Hi All, I have been reading your mails regarding "DRIP".=20
With reference to the cut and polished L.E.D. I was wondering if you are =
aware that flat L.E.D.s are available, I have found several of these in =
cellular telephone keypads for illumination purposes, my thought is if =
these are OK for your purpose it might save you some work. Just a =
thought !

Kind Regards=20
Steve
  ----- Original Message -----=20
  From: George Harris=20
  To: psn-l@.................
  Sent: Sunday, August 18, 2002 1:11 AM
  Subject: Re: DRIP (diamagnetically restored inverted pendulum)



    ----- Original Message -----=20
    From: ChrisAtUpw@..........
    To: psn-l@.................
    Sent: Friday, August 16, 2002 4:48 AM
    Subject: Re: DRIP (diamagnetically restored inverted pendulum)


    In a message dated 15/08/02, gjharris@............. writes:=20


      A very sensitive and inexpensive two axis sensor can be made as =
follows:=20

      Above the top surface of the pendulum, place an LED with the front =
surface=20
      flattened so that it become a point source about 1/4 inch above =
the surface.
      On the top surface cement a 6mm square mirror (stock H43866 from =
Edmund).=20
      On each of the four sides of the LED place small solar cells =
(stock 980-0150=20
      from allied) in such a position that each will be half illuminated =
by the LED.


    Hello George Harris,=20

         Nice to have some extra input! I am having a problem in =
visualising the optical layout you suggest and the orientation and =
position of the various components. Is the LED 'water clear' plastic or =
what, please? What size? Are they IR or visible?  =20
          When you cut the end off a plastic LED and polish the end, =
looking into it, you see a bright central square chip surrounded by a =
ring of light from the plastic case. Putting a mirror on the end just =
reflects most of the light back through the base.=20
          Is that any chance of a quick sketch / 'paint' drawing, =
please?=20

          Edmund optics seem to be at http://www.edmundoptics.com/  =
There is no response to H43866, but there is a 10 mm square surface =
mirror NT45-517 @..........
     =20
    Response By George***************8

    The LED I used was the small clear type.  I sandpapered the surface =
until it was
    very close to the LED, then used finer sandpaper and polishing =
compound (tooth
    paste works) until it was bright.  This LED was mounted on a small =
PC
    board above the top surface of the pendulum looking down.  The =
spacing should be approximately 1/4 inch above the mirror which was =
attached to the upper
    surface.  The mirror used was 6 mm square (1/4 inch).  The resulting =
reflection is=20
    approximately a 1/2 inch square at the surface of the PC board. If =
now small silicon photosensors are placed on the same board =
approximately 1/2 inch apart, they will each be illuminated on 1/2 of =
their surface when the mirror is centered. =20
    The sensors I used are about 3mm (1/8 inch) square and moung flat to =
the board.
      The photocells can be connected in parallel, plus to minus, on the =
opposite sides across the inputs to a low noise operational amplifier =
with about a megohm in the feedback.  The resulting output is very =
sensitive (nanometers) and linear.


         The photo output of LEDs varies exponentially with temperature =
and you get about a factor of five reduction in light output at a =
constant current if you increase the temperature from 0 C to 100 C. =
Since you can expect ambient changes of >10 C deg and the LEDs =
themselves can heat up considerably, the variations are significant. How =
do you stabilise the photo output please?=20

    Response**********

    Since the photocells are both half illuminated, the null is not =
sensitive to the
    output of the LED.  The changes in the LED ouput would only slightly =
effect the gain of the system.  Since I was using the sensor in a =
feedback mode to recenter
    the mass, this effect was minimal.  My system was in a heated area, =
so the=20
    LED output change was very small.

       Regards,=20

         Chris Chapman=20







Hi All, I have been reading your mails =
regarding=20
"DRIP". 
With reference to the cut and polished =
L.E.D. I was=20
wondering if you are aware that flat L.E.D.s are available, I have found =
several=20
of these in cellular telephone keypads for illumination purposes, my =
thought is=20
if these are OK for your purpose it might save you some work. Just a =
thought=20
!
 
