the cursor exactly. Instead of
>moving smoothly as I move my finger it jerks around almost
>uncontrollably. Although this doesn't matter during a presentation,
>because I don't usually use the trackpad during a presentation, it
>does matter at the start. I have found an easy solution, however,
>that seem to work perfectly on my computer. If I touch the computer
>with my left hand at the left of the trackpad, while manipulating the
>trackpad with the right hand (a left-handed person would doubtless do
>it the otrher way around), the trackpad becomes perfectly stable and
>as I don't need my left hand for anything else while I'm using the
>trackpad that seems, at least for the moment to be the complete
>solution.

To which Frank Bruce replied:
>
>Sound like a grounding issue in your MB Air
>Is the table or the surface where the MB-Air is resting metallic?
>wood? plastic?
>Is the projector yours?

You are perfectly correct, and I should have thought of this myself.
The projector (the same one I have used many times) has a plastic
case and a two-pin power supply, so it is not earthed. In the past,
however (pre-Air) I always had the computer connected to mains power
because I didn't trust the battery. On the occasion referred to,
however, I was running the computer off the battery, because it was
new enough that it oughtn't to have battery problems, and because
this was a practice not a real presentation. After reading your
suggestion I checked that the problem persists if the computer is not
plugged in, but disappears when it is.

Moral: don't run the computer off its battery during a presentation!


--
Athel Cornish-Bowden
acornish@ibsm.cnrs-mrs.fr

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