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- Опубликовано: 27 авг 2024
- Dave investigates the piezoelectric effect in multi layer chip capacitors (MLCC's). In this case, on the backlight inverter on his own BM235 multimeter.
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I love that you are honest enough to critique a product with your own brand on it. You are awesome.
Isn’t that great? an EEVBlog product he didn’t even design.. and doesn’t have a schematic for it. lol
Ah, there is an easy fix in the works for this. All you need to do, for around twenty years, listen to loud rock/metal music. No more annoying high-pitched frequencies, ever!
Thanks Motorhead, you really saved my bacon!
+Darthane But then you get tinnitus and chronic ear ringing :(
+Darthane Also helps when living with a women?
Brian Eastwood Can't hurt, and besides, you can just put some music on!
Nice video. Thumb up, as usual.
Here's a story about the piezoelectric effect that some might find interesting. Several years ago I designed a Bit-Error Rate Tester (BERT) that ran at 43 Gb/sec. It included 17 serial channels that each ran at 2.5 Gb/sec, and each channel needed its own separate PLL to produce the 2.5GHz clock, because I had to be able to adjust the relative phase angles. (You can control the phase angle of a PLL by feeding dc current into the loop filter, which I did with a DAC.) The eye patterns would look okay for a few seconds, and then suddenly get really cloudy, indicating jitter. Then I noticed that tapping the side of the chassis with a screw driver made a burst of jitter. I thought is was a loose connection, but it turned out to be piezoelectric. Each PLL circuit had a VCO that got its supply voltage from a low-noise LDO from Micrel, and I used high quality ceramic caps on the output of each LDO. Turns out, just a 5uV shift in the supply due to piezo effect was enough to push the VCO frequency slightly, and it took a few microseconds for the feedback loop to compensate. But a few microseconds is a whole lot of bit periods at 2.5 Gb/sec, and the very slight freq shift caused the phase errors to accumulate (phase is the integral of frequency). The result was that the phase difference between the channels would bounce as must as 35 degrees. Replacing the ceramic caps with low-ESR tantalums eliminated the problem.
I've heard this kind of noise in lots of other products- but you really have to be looking for it. great to see Dave doing this kind of investigation and fix on his branded gear! practice what you preach & openness & transparency and all that! you rock Dave.
As a test engineer I found out this problem some years ago while I was working on a SLIC device (a telephone line driver). I had a very nasty background noise which messed up the noise level measurement, we're talking about 100uVrms range noise in the audio bandwidth, very low but high enough to ruin my measurements. All was due to a small filter cap at the end of a differential amplifier in the signal chain, once I changed this to a polyester cap the background noise went dramatically low!
Try slipping some bus wire under the cap before soldering, then pull it out to see if you can de-couple the board from the cap. The resonant frequency of the sound should change because the cap you put in is physically bigger. You could also try some GB liquid electrical tape over the cap to see if you can dampen the sound.
Buzzing is not a bug. It's a feature - kindly reminds you to not forget to turn the backlight off. It drains the battery
You should branch out in to ASMR Dave
>_>
Dave jones -soft spoken/ASMR/Chinese filter cap driving an LCD booster circuit
I disagree
+Chris Bourne Heck, yeah! He might gain more audience this way.
Cracking a tinny of Foster's and talking about the piezoelectric effect [AUSSIE ASMR]
I love how hes like "you might be able to hear it" when its louder than the button press annunciator
+tim turner No, it's not, I amplified the audio in editing.
+EEVblog hey can i still get on of your meters?
The whine isn't even louder than the beep in the video. The beep is higher pitch, though. Maybe that's why you perceive it as louder.
+tim turner You would be surprised. Some people are not very sensitive to high frequencies even when age related hearing is taken into account. I remember being able to tell if the TV was on in another room and none of my friends understanding the sound I was telling them it made. I think it's more of the mind filtering noise than it is the ears themselves. My head picks up every little blip and bleep in the world around me.
