while I was sitting in city center with so many LED (especially red ones mounted) signboards and I was bitting an apple, the signboards suddenly begin to shake for only a second while my head is shaking.   I couldn't understand why this had happened to my eyes? Maybe the XTALs in the LED-driver-circuits are out of the frequency because of high voltage or so many times these are used, and/or grid's frequency has been added on to the device.  What should be done to prevent this frequency shake?  Is this topic belongs to harmonic distortion - THD ? That maybe a reason by XTAL's frequency?
121150
This question might sound silly, but it is very serious (although geeky, I must admit). When I use my electric toothbrush in front of my alarm clock (one of those with a big red LED display), the numbers seem to break apart. Why?  With my current alarm clock the first 3 segments (a,b,c) make one group and the other 4 make another one. The striking thing is that both groups seem to slowly oscillate, in anti-phase. I cannot affirm that the grouping is the same for every display of the kind -- and I cannot check now because I only have this one LED display at home -- but I've seen this illusion on many different displays in the past.   I think this illusion is fascinating (told you I'm a geek) and I would like to understand why it is...  I believe that it has something to do with    1) the vibrations of the toothbrush making my eyes oscillate in their orbits so the image seems to move (a bit like when you touch your eye on the side with your finger and the whole image seems to move),    2) with the periodic refresh of the segments. I suspect that the two groups I'm seeing actually correspond to two groups of bars blinking in sync, so there really are two groups, (but why do they dislocate like that?)    3) with our periodic perceptual "refresh rate". Something similar to what makes us see car wheels as stationary when they rotate at a certain speed.   I must say my competence in electronics is close to zero, so my questions might be trivial to you guys. How does the refresh of the line segments in a 7 segments display happen? Is it cycling (a,b,c,d,e,f,g,a,b,c...)? How come I see two groups, then? At what frequency are the LEDs blinking? I understand some of these questions depend on the specifications of my alarm clock, but since I've seen this illusion on basically every type of LED display I passed by with my toothbrush (microwave, VHS video recorder (yes the story started long ago. I bought the toothbrush I'm now using just for understanding this silly illusion, but it was actually as a teenager that I noticed it)...), I guess there is something constant there...
76191
I'm suffering from the dreaded . The problem is intermittent and can be "solved" by putting the computer to sleep or restarting it. I hope simply restarting the graphics drivers will remove the symptoms of the problem.  would seem to indicate that restarting the graphics drivers is possible in Windows 7. My question is: how?
49481
Well, it will be a broad schematic. To summarize, there my approach is:   Yellow part is for oscilations at three different freqs(around 0.8 - 2 kHz, different for each of the three signals), sinusoidal, I can get nice 6 Vpeak sine waves, observed with oscilloscope, no noise, smooth. In the orange part, I use classical potentiometers to change the amplitudes of the signals. For this part, I suspect from the potentiometers, I know they are very unstable but I somehow have to use them. Then, red part, adds the signals together, nothing fancy. Finaly, the green part is my design to drive an 8 ohms speaker.   Now, when I connect the speaker, I get a noticable noise on the speaker output. It is both understandable from sound and also checked by oscilloscope. I have heatsinks for transistors, and I suspected from them for the reason I explained in my .     when I inspect the signals in the circuit via oscilloscope, I see there is some noise on waveforms, while trying to understand where it comes from, I have touched the heatsink (...) It becomes much smooter.   However, then, I thought it might be resulting from something else and wanted to get your opinions about it. What can I do to minimize the noise ? Would soldering things on something like  solve things?  Things to note:   I got satisfying results in simulations, everything was as I wanted. However the reality spoiled me. I implement the circuit on a breadboard for now, while prototyping, I suspect it may be bad in terms of noise. I don't know it is relevant or not but the noisy parts are mostly in the upper parts of sinusoidal waves.   Thanks in advance.
