>>>READER-TO-READER QUESTIONS AND ANSWERS
>>> ANSWERS
[#5083 - May 2008]
Has anyone hacked a digital
camera and installed the sensor and
minimum circuits into an old film
camera like an old Nikon F or Leica M2
or M3? I've seen astrophotog guys hack
a digital Canon EOS D30 and Rebel to
remove the IR filter for IR photography
... I don't know which electronics I can
safely clip out of the digital donor.
(There are film camera nuts out there
that would die to see this done.)
I’ve had little success taking apart
digital cameras. I’m on my third (since
2001) and once they break I’ve tried
to open the case out of curiosity. The
internal circuits are tightly packed and
use a lot of custom components that
would be hard to use again.
A 35 mm mechanical film camera
uses film at the lens focal plane to capture an image of 36 x 24 mm as
described here: http://tinyurl.com/
ygss4j. However, the active imager in
a digital camera is much smaller,
typically 4 mm to 16 mm diagonal,
as indicated here: http://tinyurl.com/
yx6q3s. Some form of relay lens
would be required to convert the 35
mm size image to that of the salvaged
sensor. This would not readily fit into
the existing film camera outline, and
would require access to precision
machine tools for construction and
alignment.
A brief history and description of
digital camera resolution is given here:
http://tinyurl.com/4j65sz. Overall,
your project is not practical, but
the digital camera technology is quite
fascinating!
Peter Stonard
Campbell, CA
[#6082 - May 2008]
Several years ago, I'd seen a device
that plugged into a laptop's modem
port and then to the headset port of a
cell phone, and presto — an Internet
connection! All that I can figure out is
the interface device must have
somehow produced a tone for the
modem to believe it had a live line.
From there, it was a simple matter of
pushing 'speed dial' on the cell phone
and away you went — surfing. Do you
have any ideas about this and how it
could be built from scratch? Better yet,
could there be something built that
would handshake between the data or
USB port?
What you are looking for is simply
a cellular capable modem, which can
be installed in parallel to your existing
modem if it is not cellular ready. I used
an IBM P/N 85H8059 FRU 38H5062
PCMCIA data/fax modem card on an
older laptop which was cellular
capable, but you need an adapter
cable for the specific cell phone. You
should be able to pick one up used
or surplus for very little money. Look
for Cellular Ready ("Spectrum
Connected") on the back of the
modem card. You will also need a
PCMCIA port on your computer. It
had a max speed of 33. 6 kbps, but I
think there was also a faster, later one
at 56 kbps from IBM.
Walter Heissenberger
Hancock, NH
[#7081 - July 2008]
My furnace/air conditioning
servicer recently replaced the control
unit in my high-efficiency furnace. The
defective portion of the control unit
turned out to be the spark generator,
but, in the process I see the unit has a
single-wire electric flame sensor, not
the old standard thermocouple. I can't
figure out how the thing works.
Can someone please enlighten this
old-timer?
In the old days of gas heating
appliances, a pilot flame was used to
start the main burners when heat was
required. Typically, this pilot was started by a match or a spark generator. A
thermocouple was used to check for
the presence of the pilot flame by
detecting its heat. If the thermocouple
failed or did not detect heat, the main
burners would not fire.
In today's energy conscious times,
standing a pilot 24/7 to light the main
burners is a waste of fuel. To save
energy, appliance manufacturers now
wait for a demand for heat, light the
pilot flame, check for a pilot flame,
and then open the main burner valves.
Some schemes don't have pilots and
directly spark the main burners. In
either case, detection of a good flame
is the key to safe burner control.
The single wire detection method
is viable because a flame acts like a
diode electrically. By expressing low
voltage AC across the sense wire and
detecting half wave rectification, the
ignition module can deduce the
presence of a good flame. Some
ignition modules use the high voltage
spark wire as the sense wire thus
eliminating the need for a separate
flame sense wire. The secret here is
the flame is a diode. No flame,
no diode, no rectification, no heat,
and hopefully no raw gas vapor in
your cellar.
John P. Gardner
Franklin, NH
[#7082 - July 2008]
Can a security system be built that
would utilize a switch on a door to
trigger a cell phone to call a number?
A similar system on the Internet costs
around $300. Can something be built
for less than $100 with a “pay as you
go” wireless phone?
Cellular phone electronics can be
purchased as modules, for “m2m”
(machine to machine) links over the
cellular phone network which allows
construction of hobby projects. For
example, the GM862 made by Telit
and sold through SparkFun Electronics
( www.sparkfun.com).
A GSM SIM card is required to
activate the phone which uses AT style
modem commands for control and
will send and receive data streams,
SMS text, voice, or data up to 57. 6
kbps. The module is compatible with
standard international GSM cellular
phone bands and SIM carriers in the
USA (AT&T, Cingular, and T-Mobile).
For a switch closure activated alarm,
the GM862 will only need a simple
microcontroller and a power supply.
The module sells for about $150.
Peter Stonard
Campbell, CA
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September 2008 95