Kind Regards 
Steve

  
----- Original Message ----- 
  From:=20
  George=20
  Harris 
  
To: psn-l@.............. 
  
Sent: Sunday, August 18, 2002 =
1:11=20
  AM
  
Subject: Re: DRIP =
(diamagnetically=20
  restored inverted pendulum)
  


  
 
  
    
----- Original Message ----- 
    From:=20
    ChrisAtUpw@....... 
    
To: psn-l@.............. 
    
Sent: Friday, August 16, 2002 =
4:48=20
    AM
    
Subject: Re: DRIP =
(diamagnetically=20
    restored inverted pendulum)
    

In a =
message dated=20
    15/08/02, gjharris@.............=20
    writes: 


    A very sensitive and inexpensive two axis sensor can =
be made=20
      as follows: 

Above the top surface of the pendulum, place =
an LED=20
      with the front surface 
flattened so that it become a point =
source=20
      about 1/4 inch above the surface.
    On the top surface cement a 6mm square mirror (stock =
H43866=20
      from Edmund). 
On each of the four sides of the LED place small =
solar=20
      cells (stock 980-0150 
from allied) in such a position that =
each will=20
      be half illuminated by the LED.
    


Hello George Harris, =


     Nice=20
    to have some extra input! I am having a problem in visualising the =
optical=20
    layout you suggest and the orientation and position of the various=20
    components. Is the LED 'water clear' plastic or what, please? What =
size? Are=20
    they IR or visible?   =

      When you=20
    cut the end off a plastic LED and polish the end, looking into it, =
you see a=20
    bright central square chip surrounded by a ring of light from the =
plastic=20
    case. Putting a mirror on the end just reflects most of the light =
back=20
    through the base. 
      Is that =
any chance=20
    of a quick sketch / 'paint' drawing, please?=20
    

      Edmund optics seem to be =
at=20
    http://www.edmundoptics.com/  There is no response to H43866, =
but there=20
    is a 10 mm square surface mirror NT45-517 @....... 
  
    
Response By George***************8
    
 
    
The LED I used was the small clear type.  I sandpapered =
the=20
    surface until it was
    
very close to the LED, then used finer sandpaper and polishing =
compound=20
    (tooth
    
paste works) until it was bright.  This LED was mounted on =
a small=20
    PC
    
board above the top surface of the pendulum looking down.  =
The=20
    spacing should be approximately 1/4 inch above the mirror which =
was=20
    attached to the upper
    
surface.  The mirror used was 6 mm square (1/4 =
inch).  The=20
    resulting reflection is 
    
approximately a 1/2 inch square at the surface of the PC =
board. If=20
    now small silicon photosensors are placed on the same board =
approximately=20
    1/2 inch apart, they will each be illuminated on 1/2 of their =
surface when=20
    the mirror is centered.  
The sensors I used are about 3mm =
(1/8=20
    inch) square and moung flat to the board.
    The photocells can be connected in parallel, plus to =
minus, on=20
      the opposite sides across the inputs to a low noise operational =
amplifier=20
      with about a megohm in the feedback.  The resulting output is =
very=20
      sensitive (nanometers) and linear.
    


     The photo output of LEDs =
varies=20
    exponentially with temperature and you get about a factor of five =
reduction=20
    in light output at a constant current if you increase the =
temperature from 0=20
    C to 100 C. Since you can expect ambient changes of >10 C deg and =
the=20
    LEDs themselves can heat up considerably, the variations are =
significant.=20
    How do you stabilise the photo output please? 

    
Response**********
    
 
    
Since the photocells are both half illuminated, the null =
is not=20
    sensitive to the
    
output of the LED.  The changes in the LED ouput would =
only=20
    slightly effect the gain of the system.  Since I was using the =
sensor=20
    in a feedback mode to recenter
    
the mass, this effect was minimal.  My system was in a =
heated=20
    area, so the 
    
LED output change was very small.
    

   Regards,=20
    

     Chris Chapman=20