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down. I have scoped the in and out,
but there is no activity.
If the processor is dead, then a
$1,500 item is junk, unless someone
I would like to have a schematic,
service manual, literature, or advise.
My FM Radio Hates My New
High Output Fluorescent Lighting
I have installed some 8' HO
fluorescent lights, and now the FM
radio has too much noise.
I put four snap-on RF chokes on
the power cord at the radio. They did
reduce some of the interference and
I even plugged the line into a surge
Is there anything I can do at the
fixtures to knock out this RF problem?
#9129 David Robin
Wireless Water Level
I'm looking for a schematic
solution to wirelessly indicate the
water level of a distant water tank
more than 100 m away.
[#7124 - July 2012]
Garage Door Sensor
What’s the best way to hack the
garage door sensor so that when the
garage door is open, anything breaking
the light beam will trip a relay?
#1 This will vary from one garage
door opener to another, but most that
I've seen have an LED either on the
photo beam receiver or on the opener
itself that illuminates when the beam is
intact. If I wanted a relay to trigger, I
would tap into this LED. If you want to
interface to it without modifying
anything, a phototransistor or CdS cell
could be mounted over it to detect
light from the LED. Anything else will
require some reverse engineering on
your particular opener.
#2 I did something similar with a
toy called "Laser Shot" that was sold by
RadioShack years ago.
I wanted the target to flip a relay. I
used an astable multivibrator circuit —
I believe I used the 555 timer to a
7400 series counter, which then drove
a transistor, which held the relay on
In any event, you need to poke
around until you find anyplace where
the voltage changes when the light
beam is broken. Then, you take that
voltage and clean it up for your circuit
I used the 555 in astable mode. It
would trip into the unstable voltage,
wait for some time, then flip back to
the stable state. (This may not work for
something blocking your light beam,
depending on what you want your
circuit to do when the beam is continually blocked.) The Laser Shot had a
measurable time it was making noise,
or time the circuit would trigger the
noise generator. All I had to do was
get a clean pulse from the 555 to a
counter circuit, where the lowest bit
was used to drive the transistor which
then held the relay open or closed.
Your circuit may be simpler. You
may only want the relay to flip when
the beam is broken and then flip back
once the beam path is cleared. You
[#7125 - July 2012]
CCD/CMOS Camera Back
One of my deepest desires has
been to "resurrect" my film cameras as
digital. Is it at all feasible to construct
some sort of relatively compact and
usable CMOS or CCD device which
can be attached to an existing camera
that would yield high resolution
images to be stored on a standard
memory card? If so, could a diagram
and list of materials be provided?
I would prefer a full format sensor for
use on a full format 35 mm camera, but
a smaller format sensor would
be acceptable for attachment to microscopes or telescopes.
The biggest issue with what you
would like to do is that typical CCD
sensors are a fraction of the size of a
35 mm film frame. In order for the
existing optics to focus properly onto
the sensor, it has to be located in the
same plane the film would be. If you
install a 1/3 inch CCD in a 35 mm film
camera, you will only be capturing a
small portion of the field of view.
Anything is possible with enough
effort, but given the low price of some
very good digital cameras these days,
you are better off buying one than
trying to convert something and
ending up with inferior results.
[#7126 - July 2012]
Schematics and Components
I don’t know that much about
reading circuit diagrams, but in theory,
if I bought all the components in a
given diagram, could I simply connect
each component to the others as
shown in the schematic? I have seen
references to using a breadboard but
from what little I’ve read, they are
configured in various ways and I
wouldn’t know what configuration a
given project might require.
I understand that soldering
component leads together with no
substructure or framework might look
like a piece of modern art, but could I
do that and expect it to do what it is
supposed to — whatever that is?
September 2012 79