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[Brian H]

No problem. I was thinking an inverting
transistor or a simmilar circuit myself. See
what I can do.

[iceblue]

Brian H....thanks...here's a linkl to a
wesite which shows a circuit diagram (near
the bottom of the page) for LDRs and
transistors.  Also, there are links for
sizing transistors.  Even though I have read
it, along with many other similar websites,
I still can't translate it into an actual
project...I think I am electrically
challenged!

[iceblue]

The link:
http://www.kpsec.freeuk.com/trancirc.htm

[Brian H]

Ok gave it a look and will see what I think.
First impression is it may not work as the
transistor when ON to simulate the closed
switch normally used. It will have almost
zero voltage on it and turn off. Side note.
On a Google search I did find someone that
modifies the door window sensors for a
normally open contact that closed when
tripped. Also this mod costs you I believe
$79 for one modified module. I also kind of
remember reading the older original
dorr/window sensors had a jumper to pick
normally open or closed. Not in the newer
ones as far as I can see. X10 didn't release
the schematics of the sensor but I did find
the X10 made RS sensors schematic. If worse
comes to worse. I maybe able to do a mod on
that module; that will register with a
DS7000 console.

[iceblue]

Brian H...here is another response I
received from GBartlett at an EZBoard
(http://p199.ezboard.com/fbasicelectronicspro
jects.showMessage?topicID=889.topic)  This
shows how to modify the function of the
photocell: "...A better bet is to use a
circuit such as the one on this link:-

home.cogeco.ca/~rpaisley4...ctors.html

Replace the LED and resistor with the relay,
and you're sorted. Comparators are cheap.
The only problem would be connecting one up -
the catalogue you buy it from should
provide a datasheet or pinout for which pins
are + and - inputs, which pin is output, and
which pins are Vpwr and 0V. R1 should be a
variable resistor, so that you can tweak the
circuit to get the turn-on point just right.
There actually is a circuit on there for
doing this, so you should be OK. Graham."
What do you think?  Could you translate this
into a parts and to do list?  Thanks.

[Brian H]

Went there got the date. Hope to have
sommething for you.

[Brian H]

Will look at the Shack tomorrow. The LM339
shown in one of the diagrams your web page
showed. Has an open collector output. Plain
talk should toggele the sensors output no
relay needed. Will need its own small
battery pack or wall wart to work. Guess
batteries are better as AC goes off.

[Brian H]

Got the parts to test with. Now do you think
the detector we are trying to use will be in
normal [not bright] daylight. The photocells
change mostly from real dark to room light
than from room light to real bright smoke
detector light on. Can probably compensate
so only real bright light will trip it. The
photocells come in a kit of 5 and each is
different than the rest. I may use a mini
adjustable resistor to make it easier. 3
parts unused in the chip. Maybe an added
output to light an LED when the detector is
tripped? Feedback from you would help.

[Brian H]

Got the parts connected in an Experimenter
Bread Board and have started some tests. The
schematic on the web page for the cad cell
detector is close to what I found. It can be
done as shown, but each cad cell may need R1
hand selected or you can change the (2)10K
resistors and have a small adjustable
resistor to the + Input of the chip and use
a 1K for R1.
Not 100% on getting it on a PC Board today,
but maybe.
One of the unused 3 sections of the same
chip can be wired as a I see light and have
opened the signal to trip the Window/Door
sensor indication with an LED if wanted.

[iceblue]

Brian H....thanks for looking into this.  I
would like to use the First Alert smoke
detector model SA304.  This model has the
escape light (ultrabright LED).

[iceblue]

Beian H...my thought was to clear silicon
the photocell to the clear lens of the
Escape light and then paint any remaining
exposed part of the clear lens black so that
the photocell would be in total darkness
until an ALARM--which would cause the
ultrabright LED to light.

[Brian H]

OK that may make it even simpler. The
diagram as shown on the web page should do
fine with a large Black to Bright White
difference.

[Brian H]

iceblue; I have not forgotten you. Prototype
should be worked on today. If I can give you
values and pinouts for the chip is thet
enough?

[Brian H]

Iceblue;
Got the circuit tested and functional. Since
you
indicated you where going to have the cell
dark.
I did not add the adjustment variable
resistor and found
a R1 value that worked for all 5 Photocells
in the assortment.
I used the  Circuit #2 Cds Photocell Diagram
from  Rob Paisley.
IC1 LM339 RS#276-1712
PC1 Photocell RS#276-1657 Pack of 5
R1 2.2k 1/4W RS#271-1325 Pack of 5
(2) 10K  1/4W RS#271-1335 Pack of 5
14 pin IC socket optional RS#276-1999
I used a 6V supply from a 4 AAA cells in a
holder I had.
Led and Resistor not used on the output
IC Pin #3 + Power; Pin #12 Common; Pin# 7 +
Input  to 10K resistors;
Pin #6 -Input to cell and R1; Pin #1 Output
to Door/Window Sensor
Connect the + signal wire from the sensor to
Pin #1
Connect the - signal wire from the sensor to
common.
When the cell is dark the IC is ON and acts
like a closed switch
When it is brightly iluminated it turns OFF
it acts like an open
switch.

[avnish]

i had make an ldr based alrm in which i had
use a laser, transistor,resistance,capacitor
and speaker now i had to give project report
on it can you help me to give it and provide
me information about ldr,cpacitor,speaker.
and transistor please help me