I have a  here. Whenever it goes to stand-by, sleep or is shut down I hear a VLF sound (presumably close to the ~20 kHz maximum of the human ear) that's even better to hear if the battery led blinks because the sound is intermittent then. When I disconnect power and such the LEDs go off, the sound goes off, as well. When it is operating the sound is probably there, as well, but I can't hear it since the fans are terribly noisy.  I tried to use this  on my tablet to give you more information but I can't even calibrate it since:     Failure: Unstable sound source, ΔL = [5.5–10.5 at different tries]dB   What's causing this sound and is there a possibility to get rid of it?  (I'm absolutely able to master advanced tools like screwdrivers, soldering guns, etc.  I had it open dozens of times for fan cleaning and thermal compound renewing.)  UPDATE  I read the suggested . The instructions how to possibly get rid of it, however, are a bit too vague for me (I'm a high-power electrical not an electronics engineer):     add a load at the output (a resistor)   Of which size?     put some insulating viscoelastic caulk on the noisy components   What about heat if I put that around a DC/DC converter? 20&nbsp;V (external power supply) converted to a voltage suitable for LEDs can produce quite an amount of heat, IIRC (crafted 12&nbsp;V car to 5&nbsp;V CMOS once), can't it?
120667
I have a power supply that buzzes when nothing is connected and is silent when there is a power drain. What could it be?  It's a PC power supply that I used to power an LCD through its 12 V line.
77462
This is the most interesting thing I have seen! I have built a  that sends data (D0-D7) to a DAC (ADV2175). The design worked fine and I just have a low frequency alias noise (). This noise was present on all my ground planes (This is in prototyping stage and that's not unexpected from the test PCB).  I started tracing the noise path by disconnecting wires to see when the noise is gone. Surprisingly even after disconnecting all VCC and GND connections (+ all VREF and logics gone to 0 or 1) the noise was present yet. The more unexpected behavior is when the DAC is just connected to DATA port+ CLK pin (all coming from the source FPGA, NO VCC or GND), it continues working and a sine wave is produced (but with the same noise)!!!  First I thought it may receive its VCC/GND form the logic 1/0 fed into it but if it was correct, it should not have produce 0x00 and 0xFF levels, but it makes those levels correctly (I changed 0xFF data stage to another level and a notch appeared on top of the waves. this shows it can build oxFF correctly).    This is a big challenge for my PCB design, as if this device really takes its GND from the data port, instead of the dedicated pins, I will have a hard time for designing a reliable ground plane for it (the return voltage should go back to a logic noisy environment and analog-digital ground plane isolation may be impossible).  Can anyone explain what is happening there?
67261
Everybody has had the time where water gets all over their electronics, and the whole thing gets ruined, like cell phones.  At that low of a voltage (3-5&nbsp;volts), I don't understand why it is such a short-term harm (long term makes sense - corrosion, etc.)  If an LED was in parallel with water, maybe a bit more current would be drawn, but it doesn't seem to be enough at all to short out the system, and the LED would still shine.  So what is it that permanently damages some electronics and what is the cause?
102422
Based on numerous internet resources, speaker wire acts like an antenna which picks up the transmitted signal of nearby cellphones and causes the speakers to buzz. But I'm not really buying that...  A 3.5 mm speaker cable is designed to carry 1 V. I've seen old setups where PC speakers are powered directly from the 3.5 mm jack (and I've tested playing unamplified sound directly from a PC through the jack, although the volume in my setup was not very high at all). How can the tiny bit of EM emitted by a cellphone radio cause a speaker system, designed to operate off of a fluctuating 1 v signal, produce such a loud buzzing noise? I couldn't imagine the EM generating more than a few micro-volts in a receiving antenna. Am I wrong?  Thanks.  Updated - corrected voltage of line out to 1 V (see comments)  Update I looked it up, and yes it seems GSM transmits at 2 W. I'd like to do a sanity check with that figure to verify some of the answers which state that the transmitted power is significant. My physics is quite rusty, but I'll try...  We know that the intensity of EM radiation around a source is:  $$I = \frac{P}{4\pi r^2}$$  So let's say we have a wire 2 m long and 0.2 mm wide (I hope this is a valid approximation for the wire) that is approximately 2 m away from a transmitting GSM module.  Then for \$P = 2 W, I = 39 \frac{mW}{m^{2}}\$  Multiply that by the surface area of the wire (0.2 mm * 2 m)  The total EM power along the wire is then 16 \$\mu W\$.  Like I said I'm quite rusty, but is this not correct? Is this really significant enough to produce that sound without being amplified somehow? Perhaps the signal resonates? Or interferes directly with sound cards?
