From: scientist77017@gmail.com   
      
   On Saturday, May 18, 2019 at 4:28:40 PM UTC-5, default wrote:   
   > On Sat, 18 May 2019 11:51:26 -0700 (PDT), AK   
   >  wrote:   
   >    
   > >On Saturday, May 18, 2019 at 1:03:05 PM UTC-5, Cursitor Doom wrote:   
   > >> On Sat, 18 May 2019 10:50:16 -0700, AK wrote:   
   > >>    
   > >> > So it looks like even with a laser shining and someone breaks the beam,   
   > >> > it may not sound if the light level is high enough.   
   > >>    
   > >> Dump the LDR and use a photodiode instead.   
   > >>    
   > >>    
   > >>    
   > >>    
   > >>    
   > >> --    
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   > >   
   > >Would this work?   
   > >   
   > >Silicon Photodiode with Daylight Filter   
   > >PIN Photodiode Chip, BPW34   
   > >Features   
   > >Photocurrent: 80 µA (? 50 µA)   
   > >Reverse voltage: 32V   
   > >Forward voltage @ current: 1.3V @ 80uA   
   > >Total power dissipation: 150mW   
   > >Spectral sensitivity: 0.62 A/W   
   > >Wavelength of max. sensitivity: 850nm   
   > >Radiant sensitive area: 7.0mm²   
   > >Half angle: ±60 degrees   
   > >Short switching time: 20ns typ.   
   >    
   > You might try adding a potentiometer so you can adjust the   
   > sensitivity, then take some time and effort and install the detector   
   > in a light-tight tube with a  non-reflective black inside coating, and   
   > position the detector so the only light it sees is the emitter (laser   
   > in this case).   
   >    
   > 6' should be doable even with your simple system.     
   >    
   > You are using a laser for a light source.  It should work the way it   
   > is, but if you think about it, wouldn't it make more sense to use a   
   > narrow very bright laser beam on a small area like a photodiode or   
   > photo-transistor?   Concentrate the light on a small target then any   
   > extraneous light will be much weaker by comparison.   
      
   I put it in a 3 inch tube.   
      
   It worked but then it was overcast.   
      
   I will try again when I have full sun.   
      
   The photo diode might work as I can adjust the laser beam to be wider.   
      
   Andy   
      
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