Fluorescent Lights Magically Activates iMac? 108
bats asks: "In my computer room at home, I have several machines -- and a fluorescent desk lamp. Among my various boxen is an iMac DV (slot loading) circa 1999. Its configured to go into power saving mode, but respond to wake-on-lan packets. The weird thing is this: If I flip on the fluorescent desk lamp, the sleeping iMac will suddenly wake up! This happens with 100% consistency. The desk lamp is plugged into a power strip and into the wall. The iMac is plugged into a UPS and then into the wall. The network switch for the room is near the desk lamp (1-2 feet) but the iMac is some distance away (8-10 feet). My question is: WTF?! How the heck does the iMac know when the light comes on? It seems like it must be some power spike in the AC or noise on the network interface. However, the power strip and the UPS should block an AC spike and the chance of electrical noise in the cat-5 looking like a wake-on-lan packet seem more than miniscule. So again I ask you, dear AskSlashdot reader, WTF?! I await conspiracy theories, pseudo-science, wild rantings, and hopefully, the right answer."
Find the reason... (Score:2, Interesting)
If you find out its a WOL... make sure your neighbor isn't peeking through the window just to screw with ya!
Hmm. (Score:3, Funny)
Re:Hmm. (Score:2)
Re:Hmm. (Score:2)
Seriously, I agree with the other poster, that this is probably line noise on the cat5 cable. Some rearranging plugs, etc should be able to figure out what will cause it, what won't. May not get the explanation you want, but seems like you'd at least know "if the lamp is over there, it doesn't happen".
Cat-5 noise (Score:3, Informative)
Try putting more distance between the hub/switch and the light, and see if it still causes it to happen. I wouldn't imagine the light could cause much interference over more than a few feet or so. You might also try hooking up another machine, and monitoring all the electrical activity on the network. Myabe something will poke up.
Re:Cat-5 noise (Score:1)
Re:Cat-5 noise (Score:1)
Re:Cat-5 noise (Score:3, Interesting)
Shielded Cat-5. Ground loop? (Score:2, Informative)
Exactly true. Shielded Cat-5 is more expensive. It is more difficult to find a supplier. And, in this case, shielding would almost certainly not help. The noise is definitely not coming from some electromagnetic connection with one wire inside one of the twisted pairs.
The problem is probably a ground loop; probably the noise is being conducted along the ground wires. More directly grounding the components to each other may help.
Also, it seems to me that Wake-on-LAN is a technology that is usually not implemented well. I've seen cases where it was a selling point, but caused problems.
One thing that helps stop Cat-5 noise is grounding the unused four wires. There are 8 wires in Cat-5, and only four are normally used. (It is possible to buy adapters that allow one Cat-5 to carry Ethernet for two computers, but that is not normally done.) There is electrical capacitance between one Cat-5 pair and the others. When you ground the unused two pairs, you are grounding most of the common-mode noise that would otherwise be experienced on the two pairs that are used. In a low-noise environment like the one mentioned, grounding the unused wires would be the equivalent of having shielded Cat-5. This is something you can try without cost if the Ethernet signal travels through an accessible wall or other connector.
However, as I said, the problem sounds to me like noise conducted along the ground wires, a "ground loop".
Re:Shielded Cat-5. Ground loop? (Score:2)
The problem is probably a ground loop; probably the noise is being conducted along the ground wires. More directly grounding the components to each other may help.
It may just be my universe, but I don't ever recall coming across a grounded fluorescent lamp. That, and none of the wires in ethernet is ground... there's a differential TX pair and another differential RX pair, the rest being unconnected.
I would be willing to bet that it's a noise spike getting misinterpreted as a (bad) ethernet frame. UTP is generally pretty good at ignoring common mode noise but but without really getting into the details of the problem I can't say whether the noise really is common mode or just "almost" common-mode.
IMO WOL should only wake on a good packet destined for the MAC of the sleeping computer, but it appears that it's just another broken technology.
Bad ground. (Score:2)
Yes, but how is the noise signal getting into the computer? Generally, there is some problem with the ground. The noise from outside wags the entire computer around because of the bad ground.
If there is a bad ground, the noise on the ground side can overwhelm the common-mode capability of the differential pair.
E-mail message about noise on Ethernet: (Score:2)
Someone wrote the following e-mail message to me. I decided to remove his name and company, but post the messages, so that everyone could benefit.
