Special:
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[DAT] (requires LDraw-compatible viewer)
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Subject:
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Re: multiplexed touch sensors [was: Re ideas for a RIS 2.0]
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 26 Aug 1999 02:06:19 GMT
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Viewed:
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946 times
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Kekoa Proudfoot <kekoa@pixel.Stanford.EDU> wrote:
> To gauge the touch sensors better, somebody ought to measure what
> sampling rates are reasonable for presses of the touch sensor. And while
> whoever does that is at it, it would also be nice to understand what the
> waveforms look like for short presses.
Okay, I felt like I had some time, so I looked into this a bit. I skipped
the first part and jumped right into measuring a waveform.
I measured a faster waveforms for now, but might give it another go with a
longer waveforms and higher sampling rates later. Here is the waveform
from a short, sharp press/release, where data was collected when the sensor
reading was less than 1000, and the 2 LSBs were set to zero so I could
store data in a byte:
time (ms) reading
--------- -------
0 88
4 80
8 80
12 76
16 76
20 76
24 80
28 80
32 76
36 76
40 72
44 72
48 80
52 188
Here is a more gentle press, as if I were typing:
time (ms) reading
--------- -------
0 500
4 248
8 212
12 168
16 144
20 128
24 116
28 108
32 104
36 96
40 92
44 92
48 88
52 88
56 84
60 84
64 80
68 80
72 80
76 76
80 80
84 76
... ...
152 88
156 88
160 96
164 104
168 128
172 172
176 352
A purposely slow press would of course take even longer to transition.
This should give some idea as to the type of debouncing that should be
needed depending on what you choose as a transition point, what kind of
presses you expect, etc. I will leave other analysis (including maybe a
higher sampling rate) for later because I have to go meet some people for
dinner now.
Also, this data probably does not show everything one might want to
measure, like how much jitter there is around the transition point (or
points, if there is hysteresis in the 0/1 detection) when the sampling rate
is higher, etc.
-Kekoa
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