[sdiy] diy frequency counter

[Dave Manley]

David M. Ingebretsen wrote:
> As a teenager in the 70's, my brother and I bought a He-Ne laser to 
> play around with holograms. An electronics whiz friend of ours added a 
> audio modulation input to it. We took the laser a couple of miles 
> away, pointed it back at the house, set up a telescope, fed it into a 
> solar cell and pulled the audio back out. Very cool for a bunch of 
> teenagers...
>
> David.
I had no money for a laser!  The circuit I had basically took an amp 
with a transformer coupled output, put a resistor, battery and the bulb 
in series where the speaker would go.  It was crude, but it worked 
fine.  I had a pair of head phones with another amp and the solar cell 
as receiver.  In a dark location it was good for over a hundred feet.  
Of course, it suffered miserably from AC hum from any interfering light 
sources.

The wacky things kids used to do before video games. :-p

-Dave