51243
I never had to deal with sound and I am pretty sure some of you guys have some experience in that kind of application.  My question is more about getting some tips on the different ways to implement an embedded system based on an AVR that plays sounds. More precisely:   What library should I use? Which sound format should I choose? Do I necessarily need a dedicated memory chip aside the MCU? If yes, which one would you recommend? Do you have some code sample to share?   As always, I know that everything depends on the target application. Here are a few precisions:   I want to make a toy for the kids of a friend of mine, the idea is to have a short sound lasting no more than 30[s] I am not interested in high fidelity sound Power consumption matters
16853
I'm currently encountering a problem when using a relay switch with a 5v receiver. When using the same receiver with a row of LEDS it works flawlessly. I've noticed that the relay keeps making the switching noise over and over like I'm pressing the transmitter really fast apart from the fact I'm not. Also, when the transmitter is moved closer to the receiver from 20" to around 1" the problem stops. Below is some circuits to help show you my setup.  Any help appreciated thanks.  Setup Specs   USB 5v DC (2AMPS) Receiver (XY-DJM-5V - SC2272-M4) Relay (SRD-05VDC-SL-C 5V DC) Transmitter (XY-04) Diode (1N4001) Transistor (2N2222A) Resistor (1.8K Ohms)          &ndash; Schematic created using   Antenna Signal Workaround or Booster  I believe this issue is related to wireless signal on D0. Basically above 20" inches the output to the relay drops from 5.05v to 0.5v and is obviously causing the problem. I think I need to boost the signal or replace the transistor with something that triggers at low and high current but have no clue. Any help appreciated, I'm new at this.  Board Setup
114451
I need a sound to play when I shutdown. In Kubuntu, there's shutdown sound. But Ubuntu, not anymore
105863
There's a &quot;default beep&quot; (as defined in System Sounds) that emanates from my computer every so often. It kind of goes like this (where each number is a &quot;default beep&quot; sound): 1, 2, 3, 4,  5. So there's a distinct pattern to it. I thought I had this figured out a way to figure out what was happening by going to Control Panel-&gt;Ease of Access-&gt;Ease of Access Center-&gt;Replace sounds with visual cues But that just isn't the case.  Whichever window I click on, that one displays the visual queue when this happens. It's driving me crazy, and I can't figure out which program is causing this. Update: it appears to only happen on one user profile on the computer...does that help? Update 2: Discovered that this sound was coming from a utility on my laptop called ASUS NB Probe; I'm certain that it is emanating from this program because the error message displayed by it changes in sync with the sound playing. Apparently the  feature of my hard drive was reporting an issue. It displays the issue for a brief second and then makes it disappear, I'll have to keep watching it to see what it says, but I believe is says something about a read. I have an external hdd connected with eSATA to a container of sorts (BlacX) that you can plug two hdds into. I have one hdd attached and it's a Western Digital WD1001FALS - 00E8B0 Thanks again!  Now I'm off to go around the Internet and report on this...since I posted it so many places!
119285
I bought a Dell Inspiron 7000 notebook and after a couple days of use the sound just stopped working. Now it is showing an "Dummy Output".  I already tried all the answers in StackOverflow, like force reload alsa, kill pulse audio, make a lot of changes in the /etc/modprob/alsa-base.conf, update kernel, update DKMS...  Dell official support said they can't help because it is an unsupported OS, but I'm using the system that came with the equipment from the factory.  I hope someone could help me.