______________________
G.T. wrote:
Just read your slahsdot posting on CAT5 cables. I am at the moment constructing an ethernet to fiber converter for long haul applications.
I have been looking at various application notes from different ethernet chip companies, and I have noticed that some (but not all) designers does just what you writes: they connect the unused ethernet pairs via a resistor to ground, and after reading your post I finally understood why
Soooo, where did you learn this? I have read (or browsed trough) the IEEE ethernet standards, and have not seen this anywhere. I believe that there are other tricks like this that I really should know. Do you know of any good resources for ethernet from a hardware point of view ?
Best regards
G.T.
____________________________________
G.,
I am happy to help. The attached information is very difficult to find on the internet. That's why I carefully saved it to PDF files. If you need more information, let me know.
My information about the likely causes of problems with noise comes from having been an electronics circuit design engineer. You would not use a resistor to ground the unused Ethernet pairs, that would defeat the purpose a little bit. You would ground them directly. You can ground two wires, one from each pair, at one end and the other two at the other end. You should not ground any wire at both ends, because there may be a voltage difference between the two grounds.
My experience with 100 BaseT Ethernet is that it is generally problem-free. That's what led me to suspect a problem with grounding. Something is overcoming the common mode noise rejection of the Ethernet receiver, I guessed. That is most likely to be a loose ground. For example, maybe the computer in the Slashdot example is not grounded at all. It could be that the outlet to which it is plugged has a bad ground connector. I would suspect something simple like that.
Often with ground problems, people have symptoms which cause them to look in the wrong place. Before I was a design engineer, I was a repair technician. I repaired aircraft automatic flight control systems. One day an aircraft came in with 4 very serious malfunctions. Partly lucky and partly smart, I said, hey, wait a minute. I don't believe 4 malfunctions happened in one flight. I began to look for one thing that could cause all 4 malfunctions. The only thing they had in common was the ground. I told the crew chief to look for a bad ground. They found that someone installing some equipment had not remembered to re-attach the ground to the entire bay of equipment.
Again, it seems reasonable to repeat that Ethernet and 100 BaseT are very well-designed, robust technologies. Anyone who has problems should suspect something simple. Shielding of the Cat-5 and grounding of the unused pairs is only necessary when the noise is extreme, such as when doing arc welding 1 foot away.
Regards,
Michael Jennings
Re:Cat-5 noise (Score:1)
FFFFFFFFFF
My-MAC-Add
My-MAC-Add
My
My-MAC-Add
My-MAC-Add
My-MAC-Add
and your mac might be responding to that
That would be one hell of a coincidence for your lamp to generate that packet! I'd get the ballast and tubes replaced.
Pi
For Great Justice|ecitsuJ taerG roF
logical process... (Score:5, Insightful)
Re:logical process... (Score:1)
But then he won't be able to reload slashdot and report his findings!!!!!
i had this problem once... (Score:5, Funny)
Easy fix (Score:4, Funny)
Does it have IR port? (Score:4, Interesting)
My PC turned on after any phone ring (very disturbing while installing some new hardware
BTW does you mac have external modem? Probably your modem tells RING each time you turn on the lamp. Easy to check with any terminal program.
Re:Does it have IR port? (Score:1)
I don't want to sound obvious, but, did you ever try unplugging the computer before installing new hardware?
Re:Does it have IR port? (Score:2)
Re:Does it have IR port? (Score:1)
correct me if I'm wrong, but.... (Score:1)
I could've sworn, (been a while, haven't needed to open any cases lately), that the green LED on the MB that is usually lit when the power is off, actually turns off when you flip the physical power switch on the power supply. It just takes a second or two for the LED to discharge the electricity from the capacitor.
First-gen ATX power supplies (Score:2)
It would appear that the ATX power supply predates the ATX power supply switch by about a year, depending on manufacturer.
A lot of those first-gen ATX power supplies had severe reliability problems as well (I've seen batches with %20+ failure rates after six months), so they're increasingly rare.
Re:Does it have IR port? (Score:2)
Re:Does it have IR port? (Score:2)
Don't know if his computer has an IR port, but it's pretty much guaranteed that most anything that puts out white light (everything between infra-red and ultra-violet) puts out some UV and IR as well.