+tim turner I've always been more sensitive to most when it comes to these sounds too, I can hear CRT TVs when they're turned on (the high frequency noise, not the sounds you're supposed to hear from the speakers) but as I've gotten older, I've discovered I have tinnitus. If you've heard those ringtones that supposedly adults can't hear (this was a big thing back when I was in HS anyway) my tinnitus sounds like that, but not at a super loud level, so it has made it harder to hear some high frequency sound, as I don't know if I'm hearing something or if its just the ringing in my ears.
The line output transformers of older crt pal and ntsc sets oscillated at line frequency 15625 for us in UK with our 625 line 50 frame system. I remember hearing it as a young'n..
Spot on. If you don't specify component grades or tempco values, mfg's will use whatever's on the shelf. They look at footprint, value and voltage rating first when using house parts.
I once worked on a DC-DC switching power supply project that included an over-voltage and reverse voltage protection circuit on the front end. The two circuits worked fine separately, but when combined, the switching frequency of the DC-DC regulator (600 kHz) caused them to couple in a way that made the OV/RV circuit oscillate badly. This caused the two 10uF MLCCs on the input of the DC-DC regulator to scream quite loudly, at a frequency that varied with input voltage. Here's a Dropbox link to a short recording of the sound, as input voltage was varied from 7V to 18V and back to 7V. db.tt/9XAGyHpA (Buzzing MLCCs.m4a, 318kB). This was not amplified during recording; it was clearly and loudly audible from across the room!
Im sure I speak for a few out there.. please do a tear down review of some high end home audio amplifiers! :)
But let those be real high end and not some audiophile bullshit like silver cables.
+ZamaskowanyWolnościowiec Indeed!
+Freshkryp69 I nominate a bryston amp, they are not exactly home audio, but still high end none the less. (they are for recording and mastering studios btw). OR Arcam, that would be interesting as well.
+Freshkryp69 I'd love it - just be sure that you can put it back together. The prices on those things are outrageous!
Mr Carlson's Lab posted a neat video recently about the different types and uses of capacitors, including a bit about the piezoelectric effect
The high pitched whine makes it a genuine EEVblog product.
LOL!
This was way more interesting than I expected. Such a cool channel!! Its motivating me to get back into electronics :)
Another possible fix could be a nice dollop of silicon to cover and dampen the capacitors oscillation frequency, which insistently clashes badly with my tinnitus!!
+Michael Beeny Good idea, that would probably nail it, and much easier than cap replacement
This could be why they put hot glue over the inductor of another Brymen teardown Dave did.
+Michael Beeny Pleasant to me, slightly lower in frequency, almost canceled it out.
+Michael Beeny i done this on various units which have backlights, as they usually tent to produce all sorts of ringing...simply a big silicone drop on top will fix that on 80%...sometimes i use hot glue, as it is stiffer and weakens the ringing a bit more...it depends...
But never use epoxy or alike. if it´s hardened up you´ll never get it off again...and it *amplifies* that ringing tones...
+sporadic -Z Noises like that drive me ever so slightly completely insane :)
1:54 ASMR moment right there.
+rickonami tingles
Fuck me. Dave needs to make videos like that.
Many years ago, I knew a clever engineer who converted ceramic disk capacitors into piezoelectric transducers. I don't know the exact recipe for the conversion but it was something like this. First, he connected many identical disk capacitors in parallel and inserted them into some oil which he heated above the Curie temperature for the ceramic material inside the capacitors. Then he applied a high DC voltage continuously to them as he slowly cooled the oil. Not all the caps performed the same afterward so he sorted through them to select the best ones.
I used to hear the most annoying headache-inducing, nausea-giving high-pitched buzz coming from nearly all small CRT televisions. I haven't heard it in years because these TVs just don't exist anymore, and also because I'm now older I guess and less susceptible to the tones. I do still hear it in certain chargers and I refuse to use chargers that produce sound.. All in all I find it ridiculous that these sort of things are still real issues in modern electronics.
+redtails I miss CRTs.. the sound you mention, the static charge, the ozone smell etc..
I could hear it all the way up here in the states!
When at work:
Skip to @23:09. Pause, set full screen.
Leave workplace, don't turn the monitor off.
+Aaron Stein It's refreshing isn't?
Anyone good with photoshop? I want it in 4k landscape.
