webcam app to watch for and time stamp changes
Don't get hung up on the display EMI (for it is indeed very very tiny), look for
any steady emission. Yes, the amount is small, yes it can be shielded a bit,
but yes it is certainly possible to pick up. As I mentioned in my original
post, you may very well need to shield out external noise to see it clearly.
And with a not-so-sensitive analyzer, you'll need a pre-amp. Everything
electronic emits and is detectable unless it is shielded eight ways to Sunday.
Peter
On 3/3/2013 7:11 AM, Magnus Danielson wrote:
On 03/03/2013 10:00 AM, Poul-Henning Kamp wrote:
Content-Type: text/plain; charset=ISO-8859-1
In message657D7F7CC03849419A2A90752E6A60A6@pc52, "Tom Van Baak" writes:
When playing with watches a while ago I tried to pick up any 32
kHz signal but failed. Those with 1 Hz stepper motors were easy,
but LED or LCD displays were too electro/magnetic/acoustic quiet
for me to ever detect anything.
Most LCD and LED clocks have a shielding metal-coating on the front
glass, exactly to eliminate all EMI/EMC issues.
Darn. I should have guessed.
Cheers,
Magnus
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When LCD wristwatches became common in the seventies we, in the
frequency and timing group of a space tracking facility, investigated
the possibility of adjusting our new watches against our standard.
We found that a a small copper plate, about 1 X 2 cm, resting against
the display and connected to a scope probe was able to pick up enough 32
KHz energy to be displayed in the scope. Then connected the vertical
output to an HP 5245L counter referenced to our standard and set the
gate time to 10 seconds and got the frequency. We learned that the
watch had to be worn in order to operate at the right temperature, the
body acting as an oven, so you has to wear it backside in order to
access the trimmer (yes, at that time those watches had and adjusting
trimmer, maybe heritage from the mechanical ones, laser trimming arrived
later).
Our group became very popular and busy adjusting every watch our
colleagues bought to a few seconds per month.
Ignacio, EB4APL
On 03/03/2013 16:29, Magnus Danielson wrote:
On 03/03/2013 03:46 PM, Jim Lux wrote:
On 3/3/13 1:00 AM, Poul-Henning Kamp wrote:
Content-Type: text/plain; charset=ISO-8859-1
In message 657D7F7CC03849419A2A90752E6A60A6@pc52, "Tom Van Baak"
writes:
When playing with watches a while ago I tried to pick up any 32
kHz signal but failed. Those with 1 Hz stepper motors were easy,
but LED or LCD displays were too electro/magnetic/acoustic quiet
for me to ever detect anything.
Most LCD and LED clocks have a shielding metal-coating on the front
glass, exactly to eliminate all EMI/EMC issues.
Yes, but perhaps there's enough leakage to make this work. After all,
the EMI requirement (assuming it's running at 32 kHz) isn't particularly
stringent and because the fob is small, the radiated field at any
distance is going to very small. OTOH, I can put a probe or coil right
on or around the fob.
I'll let you all know what I detect when I try it tomorrow.
An electrostatic shield will not contain the H-field from the shifting
currents.
Cheers,
Magnus
On 3/3/13 9:12 AM, EB4APL wrote:
When LCD wristwatches became common in the seventies we, in the
frequency and timing group of a space tracking facility, investigated
the possibility of adjusting our new watches against our standard.
We found that a a small copper plate, about 1 X 2 cm, resting against
the display and connected to a scope probe was able to pick up enough 32
KHz energy to be displayed in the scope. Then connected the vertical
output to an HP 5245L counter referenced to our standard and set the
gate time to 10 seconds and got the frequency. We learned that the
watch had to be worn in order to operate at the right temperature, the
body acting as an oven, so you has to wear it backside in order to
access the trimmer (yes, at that time those watches had and adjusting
trimmer, maybe heritage from the mechanical ones, laser trimming arrived
later).
Our group became very popular and busy adjusting every watch our
colleagues bought to a few seconds per month.
yes.. adjusting your watch to a Hydrogen Maser.. there's a time-nut-y
activity...
On Sun, Mar 3, 2013 at 12:10 AM, Tom Van Baak tvb@leapsecond.com wrote:
Do you have suggestions on what sort of "antenna" to use to pick up the LCD AC E-field? I'd expect the LCD drive current to be vanishing small.
Many turns of fine magnet wire going all the way around the device.
Chris Albertson
Redondo Beach, California
On 3/3/13 8:52 AM, cfo wrote:
On Sat, 02 Mar 2013 11:33:02 -0800, Jim Lux wrote:
I am interested in the timing behavior of my RSA fob, which changes
every 60 seconds. Since I'm not about to open it up and probe inside, I
was wondering if someone had a clever way, say using a USB web cam, to
log the changes over a 48 hour period. You'd point the web cam at the
fob, and it would log the time when the display changes Or one might
even be able to look at the blinking 1 pps indicator using a light and
photocell or something..
Isn't this "Just what the doctor ordered"
http://smallhacks.wordpress.com/2012/11/11/reading-codes-from-rsa-
secureid-token/
Yes, basically..