78494
I tried to reproduce the results from the  unfortunately the video link is broken. And I might have overlooked some related settings.  The spot light is barley visible on the ground.    Increasing the Density of the Volume Scatter Node darkens the sky texture but leads to some light cone from the car's headlight. (only 10 samples in preview).    Which settings do I need to change or should I try a different approach?  Integrator settings are default and spotlight settings were copied from the example found in the docs.  Related:    (pre 2.7)  (BI only)
44424
I own, an about a year old, rig which carries quite the punch. And for a year, I was happy. Not that long ago things began to crumble.  I first detected the problems running my dual monitor setup. For some reason, tearing and artifacts are appearing when I run with two monitors plugged in my nVidia GTX 460. I thought it was a graphics hardware problem and switch to an older RADEON 5850, but the problem did not go away.  I began experiencing BSODs on very specific things related to USB devices. If I shutdown the computer with my external banking security device plugged, it will BSOD, if I connect my external Rig Kontrol 3 audio interface it will BSOD as soon as I try to run any ASIO applications that use the audio interface. I also noticed magic ISO randomly blue screening the computer.  I've learned to avoid these BSODs because they are very predictable and the computer feels stable enough, but it also feels a lot slower than it used to be. The problem is that I have no way of actually measuring this, it's only a feeling I have, that something is a miss. If only there was to a way to compare my benchmarks against other systems with similar hardware.  This seems to be mostly noticeable during software installation processes and during draw calls in Windows.  I'm not ruling out that there's a problem with my GTX 460 card, but I think my motherboard is bad and thinking about replacing it. I've ran all diagnostic tools I know of (memtest, scan disk) to rule out memory issues and corrupt drivers. I've tried reinstalling everything, but to no avail. If anyone have any experience dealing with this kind of situation I love to hear about it. Because I hate to throw away money on something which wont fix the problem.  Edit  The motherboard in question is a Gigabyte P55 UD4 R1.1. BIOS F9 from 06/25/2010. Though that reminded me about another problem I have. If I run the @BIOS update utility the computer will BSOD. This used to work fine, but at the same time everything else started to break down, I got instant BSOD if I tried to launch that program.  Edit 2  I'm gonna keep adding to this question for every time I experience another damned and forsaken hardware glitch until I get a satisfactory answer/solution to this.  Today, the computer ran through POST then black, just black. Everything appared to be fine, except no video signal... reboot. same thing, but this time the POST screen never appeared. After a minute or so the video signal came back. I checked the cables, didn't find anything that indicated a loose connection.  I'm placing a order for a new mainboard today.
119252
This past week at Menards I bought 2 Smart Electrician® 3650 Lumens 46" LED Linkable Shop Light Model Number: 0053-0011  |  Menards® SKU: 3481400.  The LED shop light fixture has a glow to it. Looked like the LEDs were turned on, but not all the way. The power switch is turned off. Don’t know why I did this but I took one of those three prong adaptors converters to two prong and to my surprise the light fixture didn’t light up. I unplug the cord with the adaptor and turned it around and it still didn’t light up. The power supply electronics inside the light fixture must be using the earth ground wire somehow. Using my volt meter. I measured to earth ground to the green wire that comes out of the adaptor and to my surprise depending how I plug in the adaptor. I’m getting 112 volts AC. That's because the adaptor isn't keyed and I'm switching the HOT and NEUTRAL around depending how I  plug it in.  I connected the LED light fixture to “Safety Analyzer tester”. When I press the “Open Ground” button, the fixture stops glowing (lightly lite LED’s).  Looks like the power supply circuit inside the fixture has a connection to “Earth Ground”.  I then switched the “Normal” on the polarity switch to “Reverse” and the LED’s were off. Switching the Neutral to open position has no effect. I'm thinking of taking them apart and see inside what's going on or take them back.  I figured out the problem.    In this light fixture you can clearly see the white wire (neutral/common) is connected to the light switch, turning the power off the LED light strip. Commonly we switch off the “HOT” to your light socket so when you change your bulb you have a less of a chance of getting electrocuted (that’s another story for later). Sometimes in Power supply circuits they place capacitors in there to help filter electrical noise out. Also known as suppressers (electronics to reduce unwanted noise or oscillation in a circuit or unwanted frequencies in a signal). Depending on how or where they are placed in the circuit it could possible cause some issue if not installed correctly or if the circuit isn’t designed correctly.   Since the BLACK live wire is connected to the LED PCB all the time, anything connected to that line will potentially be LIVE voltage, that way when I disconnected the earth ground from the socket and measured 112 volts on it. My guess is they have capacitors connected to both LIVE and NEUTRAL to the earth ground wire.  The current is flowing through capacitor C2, just enough to turn the LED’s on slightly. If the switch was on the hot side, this problem wouldn’t be happening. I still may use them just not connect the “earth ground” wire. Because that’s providing the return path for lighting the LED’s.