66315
OS: Windows 8.1  I'm noticing that when playing something from VLC (though it happens when playing audio from Chrome) that my sound will pseudo-randomly become quiet.   Chiefly it happens on the 'new tab' screen of google chrome, as well as google searches through windows chrome. It will occasionally happen when I open other applications - though I've not yet found any rhyme or reason to it.  Device is the built-in realtek device through my headphone jack, driver is most current according to their website.   Not really sure how to diagnose or fix this. Help appreciated.  EDIT: Logging in as a different user fixes the issue. Disabling all extra chrome extensions does not. Still looking for a solution for my regular user account.  Related:   List of things causing the issue:   Chrome Launching a windows 7 virtualbox VM (not VBox manager though) Mumble Will update with more as found NOT Foobar2000 (I had suspected the issue may be coming from applications that play sound?) Installed Skype to test, during the initial 'setup' of my account (for sound/mic/video) my audio was hushed, despite that I have the 'communications activity' set to 'do nothing'.
35125
So, this question has been bugging me a lot, I used to have a few lovely little toys (well, not so much toys as a pentium pro and a really old Intel 80386DX microprocessor) What I noticed is that when the CPU's are under load they generate a most delicious noise which reminded me of when I used those computers for actual things (the 80386 had DOS 6.2 at one time and I ran a small unix server on it a few years later, the pentium ran windows 95 and then later windows 98+ and even later I somehow barely got xp running on it), I almost dare say it's nostalgia.  Anyway, that noise made me curious, what causes it? My first hypothesis for this rumbling/humming sound is the fan, so I tried removing every last fan, the noise didn't stop, it was actually easier to hear when the whirring of the fans wasn't there, I then spent hours testing each piece of hardware and came to the conclusion that the CPU itself was making the noise and then decided that I was happy with my conclusion for then, I recently remembered it and I got curious as to what generates it.  I don't own those machines anymore (alas I had to get rid of them due to moving) but I have observed that newer CPU's make the same noise, just a lot fainter and more subtle, so I do think it has something to do with the underlying architecture.  Anyway, before my rambling carries off too far... What causes the noise and is there any correct terminology for it? These questions are derived from a few hours on google and getting nothing but people asking silly questions such as "Why is my hdd ticking?" or "Why is my CPU producing a high pitch noise?" (the latter is closer but not what I am looking for as the noise is low pitch and quite distinct, if you've heard it you should know what I'm talking about)  I want to know this for a couple of reasons, curiosity is one but I also want to utilize this sound effect in a project of mine.  Now, some of you may point out that CPU's have no movable parts and are thus incapable of generating noise, then what could possible causes be? I tried removing everything redundant from those machines and the sound prevailed, the only things I didn't remove or replace was the mobo's and the cpu's themselves (because finding such old hardware proved harder than expected. oh and this part is what really sparked my curiosity as to what was generating the sound as the fans were silent when just powered on, and the machine kept making noise without them (I ran them at short 1 minute intervals))
17893
I know this is a common problem and have read other topics but couldn't resolve. Anyways yesterday I found a solution - I have 2 graphic cards (hybrid) and they were both on. So I turned one off and installed Jupiter for power management and from there on the fans were quiet and I was happy as hell.  However (:)), yesterday evening I also updated the system and the fan and it's noise came back. I checked whether I am using only 1 graphics card and I am.  c0dehunter@mintBox ~ $ sudo lshw -c video [sudo] password for c0dehunter:    *-display                       description: VGA compatible controller        product: RS780M/RS780MN [Mobility Radeon HD 3200 Graphics]        vendor: Hynix Semiconductor (Hyundai Electronics)        physical id: 5        bus info: pci@0000:01:05.0        version: 00        width: 32 bits        clock: 33MHz        capabilities: pm msi vga_controller bus_master cap_list rom        configuration: driver=radeon latency=0        resources: irq:18 memory:c0000000-cfffffff ioport:c000(size=256) memory:fbcf0000-fbcfffff memory:fbb00000-fbbfffff   Maybe the problem is (false) temp reading from GPU?  c0dehunter@mintBox ~ $ sensors acpitz-virtual-0 Adapter: Virtual device temp1:        +44.0°C  (crit = +105.0°C)  k10temp-pci-00c3 Adapter: PCI adapter temp1:        +47.0°C  (high = +70.0°C)                        (crit = +115.0°C, hyst = +110.0°C)  radeon-pci-0200 Adapter: PCI adapter temp1:       +127.5°C     The thing that is weird is that if I boot into Windows the fan is still at full power (previously it wasn't). Did I f--- up my hardware with software? :)  //OH, yes - I forgot to mention that my laptop is not hot at all. The temps are about 50°C.