Of course, installing your token permanently (as shown in the article)
kind of defeats the purpose, since the idea of two factor authentication
is "something you know" (the PIN/password) and "something you have"
(the token). If you don't keep physical possession of the token, that's
a big problem.
In fact, the article is all about getting around having the human
there.. the PIN is entered by his software and his software reads the
token. So anyone who has access to his computer has access to his
identity. And I'll bet his computer is connected to the internet, so
that means everyone has access to whatever is secured by his token.
(after all he is doing it so he can get access to his work VPN).
Probably a good reason not to use NetArt Group s.r.o. in the Czech
republic (his employer) if you care about security.
I suppose, though, there are places that are more casual. After all,
there's that guy who outsourced his work to China and mailed the guy in
China his token.
On 03/03/2013 06:18 PM, Chris Albertson wrote:
On Sun, Mar 3, 2013 at 12:10 AM, Tom Van Baaktvb@leapsecond.com wrote:
Do you have suggestions on what sort of "antenna" to use to pick up the LCD AC E-field? I'd expect the LCD drive current to be vanishing small.
Many turns of fine magnet wire going all the way around the device.
As a E-field antenna that's not that good, as you need to see both
polarities. Tossing a wire around like that would sense a little too
much of both, so it will cancel out.
A typical E-field antenna is a coax cable, stripped of wire, possibly
with a ball attached to increase the area.
H-field can make use of one or more loops before reaching the ground.
The near-field H-probe is two loops, wired such that long-distanced
fields cancels, but high-gradient fields is picked up. You should be
able to do the same for E-field, essentially three fields, with the
outer two being hooked to ground and the middle one to amp.
Cheers,
Magnus
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In message 51336234.3090105@earthlink.net, Jim Lux writes:
Most LCD and LED clocks have a shielding metal-coating on the front
glass, exactly to eliminate all EMI/EMC issues.
Yes, but perhaps there's enough leakage to make this work.
Think for a moment about how little power the electronics consume
in the first place, then do the math.
You'll need a very (radio-)quiet place to measure in...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On 3/3/13 10:09 AM, Poul-Henning Kamp wrote:
Content-Type: text/plain; charset=ISO-8859-1
In message 51336234.3090105@earthlink.net, Jim Lux writes:
Most LCD and LED clocks have a shielding metal-coating on the front
glass, exactly to eliminate all EMI/EMC issues.
Yes, but perhaps there's enough leakage to make this work.
Think for a moment about how little power the electronics consume
in the first place, then do the math.
You'll need a very (radio-)quiet place to measure in...
Not so oddly, I happen to have such places available, since we develop
sensitive radio receivers and instruments for deep space. I don't know
how well shielded from a magnetic field standpoint our usual screen
rooms are (probably not very.. they're all designed for 2GHz and up),
but it's easy to try.
I also know someone who has a set of nested mu metal cans for this kind
of thing that I might be able to borrow.
We used them to calibrate little hockey puck shaped spinning
magnetometer subsatellites for a sounding rocket experiment:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17005/1/99-0421.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17761/1/99-1204.pdf
It's not an e-field antenna. The goal is the sense the current in the LCD.
My bet is no much of anything leaks out of that RSA device or a wrist
watch either. You have to figure that tiny battery lasts for over a
year and even if ALL the energy in the battery went to making RF you'd
divide the battery energy by the battery life time to get power.
What's have some micro watts at most. Then you figure most of the
bettery power really goes into heat not RF.
As a E-field antenna that's not that good...
Chris Albertson
Redondo Beach, California
On 3/3/13 10:47 AM, Chris Albertson wrote:
It's not an e-field antenna. The goal is the sense the current in the LCD.
My bet is no much of anything leaks out of that RSA device or a wrist
watch either. You have to figure that tiny battery lasts for over a
year and even if ALL the energy in the battery went to making RF you'd
divide the battery energy by the battery life time to get power.
What's have some micro watts at most. Then you figure most of the
bettery power really goes into heat not RF.
detecting femtowatts isn't really an issue for RF.. 1 fW is -120dBm,
which is a "strong" signal in a lot of applications. Typical FM
receivers have sensitivities around 0.2 microvolt into 50ohms, which is
about a femtowatt. -150dBm is getting tougher, but is still 24 dB
above the kTB noise floor in a 1 Hz BW.
However, what we're looking for here is most likely a changing magnetic
field. It's not being "radiated" away, the energy stays in the circuit
(in the near field) for the most part. (question, does putting a RSA
fob in a lossy magnetic medium make the battery go dead faster?)
So the question really comes down to how small a repetitive change in
magnetic field can be detected?
Or if you're using an efield probe, it's sort of the same thing. You're
not concerned about far field radiation, which will be very small (the
"antenna" is a tiny fraction of a wavelength.
Here's a similar thing.. Say you have a twisted pair carrying a signal:
very little radiates away. But if you have a small probe (E or H) you
can put it closer to one wire of the pair than the other, and
(potentially) detect the E or H field from the wire.