Re:Does it have IR port? (Score:1)
It was sort-of useful, mostly fun though. Tape over that IR port and test it!
EMI (Score:2, Insightful)
Format of a Wake-On-Lan Frame (Score:5, Informative)
IBM has a White Paper, Wake up to Wake-on-Lan [ibm.com] which describes the specific format of a Wake-Up packet (6 bytes of F (XX'FF') followed by a 48-bit target address repeated at least 8 times). Even if the target address was a broadcast address, I don't see how this could be reliably generated by the starting of a fluorescent lamp. Plus, your average LAN has a whole bunch of traffic going on all the time anyway.
I have an iMac DV (graphite), and I DON'T have it plugged into a network, and it's NOT configured for Wake-on-Lan, nor is it configured to wake on phone rings, and I don't have any infrared devices that I know about, and I have an optical mouse, so it won't wake if the mouse gets moved, and it still wakes up when I vaccum my living room or turn on my slide projector.
Static discharge (Score:1)
Re:Format of a Wake-On-Lan Frame (Score:1)
"OK, look. If there are any voltage changes on the line, there's a 90 percent chance it's LAN activity. We'll have it wake up then. Hey, it's Wake On Lan, innit?"
Re:Format of a Wake-On-Lan Frame (Score:1)
Sounds like famous last words to me.
Re:Format of a Wake-On-Lan Frame (Score:1)
Obviously, iMacs get jealous whenever another electrical device in the room gets used. "*sniff* there he is, vaccuming again. Maybe if I turn myself on he'll come play with me."
Fluorescence (Score:1)
Anyway, Compact Fluorescent lights have been known to interfere [gelighting.com] with IR devices and radios. Like others have said, I would guess it's probably just putting out a lot of noise.
does it (Score:5, Funny)
Airport? (Score:2, Interesting)
Mobiles phones (Score:4, Interesting)
My guess is that one of the periodic cell checkin transmissions induced enough of a current in the on/off circuit that the metronome decided to switch on. Spooky!
--
mouse + light (Score:5, Insightful)
Try the experiment with the mouse covered up with a rug and switching the light on.
I had an experiance where at certain times of the day the mouse cursor would go a bit funny. took a while to work out it was when the sun peeped throught the window at just the right angle...
a rug?? (Score:1)
Re:a rug?? (Score:2)
I guess rug has slightly different meanings in different parts of the world. (over here we often just use it to mean a cover. eg: blanket or even a jumper / shirt eg: dont forget to rug up! meaning don't forget to put a jumper on its cold outside!)
Re:mouse + light (Score:1)
Re: (Score:2, Interesting)
Re:USB Desk Lamp (Score:2)
Re: (Score:1)
mouse (Score:1)
Even more weird: Flushing toilet can caouse reset (Score:2, Interesting)
It was one of those old style toilets whith a big water tank high above the seat and if you pulled the trigger a huge amount of water caused a "whoosh" that would have made Al Bundy happy...
I think I worked around the problem by stabilizing the reset line with a condensor or so. Then the power supply finally died, so I played with 6V batteries to power my C64 and one day accidently killed it somehow
I have no clear idea that the physics behind that was: Was it the same effect that made rising/falling raindrops cause thunders? Or did the quick movement of a large mass of (soemwhat) electric conductive material disturbed the electric field?
BTW: Switching on the light+fan in the toilet had no effect on the C64.
Re:Even more weird: Flushing toilet can caouse res (Score:1)
Re:Even more weird: Flushing toilet can cause rese (Score:1)
Re:Even more weird: Flushing toilet can caouse res (Score:2)
I think I worked around the problem by stabilizing the reset line with a condensor or so. Then the power supply finally died, so I played with 6V batteries to power my C64 and one day accidently killed it somehow :-(. IIRC the toilet has gone by now as well.
You'd have had to use more than 6V batteries to get your C64 to boot; the power supply provided both DC and AC voltage (5VDC and 11VAC IIRC) -- I had built a power supply from a small transformer and some small gel-cell batteries since I had no decent 78xx regulators on me.
Re:Even more weird: Flushing toilet can caouse res (Score:1)
(I didn't need the datasette and the RTCs were rarely used anyway).
But it depends on the models, later models didn't need the 9VAC at all and could operate on 5V only.