54108
Whenever I shut down my computer, or put it in sleep/hybernate, it turns on after two seconds. It doesn't post, it just powers on and then idles. To actually turn it off, I switch off the psu. The problem is now, whenever I switch the psu on and try to boot, it doesn't always turn on. It takes a good amount of flicking the psu switch on and off before the motherboard lights up.  So far I've determined the things its not:    its not caused by the mouse or network waking up the computer. I've been able to go into hybernate for the past year. And all "wake on X" settings in the bios are diabled.  its not a scheduled task waking up the computer at a given hour, it occurs every single time  its not due to an upgrade or new installation, since I haven't done either in a very long time   I'm sure its a hardware issue. So I'd like to know, is my psu dead, or the motherboard? The psu is an Antec Earthwatts 600w, the motherboard is an Asus P5Q-E, both one year old.
75428
What I would like to do is have an LED turn off 1 minute after the power is turned off. The LED would be on all the time when power is on. Thus:  Turn power on: LED comes on immediately. Turn power off: LED stays on for 1 minute and then turns off.  This is to signal when someones eyes have adequately adjusted to the dark in a darkroom.  Thanks in advance.
32214
I have a a MacBook Air that works fine except popping up a shutdown dialog if left untouched for a couple of seconds (seems to be a consistent duration around 3 seconds or so). Hitting Cancel or Esc prevents the shutdown.  If I keep fidgeting around with the keyboard or trackpad, there's no shutdown attempt. I can even place something on the Fn key to keep the OS from shutting down.  It seems like some inactivity timeout etc. gone awry.  When taken to the Genius Bar for initial assessment, the guy there said it was probably the power button needing a replacement. But, I don't think this is the case, as the power button is functioning normally: I can still press it to explicitly initiate a sleep/shutdown.  There's a chance this was triggered by water damage. There was a recent water spill incident to which I acted quickly by turning off the machine + turning it upside down + not using it for a long while + keeping it in a box with rice to absorb any leftover humidity. But even if this is a water damage, I can't imagine a damage that manifests itself with this very narrow malfunction of wanting to shutdown on a short period of in activity. Absolutely nothing else seems to be wrong with the machine.  Any pointers? Any things I can try to (a) diagnose the root cause fix or workaround the problem?
37633
Basically, I'm looking for some do's and don'ts. Is it bad to keep my laptop plugged in when I'm not using it (majority of the time)? Is it bad to plug it in once I've finished using it (with it having something like 30% or 70% life left)?     This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.
119277
I am building a steady current source which delivers steady current (0-20mA) to an LED. The brightness of the LED (current) is controlled through a potentiometer's voltage and a voltage follower as shown in the picture below. Further, I want to blink (modulate) this LED with a square pulse frequency of 2kHz using a switch between the transistor gate and the voltage follower output.  The problem is that every time the switch closes, spikes are produced at the base and as a result at the source. Even when I reduce the current of the LED to 1mA (example picture 2), the spikes don't go away. Only when I set the current of LED to 0 do the spikes dissapear.   So the question is how can I remove/reduce these spikes? Is there some way?  [