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Subject: 
Re: multiplexed touch sensors [was: Re ideas for a RIS 2.0]
Newsgroups: 
lugnet.robotics
Date: 
Thu, 26 Aug 1999 02:06:19 GMT
Viewed: 
946 times
  
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



Message is in Reply To:
  Re: multiplexed touch sensors [was: Re ideas for a RIS 2.0]
 
(...) I don't doubt that there are reasonable creations that e.g. press a touch sensor button halfway for extended periods of time, but I can't think of any off the top of my head. Can anybody help me out here? My point was that in what I would (...) (25 years ago, 26-Aug-99, to lugnet.robotics)

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