Re:Even more weird: Flushing toilet can caouse res (Score:2)
If you still had the thing, I'd say touch up the power supply PCB connections with a soldering pencil, or better, replace the 7805 3 pin voltage regulator at the same time.
Used to work at a company producing C-64 software way back when, I had to fix some of those beasties... the C-64 really wasn't intended to run 18+/7.
Re:Even more weird: Flushing toilet can caouse res (Score:1)
> toilet flushed, and that's probably why the power supply died as well, when the crack turned
> into a break.
That was certainly not the case - other vibrations or shocks (e.g. shutting the door, moving the chair to the desk, hitting run/stop-restore on the keyboard, footsteps) would have caused it as well - but that didn't happen.
The problem with the power supply was that it simply didn't provided the correct voltage. It was closer to 4V than to 5V.
> I'd guess but don't know that the brick was plugged into the wall on the side next to the toilet, right?
No, it wasn't. And further more: it was a brick wall, the power supply was on the floor, more closer to the opposite wall. Sadly, ASCII art is considered "lame" by slashdot's filtering system, so I can't provide a sketch from the room.
Disclaimer: This is all from memory since it was 13-15 years from now.
Your UPS is sending a heads up ... (Score:4, Interesting)
so that it can inform the machines
when there is a change of status of
power line? Maybe when the light is
turned on, the power surge makes UPS
send a packet to your network? Just
guessing.
Lamp + Ethernet (Score:3, Interesting)
Similar story... (Score:1)
Once we realized this, we had lots of fun tormenting each other by setting roommate #1's speakers all the way up and playing his CD at full volume while he was doing stuff. Nothing like hearing Jimi Hendrix's Band of Gypsies at max volume at 3 am!
sometimes they fool you... (Score:1)
The answer (Score:2, Informative)
The answer to your dillema is pretty straightforward: when you turn the light on, your *optical* mouse is noticing a change in the pattern on the desk, and interpreting this as the mouse being moved to wake the Mac.
The way to test this hypothisis 100%? Unplug the optical mouse, let the bugger go to sleep, and turn on the light.
Easy, neh?
P.S. It does that in a few of my setups (I work in the dark, with a Kensington Flylight over the keyboard usually) -- but the Apple optical mouse seems much more succeptible than my Logitech cordless optical. Chances are this is because the Apple mouse is mostly transparent.
Re:The answer (Score:1)
Another note: (slightly OT)
The principles of Okham's Razor [panikon.com] almost always apply to tech support and troubleshooting.
The simplest answer is, truly, almost always the correct answer -- or at the root of the problem.
You can also call it the Tao of Tech Support if that sounds more pleasing, but if you follow problems to their most glaringly obvious potential causes, you're normally on the path to getting the problem fixed with minimal, er, resistance (couldn't resist) and energy expenditure.
Re:The answer (Score:2)
Sometimes it is. William of Occam lived long enough ago that spelling was by no means standardized. There are at least three different spellings in use. You can find more about this with google.
Re:The answer (Score:2)
Well that would be a good answer... except that Mac's usually don't wake on mouse activity. For example, with every single mac in our office, wiggling the mouse does nothing. Hitting the shfit key is the prefered way to wake them up.
Re:The answer (Score:2)
The Mystery Packet from nowhere (Score:1)
I was once installing IP-forwarding on my secondary box to cleverly avoid paying extra for cable. So me and my friends were fixing and configuring. Then my firewall prompts that someone unauthorized is trying to send a packet to me. First I just thought "what?, this usually happens when I'm surfing". Then I realized we've put the cable-line on the other machine and my box was on an empty hub.
I have stong reason to believe it had somethong to do with me having LOTS of electronics (15-18 appliances) plugged in my room.
Back when i had a TV, the picture would sometimes shake when the fridge whent on (mind you, the fridge is in the kitchen, a totally different room).
Re:The Mystery Packet from nowhere (Score:2)
Studio displays. (Score:3, Interesting)
Ever get the feeling you're being _bathed_ in RF?
--saint
Re:Studio displays. (Score:1)
There's an issue where the wiring gets shorted out on the PowerSwitch of the LCD Monitor.
An AASP can re-wire the monitor, or Apple can setup a Mail-In Dispatch Repair.