112974
It's been happening to me for years. I finally decided to ask users who are better with "practical physics" when I was told that my experience – that I am going to describe momentarily – prove that I am a diviner, a psychic, a "sensibil" as we call it. The right explanation clearly needs some electrodynamics although it's "everyday electrodynamics" and theoretical physicists are not trained to quickly answer such questions although each of us has probably solved many exercises that depend on the same principles.    When I am biking under the power lines – which probably have a high voltage in them – I feel a clear tingling shocks near my buttocks and related parts of the body for a second or so when I am under a critical point of the power lines. It is a strong feeling, not a marginal one: it feels like a dozen of ants that are stinging me at the same moment. It seems almost clear that some currents are running through my skins at 50 Hz. I would like to know the estimate (and calculation or justification) of the voltage, currents etc. that are going through my skin and some comparison with the shock one gets when he touches the power outlet.  Now,    my bike that makes this effect particularly strong is a ; the speed is about 20 km/h and the velocity is perpendicular to the direction of the current in the power line; the seat has a hole in it and there is some metal – probably a conducting one – just a few centimeters away from the center of my buttocks. It's plausible that I am in touch with the metal – or near touch; my skin is kind of sweating during these events and the liquid isn't pure water so it's probably much more conductive than pure water; the temperature was 22 °C today, the humidity around 35%, clear skies, 10 km/h wind;  may be between 22 kV and 1 MV and at 50 Hz, the altitude is tens of meters but I don't really know exactly.   What kind of approximation for the electromagnetic waves are relevant? What is the strength? How high currents one needs?   Does one need some amplification from interference etc. (special places) to make the effect detectable? (I only remember experiencing this effect at two places around Pilsen; the most frequent place where I feel it is near Druztová, Greater Pilsen, Czechia.)   Is the motion of the wheels or even its frequency important? Is there some resonance?  Does the hole in the seat and the metal play any role? Just if you think that I am crazy, other people are experience the effect (although with different body parts), see e.g.  and .  seems to suggest that the metals and electromagnetic induction is essential for the effect but the presentation looks neither particularly comprehensive nor impartial enough.  An extra blog discussion on this topic is here:
35503
I recently bought  white LED reading lamp. I like it a lot, but the "white" light produced is significantly blue; I'll guess its  is about 5000K.  I've noticed that, when this is the only source of light, printed text appears slightly fuzzy, and is more difficult to read than with a standard incandescent reading lamp. My guess is that this is  causing color fringing in my eyes, making it harder to read with this new lamp.  Is there a way to make this lamp less blue using some sort of transparent/translucent filter over the lens? This could filter out some of the blue end of the spectrum, or include a  to convert some of the blue to yellow (as  do). The fluorescence idea would be better, as there'd be less light lost. I don't want to go too far, though; a strongly yellow lamp might be worse for reading than this currently blueish lamp.
113924
I recently got a desktop LED lamp, and I feel a "strange" slight vibration when touching the metal case. I found that other devices also have high voltage on their case.  What is the reason/trade-off to design the PSU that way? Are "real" transformers inefficient? Even if it's harmless, why is the high voltage connected to the metal case, and not just through insulated wires?    When I turn the lamp on, the setup in the picture measures the power line (220V) 214Vpp (59Vrms). When I also touch the metal case, the voltage drops down to around 30V.  AC adaptor:
2777
about the use of battery/freewheel based Frequency Regulators confused me about how the 60hz frequency of the North American power grid was set--saying that it was kept at that frequency by balancing load and supply. I used to think that it was only voltage which was affected by this balance, and that the frequency was determined by the speed of the rotors in the generator. EG see .   Can someone help me understand the physics behind this?
76354
I'm struggling to understand the purpose of the resistor circled in red, I know it has something to do with DC biasing and the feedback on the circuit (as the capacitor will cause AC bypass). But I'm struggling to understand the exact circumstance where this would be needed. Is it a change in supply voltage, or change in transistor beta? And the exact mechanism that would cause the resistor to solve the problem.
12483
The aluminum Macbook Pro gives a mild shock when connected to a wall socket and charging. It only happens when I'm, for example, not wearing shoes or slippers and my feet are resting on the ground (i.e. by body is acting as a conductor). I contacted apple and I was told to perform the following steps:  Shutdown  hold ⇧+ctrl+⌥+power for 10 seconds  wait 30 seconds then hold ⇧+ctrl+⌥+R+power (Let the Mac reboot three times with that apple tone, then let go. The Mac reboots again.)   This did not fix the problem and I was not told what these steps were supposed to do. They have asked me to purchase a three pin version of the adapter and see if that fixes my problem. My last MacBook Pro was giving pretty severe jolts towards end of life. Hence a bit concerned. Question  Has anyone here experienced such a problem?  Is anyone aware of what the above sequence of steps supposed to do?  Also, will this damage the Macbook in some way?
