Alt-BEAM Archive

Message #05538



To: beam@sgiblab.sgi.com
From: Wouter Brok w.j.m.brok@stud.tue.nl
Date: Thu, 05 Aug 1999 12:58:14 +0200
Subject: [alt-beam] Re: HEAD MECHANISM(LDR)


Hello Jason.

Yes, you can use LDR's in a bicore head (I think that's what you mean,
don't you?) The idea with the two photodiodes in the bicore is that the
resistance one way is different from the resistance the other way so to
say. Like this the duty-cycle of the output block-waveform of the bicore is
different from 50% dependent on the relative amount of light falling on the
different photodiodes. If you want to do a thing like that with LDR's you
have to make something up so that with these parts as well the resistance
is dependent on the direction of the current. The ideal part for doing a
thing like that are diodes: on way they have infinite resistance, the other
way less (it is a bit more complicated because of the 0.6V voltage across
the diode, but you can leave that out to understand the general principle.
If you experiment a bit you will see). So what should you do? put a ldr in
series with a diode. and another ldr in series with another diode and put
the things you made (ldr in series with diode) in parallel with eachother,
so that the diodes are 'pointing' different ways (don't know how I can say
that properly). Like this the current one way has to choose its way through
one side of the circuit, through one ldr and the current the other way has
to choose the other side of the circuit. Hope you understand what I mean.

---------|>|-------/\/\/\-----------------
| |
-----|<|-------\/\/\/------

Instead of the resistor in a normal suspended bicore

\/\/\/ is ldr
|<| is diode

This is my first ascii drawing and it doesn't look like anything, but maybe
it makes it a least a bit more clear what I mean.

Note that I didn't try this; just made it up right now, so there are
probably betters solutions around, but I'm sure you will hear about them
later, from other people.

Regards,

Wouter Brok.


>Hie i would really like to know how build a head using two LDR instead of
>photodiodes which i already did for my 2DOF heaad which can only track a
>torch light but i heard darrel johnson said an LDR is even better cause it
>can track bright objects too like the power smart head....and i heard
>someone said it in the list before or maybe in the beam tek faq that a bot
>using servo as motor cant be solarized,.,...then can someone explain to me
>how dave solarrized his sunseeker head mechanism..cause i really want to do
>that too...thanks a lot everyone
>
>jason
>
>
>______________________________________________________
>


5539 Wed, 4 Aug 1999 13:29:21 -0500 [alt-beam] junk mail about free touch sensor , "cbrenizer" haven't checked this out past viewing their home page.

Anyone have any experience 'hacking' resistive sensors like this? are th=
ey
the type of element that can be cut into strips and still function?

a thin strip wrapped around a 'bot's perimeter could indicate the directi=
on
of a touch or object via the varied resistance...


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i bet 'bending' or wrapping the element around a round 'bot interferes wi=
th
any useful readings, but multi-facetted perimeters as an octagonal or
hexagonal design may be able to incorporate this.

opcode joe
=DE-:
opcodejoe@mail.trib.net
ICQ# 11118760

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