I hope this isn't to many lines.
      It is easily sensative enough to tell whether a led is lit
or not.  We had to come up with a way to keep other light sources
from shining on the photocell.  Some leds are quite close
together and I need to know which one is on.  The solution was to
use a piece of heatshrink tubing, preferably black.  It should be
just the right diameter to slip over the photocell and about an
inch long.  Shrink one end down so that the piece of tubing is
funnel shaped.  With this piece of tubing slipped over the
photocell, you can put the small end right over the led in
question.

      The squawker can be built in almost any kind of enclosure.
It should be comfortable to hold in your hand.  The photocell
should be mounted on one end so that it can be easily pointed at
a light source.  Mine was built in an old tape recorder
microphone case.  We used the dynamic cartrige for the speaker
and the pause switch to turn the squawker off and on.  A standard
nine volt battery fits nicely where the microphone cord was to be
stored.  This microphone was off of an old Craig cassette
recorder which Jim happened to have around at the time.  You
probably won't be able to find one, but that will give you the
general idea.

      Parts are not at all critical.  Almost anything will work
for a speaker.  I have used standard eight ohm speakers and
dynamic microphone cartriges.  Just use whatever fits the box you
are building the squawker in.  You may have to play with the
value of the electrolitic that feeds audio to the speaker.

      Likewise, the photocell is not critical either.  I have
found some that work better than others, but a common radioshack
photocell or even a surplus photo transistor works fine.  I used
a ten K resister in series with the photocell in mine.  You may
want to experiment with this value depending on the photocell you
use.  With no resister, the pitch of my squawker went so high
that I could not hear it.  The more light the photocell sees, the
less resistance it has and the tone increases in frequency.  As
the light decreases, the resistance increases and the pitch
drops.  With the 10K resister in mine, I just can hear the tone
at its highest frequency.  If you turn on the squawker in total
darkness, it won't make a sound until it sees a little light to
get it started.
      IC1 is a common 555 timer chip.  I power mine with a
standard nine volt battery.  The circuit follows:

Pin one of the 555 goes to ground and to the negative of the
battery.  The positive terminal of the battery goes to a SPST
off-on switch.  The other side of this switch is B+.  Pin 2 is
bypassed to ground through a .01MFD capacitor.  Pin 2 also is
tied to pin 6.  Pin 6 goes through a 10K resister to one side of
the photocell.  Pin 3 goes to the positive of a 4.7 MFD
electrolitic capacitor.  The negative side of this capacitor goes
to one side of the speaker and the other side of the speaker is
grounded.  Pin 4 is pulled high by going through a 10K resister
to B+.  Pin five is not used.  Pin 7 goes to the other side of
the photocell and also through a 22K resister to Pin 8.  Pin 8
goes to b+.


      That is all there is to it.  You might want to wire a closed
circuit phonejack across the photocell so that when a cable is
plugged into it, the squawker's photocell is taken out of the
circuit.  If you use a metal enclosure, insolate the jack so that
neither side is grounded.  You now have a light detecter or a
continuity tester.

73
Butch
WA0VJR
Node 3148
Wallace, ks.