[Laser] Ramsey transmit to CdS

[laser@mailman.qth.net]

Thanks John

If I did not make it clear before, I had used the CdS sensor on some 
experiments a long while ago.  The transmitter for that was a laser pointer driven by 
a 555 oscillator at about 700 Hz.  I had previously demonstrated that the 
Ramsey LBC6 receiver will pick that signal up very well.  I just wanted to check 
the other arrangement.

On the other hand: Since a CdS sensor can be used in a bright room to detect 
voice modulation on a light beam, it could be used in a classroom 
demonstration.  They are cheap and easy to get.  I dare say that a 5th grade science class 
will not appreciate the significant advantages of a photodiode.

I was not aware that CdS had slower frequency response in low light levels.  
My previous experiment would have suggested that the reverse is true.  Can you 
explain why?

James
N5GUI



CdS cells are a poor choice for detecting modulation. They are slow, and the 
lower the
light level, the slower the reponse.

IMO, you'd be much better off with a photodiode, back biased to reduce the 
capacitance
of the diode (space charge layer) and an optical BP filter.

-John