113794
If you have multiple waves of different frequencies, the interference from the different waves cause "beats".  (Animation from )    Let's say that a green dot in the above animation reaches your ear a few hundred times per second.   Is it possible to hear this phenomenon (wave groups occurring at frequencies in the audible range) as its own tone?
53454
Under normal circumstances, the Dell E2310Hc LCD Monitor seems to work fine.  However, when I display an large array of hash characters ("#") a faint buzz can be heard from the monitor.  It appears to be correlated to the periodic pattern somehow:   Increasing the size of the pattern (i.e. changing the font size) changes the frequency of the noise. Adding more pattern enhances the sound. Increasing the contrast increases the intensity of the sound. Color does not seem to affect the sound. Increasing the contrast of the pattern w.r.t. the background increases the sound. Edit: Horizontally tiled patterns make little contribution, but vertically tiled patterns cause the majority of the noise.   What could be causing this?  I also noticed the same issue with another LCD monitor but it's a lot less perceptible.
64689
I have a few 3mm color-changing LEDs which I harvested from a toy. They fade in between all different colors, and then after a little while, they blink crazily between all the colors. After a few moments, the cycle repeats.  What is interesting about them (and what I wasn't expecting) is that they only have two leads, like a normal hobbyist LED.   I understand that, like an RGB LED, they have multiple elements (probably not the right word) inside. But how do they achieve the color changing and cycling?  Here is a picture of the LED in question:    Notice the little bit of black material inside the LED. Could this possibly be a tiny chip?
77534
I am trying to develop a very high reliability product, with a MTBF exceeding 100,000 hours, hopefully in the 250,000 hours range. Yep, I know - stupidly high reliability, at least 10 years.   Most LED's I've seen have a reliability rating of only 20,000 hours. What happens after this? Do they reduce in output too much? Are they usable as power indicators past this point?
26970
Context Feel free to skip this section. I ramble a bit. This is a desktop computer. My motherboard is a MSI P67A-C45. The two memory modules are 4GB DDR3-1333 in DIMM 1 and DIMM 3, dual channel. A few months ago, I started experiencing random graphics glitches resulting in my video drivers (nVidia) crashing and restarting occasionally. This was especially bad when hardware acceleration was used, especially in 3D FPS games, even with the 10+ year old goldsrc engine. It would also happen when playing flash videos, and occasionally when doing nothing. Most of the time, it was fine. It was only after the system had been up for a while - uptime, time since last reboot, not hibernation. Once the glitches started, I had to turn the computer off and leave it off for a few minutes. I suspected the video card - perhaps overheating? But temperature monitoring programs reported GPU temp at a nice cool 40 degrees Celsius. More recently (last week or two), when leaving the computer on overnight, I wake up to find it had BSoD'd, with a memory related error. I'm currently rerunning Memtest86+, so I can't dig up the exact error message/codes, if anyone really wants them. At the same time, some programs started crashing randomly (&quot;xxxx has stopped working.&quot; with a close button). This would happen to Firefox and the aforementioned FPS game. I don't really run anything else, and the crashes are random. That is, they could crash immediately or run fine for the whole time I use them (several hours). The troubleshooter's nightmare. Memtest86+ On the first run, somewhere over 12 hours, I got the following results:  There's a few irregularities. Firstly, I have 2x 4GB DDR3-1333 modules in DIMM1 and DIMM3, dual channel. This is reporting DDR3-8247, whatever that is. Secondly, all the failing addresses are outside my total RAM capacity. That's not all that much help when trying to figure out which module may be failing. Evidently, at least one is failing. I reseated the modules and tried again:  As you can see, the frequencies and latencies are completely different. The latency values are much closer to what I vaguely recall seeing in CPU-Z (or was that HWiNFO32?). This test has only just started, so it's entirely possible those values changed sometime during the test. Also, considering errors only started cropping up in the later passes, is it possible that this is an overheating issue? Consider I've been using this computer for about a year now, and only in the last three or so months have things happened. My main question remains: Why is the failing addresses higher than my capacity?