1-800-sos-apple (800 767 2275)
Its just being friendly! (Score:1, Funny)
(afterall, they look like desklamps anyway)
(from visual_bob@hotmail)
Commodore 64 (Score:1)
GSM Phone and doorbell... (Score:1)
Whats really interesting is that my door bell goes off just before my phone rings (1/2 second or so). I have a little Radio Crap wireless one, and it ALWAYS (100%) goes off just before my phone rings, if my phone is close to it. Kinda creepy the first few times it happened.
Theres a LOT of sources of electronic noise out there, it's pretty funny when stuff like this happens.
PEBKAC (Score:5, Funny)
Okay, look in your office, and put your hand on the lamp. Is your hand resting on the thing with a rounded base, a stalk, and a flourescent emitter at the end? That's your computer. Don't worry, a lot of people make that mistake.
Re:PEBKAC (Score:1)
Re:PEBKAC (Score:1)
Geez
i wouldnt. (Score:1)
walk in hit a switch computer and light go on.
i usualy work with a lamp on anyways. one less button to push later.
Some funky (Score:3, Informative)
on similar lines... (Score:1)
Its the IR port on your computer. (Score:2)
Florescents are noisy (Score:2)
More strangeness (Score:1)
My home PC came with no less than two sets of crappy speakers. (As a music lover, this insult was severe enough to make me decide to buy the next PC in parts =)
Anyway, one set of the speakers was supposed to be attached to the monitor somehow (more cabling than anyone ever needs).
I plugged the speakers in. I couldn't hear a thing.
I unplugged it. It worked.
I used the speakers from my old PC, and now I have a nice 4.1 speaker set - so that... I... don't... need to... think... of the... haunted... speakers... in the... *shiver* box... in the... cellar. *shiver*
Maybe I won't sleep that well tonight, now that I was reminded of this thing...
Re:More strangeness (Score:2)
Re:More strangeness (Score:1)
A very much unbranded monitor from a mysterious country in the east.
People suggested electromagnetic induction or something equally UFOish...
Re:More strangeness (Score:1)
Is it a UPS? (Score:1)
Most vendors are confusing the term UPS. It once meant a power supply with your computer _always_ receiving power from the batteries, while the batteries were being recharged from the mains.
Nowadays a lot of vendors use the term UPS to mean that power is taken directly from the power lines to both the computer and the batteries when availiable. When the power goes out a relay drops out and switches the computer from the mains to the batteries.
Basically the first type always provides perfect power (assuming the inverters generate a sine wave -- many do not), whereas the second type provides nothing more than power filtering unless there's no mains.
While filtering is usually better in a UPS than in a $5 power strip, it doesn't filter everything. To prove this, hook up an intercom that uses the AC to transceive to your UPS and see if you can communicate with another at the wall plug.
Unless your UPS uses some form of solid state relay (not likely) you can test if its the "real thing" or not by pulling the power and listening for a click inside the UPS. If it clicks, you have a standby power supply.
Not that the noise from the one lamp should _really_ affect the other, but hey, I don't own one.
new imac (Score:1)
Re: Fluorescent Lights Magically Activates iMac? (Score:1)
Fluorescent lights cause RF interference. (Score:2)
Fluorescent lights cause RF [interference], I would suspect that is raising a rail in you network cable.
We use large numbers of ADSL modems pushed towards there upper bandwidth limits to serve a digital TV project. As you can expect some of our hardware enginners have become real experts in the field of RFI and crosstalk. We had a particular set of problems that could not be tracked down, crosstalk was supected and test gear indicated RF interference on the lines.
However further tests revealled crosstalk was not the cause, the RFI spikes occured in exchanges that had not even been xDSL upgraded and somebody noticed when the engineers entered the exchanges, the situation deteriorated and QoS problems got worse. The network management systems reported thoughput and packets dropped. This was before the networking had been touched the, after much head scratching the problem was discovered as the Fluorescent lights, they had to ve removed from every one of our exchanges because of the RFI problems they cause.
UPS and Power Strips don't tend to stop bad things (Score:2)
Similarly, power strips generally do nothing to protect you from anything except too much current. Voltage can drop way below or rise way above normal and the power strip would keep supplying this power. If your power strip doubles as a surge suppressor, you might get some protection from voltage spikes in addition to too much current, but don't confuse this with a real line conditioner, which would remove noise from the power as well and guarantee you a clean power source.
Could be RF interference... (Score:1)
Power Spikes (Score:1)