Preferably a rain forest as background.
Sounds like my multimeter when using the continuity check function.
when I was in my late teens I could here things that at 48 I no longer can I here. problem is I can still hear lots things I dont want to hear.
Wouldn't it be cool if EEVblog did a video talking about his childhood and when he discovered he was a tinkerer and his introduction to electronics. He may have already done one but I haven't found it. I started taking things apart when I was a kid and between that and the library I had a lot figured out.
He actually made a video just like that, a LONG time ago, back in episode #54
I used to have a Timex Ironman Indiglo watch, that made the same whining noise when the back light was turned on.
interesting investigation, I also had a similar issue on a board with a charge pump ic, same thing, I managed to get much better results with a quality TDK cap but I couldn't make it go away completely. I guess this can only be fixed completely by having a different switching frequency in the charge pump.
That axial inductor (L7) looks like it's part of the piezo sounder drive. One end goes to the collector of a transistor (Q13) and the tracks go off in the right direction.
Just received my BM235 (1st week June 2016). No noise at all.
Great meter, replacing Fluke 117.
I had a digital watch that did the same thing with the lcd backlight. If it was quiet enough (such as waking up at 2am) I can hear it from arms length!
I have noticed this on a lot of my boards. I use ceramic x5r bypass caps and get a click when connecting power or a whine when driving leds with pwm. It only seems to be very noticeable with larger caps (>4.7µF) and packages like 1206 or 1210. The size of the board and location on the board can make a big difference too. The capacitor causes the board to flex, basically turning it into a speaker diaphragm.
Inductor whine can also happen in DC DC converters operating at far over 20khz. If you overload an inductor it can still produce audible tones.
Transformers make 100/120Hz (and harmonics), actually. Same for ferrite inductors: the effect is magnetostriction, which has a square-law response (hence the frequency doubling). This is the magnetic analog of electrostriction, which produces sound in most capacitors (including film caps, just not very much for PP and PET kinds).
Piezoelectricity is a different effect (stronger, self-polarized by nature, proportional), but is indeed present in type 2 ceramic caps. Typical magnitudes for mechanically tapping on a PCB are single to tens of mV, so don't use them anywhere microphony is undesirable!
+Tim Williams YES! I'm a sound engineer and when there's a 100hz Hum my colleagues say it can't be transformers. I was always skeptical about it and now I know why
+Tim Williams Ferrite inductors used for voltage boosting can make very high pitched sounds, like in a joule thief circuit.
MrCarlson's Lab did a video with a nice demonstration of the piezoelectric effect of a generic ceramic cap. Also, I would've tried bodging an electrolytic on there, that should fix the problem completely.
+MrJohhhnnnyyy If you have room?
Hoobie Siamese Yeah, I meant just temporarily whack it in to see which one of the two makes most noise
I can hear a whine from most switch mode power supplies (phone, camera battery, radio,...).
You could have used alligator clips with a steel ball in the jaw tip (from a ball bearing) and isolating the bottom of the clip with electrical tape to jumper power to those pads pretty easily.
"IRONMAN Thriathlon" wrist watches also does make this high pitch sound when you turn on the back light; it's very quiet but if you put it on your ear you can hear clearly...(at least I can!)
The same tone accompanies the backlight on my old Casio G-Shock. It's very very quiet though.
You could tune them to frequency for people with tinnitus . The one you "ruined" had a pleasant tone, 100-200 Hz lower than my own.
Hm. Remembering that rumour about it being possible to hear CPU activity on computers, I now finally see a possible source for the sound. Still *that* bit only will work in James Bond films.
Excelent video, Sire! Most instructive!
My old cell phone used to emit a very high pitched whine, like a CRT whenever I charged it.
Hi Dave, you need a new DMM birthbay cake
you want two mics, one near the meter and one further away, then take the difference in signal. Also, I'd have them equidistant from where you think the noise is coming from, it could potentially be rustling of clothes or other lab equipment.
Wow I just watched eevblog#33 and then you make a video directly related to it a few hours later... spooky.
the thought would be to insulate the part,it may not work,but I would give it a try, being he could change it by pressing on the panel,tells me that the actual part is resonating,yes I would coat it.
