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[DPRG] pressure sensors on the cheap

Subject: [DPRG] pressure sensors on the cheap
From: Dan Gates topazx2 at yahoo.com
Date: Mon Jan 5 11:38:00 CST 2004

Scott,
 I am very interested in your pressure sensors. Do you have a schematic
for the control circiut? Is there a more reliable way than using a 555
timer? You mentioned a PIC processor, do you still have the code?
-Dan Gates



--- "SOLID Corp." <SOLIDCorp at ameritech.net> wrote:
> Hi David, I was working on a very similar biped project about 5 years
> ago
> but got distracted with other projects and never got to the really
> interesting stuff.  I did construct it using servos and had made a
> very
> accurate sensitive cheap pressure sensor for the bottoms of the feet.
>  Each
> foot had 4 sensors, one in each corner.
> 
> The sensors are each two pieces of 1 inch square unetched PCB, placed
> face
> to face, separated by a sheet of notebook paper, held together with
> electrical tape.  Each piece had a "tab" for an electrical connection
> that
> would not overlap the tab of the other board.  It is important that
> the
> boards be perfectly flat with no solder or anything to push them
> apart, I
> even dremmeled a bevel on the edges of the boards.  It is equally
> important
> that the paper cover the entire surface of the device so that there
> is no
> possibility of shorting.  I used it as a pressure sensitive capacitor
> in a
> ne555 timer circuit and measured the pulse widths for all 8 sensors
> with a
> dedicated 16F84 that was a serial slave to the main CPU.  It worked
> great,
> it was sensitive enough to count the number of quarters stacked on
> the
> device, it had a huge nonlinear dynamic range and the plates were
> large
> enough and close enough to each other that they were not noticeably
> affected
> by the proximity of people or metal surfaces.
> 
> The electrical tape was not the most durable material, I would try to
> heat
> shrink tube the whole thing now.  I tried rubber bands but they
> constantly
> compressed the sensor reducing it's lower range sensitivity.  A thin
> double
> sticky tape between the plates may work nice but it may be less
> flexible or
> interfere with the capacitance.
> 
> Anyway, good luck, I hope this helps someone,
> 
> Scott Williamson
> 
> 
> 
> 
> 
> 
> David,
>  I'm working on the foot sensors right now, there will be 4 digital
> (on/off) sensors in each foot. One for each corner to let the robot
> know when the foot is firmly planted. Analog pressure sensors would
> be
> nice, but I haven't found anything reasonable yet.
>  Next I will be figuring out where to install the two piezo gyros,
> I've
> been doing a lot of research on ZMP and ballance. One gyro for side
> to
> side ballance and one for front to back ballance.
> -Dan Gates
> 
> 
> 
> 
> --- "David P. Anderson" <dpa at io.isem.smu.edu> wrote:
> > Hey Dan,
> >
> > That explains it.  Maybe Mike's name _is_ mentioned and I just
> > overlooked it.
> >
> > What sort of sensors are you installing?
> >
> > dpa
> >
> >
> >
> > > David,
> > >  The Nuts & Volts article was not authored by me, I guess there
> was
> > a
> > > mixup somewhere down the line between submission and publishing.
> I
> > was
> > > asked to write the article, but my writing skills are severely
> > wanting.
> > > The credit goes to Mike Keesling, another fellow robot builder
> and
> > > frequent writer for N&V as well as the new Servo mag. Mike and I
> > worked
> > > together to make this initial article more of an inspiration to
> > others
> > > than a "How to".
> > > SAMM is far from complete and hardly ready for an in-depth "How
> To"
> > > type article. As you mentioned, I do NOT have ballance and
> > locamotion
> > > issues resolved yet. I think that error boils down to an editor
> > issue
> > > since I know that the submitted work does not mention it.
> > > I still have not seen the published version so I don't know what
> > other
> > > errors may exist, but I'm sure there are more.
> > > It's kinda like the old game we used to play in grade school. I
> > wisper
> > > a message to one person who then whispers to the next and so on
> > around
> > > the circle and when that message is finally repeated at the end
> it
> > is
> > > completely different than what was originally said.
> > > I am currently, as we speek, adding some more sensors to deal
> with
> > the
> > > locamotion and ballance. I suspect that in two months I'll be
> ready
> > to
> > > report again about SAMMs progress.
> > > I am a little upset that N&V didn't clearify who the actual
> author
> > > was, I know that Mike worked hard to write the piece and credit
> is
> > due
> > > him. Hopefuly the followup article will correct this.
> > > -Dan Gates
> >
> >
> > _______________________________________________
> > DPRGlist mailing list
> > DPRGlist at dprg.org
> > http://nimon.ncc.com/mailman/listinfo/dprglist
> 
> 
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