On 1/1/2013 7:48 PM, Tangazazen@....... wrote:
> Hi Geoff,
> With regard to photo resistors, Chris is right they are not really 
> suitable. A silicon  optical sensor is very flexible. If you want to 
> eliminate flicker noise altogether then modulate an LED light source 
> at say 5Kc/s where it is free of flicker noise and then use a phase 
> sensitive rectifier. The effective noise bandwidth is then the 
> reciprocal of a quarter of the phase sensitive rectifier time 
> constant. This is the technique I us on the orthogonal  seismic 
> sensor. Take it one step further by fitting a magnetic force unit and 
> close the loop and you have a broadband system whose lower frequency 
> response is set by the feedback network.
> Martin
Are you saying I should use a modulated method for the LED,
instead of a steady current source ?
I was thinking like a very narrow range for full light to
no light on the photocell. Like incline the photocell
at a shallow angle or something similar ??
Swing the Photocell or LED from a pendulum ?
Use an aperture of some kind to occlude the light ?
Use a silvered surfaced mirror like the real scientist might use ?
I generally do not modulate anything.
The only AC signal being the motion itself. Amplitude modulated light ?
Regards,
geoff


  
    
  
  
    
On 1/1/2013 7:48 PM, Tangazazen@.......
      wrote:

    
    

      
      
      
        
Hi Geoff,
        
 
        
With regard to photo resistors, Chris is right they are not
          really suitable. A silicon  optical sensor is very flexible.
          If you want to eliminate flicker noise altogether then
          modulate an LED light source at say 5Kc/s where it is free of
          flicker noise and then use a phase sensitive rectifier. The
          effective noise bandwidth is then the reciprocal of a quarter
          of the phase sensitive rectifier time constant. This is the
          technique I us on the orthogonal  seismic sensor. Take it one
          step further by fitting a magnetic force unit and close the
          loop and you have a broadband system whose lower frequency
          response is set by the feedback network.

        
        
 
        
Martin
      
    
    Are you saying I should use a modulated method for the LED,

    instead of a steady current source ?

    I was thinking like a very narrow range for full light to

    no light on the photocell. Like incline the photocell

    at a shallow angle or something similar ??

    Swing the Photocell or LED from a pendulum ?

    Use an aperture of some kind to occlude the light ?

    Use a silvered surfaced mirror like the real scientist might use ?

    I generally do not modulate anything.

    The only AC signal being the motion itself. Amplitude modulated
    light ?

    Regards,

    geoff