I only recently learned about this property of ceramic caps. I have a small tube guitar amp that I did a bunch of switchable mods on (it's an experimental platform) and this explains why one didn't perform as expected. Guess i should stock up on more low value poly's for my experiments and mods.
@EEVblog Hey Dave, could you please make a video going the other way, investigating how vibrations and shock induce a voltage over the capacitor? There's not much available online, particularly comparison between Class 1 and Class 2 capacitors. Class 1 is meant to be much better, but no one shows test results.
I actually found that the high pitch when turning the backlight on was the same frequency as the buzzer, perhaps the buzzer frequency is the same frequency as the charge pump
Awesome Video Dave. Keep up the great work. Nick.
From the looks the capacitor you whacked in there got a much higher voltage rating than the original one. That one was only 6.3 or 10V I guess. So the DC BIAS influence from your cap is most likely smaller which results in a higher effective capacity. That could be the reason for the lower frequency of 3.x kHz you measured.
My UNI-T 60E does a rythmic clicking sound. And even the HP3478A has a continuous very high pitched nearly inaudible whine.
Excellent video, Dave! I thought the money shot was when you zoomed in on the high frequency ringing. 16:26 :)
I was curious if you had considered making an acoustical "sniffer" for ferreting out issues like this. the heart of this would be a tiny electret (ELECTRic magnET) condenser mic element. this can be fished out of a cheap headset they sell for phones. Because the element in all likelihood has an omnidirectional pattern, it will hear everything, and with surprising accuracy to boot. you can use this directly with the audio analyzer apps on your phone, or if you want, you can haywire an op-amp based preamp between the acoustic probe, and your test equipment.
And yes, I agree with you about fan cooled gear. when I'm at work, I am bathed in a virtual sea of white noise.
Not being able to use the Stanford Research Filter, because its fan is too loud, is hilarious.
Thanks Dave, she'll be all right!
When I started my last job I had to work with a device that had a large 24v supply that made a high pitched sound as loud as an airhorn. No one could hear it except me. I'm pretty sure that thing is why I have tinnitus today.
I was hoping you would try to solder that LED to the footprint to see if it would work...
That LED shining out of a window on the back of the unit is almost certainly acting as an optocoupler for some sort of serial data upload. My Uni-T UT61E has a similar mechanism.
Get a Noctua fan for that filter Dave
The EL backlight driver in my old GRiDPad was very noisy...and it had a relatively low pitch to it.
piezoelectic effect of some capacitors are really important. tantalum capacitors are really piezoelectric capacitors. they have e^2x type of characteristic.
No doubt you will notice the fan in the Keithley 2450 SMU when the active load is running...
pretty loud, dave. it's strange--my electric tea kettle has started to whistle at low temperatures. also, when you speak of capacitors making sound, it reminds me of capicator (or condenser) microphones! anyway, i hope you replace/fix customers' meters if the noise is irritating. love u!
Electroluminescent backlights were notorious for making noise.
The waveform and sensitivity reminds me of bifurcations in a driven RLD circuit. The chaotic nature is due to the nonlinear diode's capacitance. They are extremely sensitive circuits, especially with stray capacitance.
Curious how much 'solution' could be had with gobbing the cap with hot-snot as a physical damper to the sound. I'm guessing the board is resonating enough that it would still propagate.
+frollard I had the same thought, I suppose it should at least dampen the amplitude a little bit. It would definitely be an easier fix than swapping the whole cap.
Also, could this be a failure mode in the long run, where caps wiggle themselves loose on the board, especially with the less ductile lead-free solder.
my question is does this tone interfere with the testing capabilities in giving a correct and true reading ?
Yup! The whine is very loud for me!
You should connect it to a spectrum analyzer, it might produce an interesting waveform.
Some of us are very sensitive to high frequency noise and I have thrown things away because they make an annoying high pitched wine. Tenergy makes a great NiMH battery, but their top of the line D cell charger starts screaming the moment you plug it in. I had to move it to my garage. I guess I know what to replace now. I thought it was some kind of voltage converter for the charging circuit.
This is just a normal thing for backlights I remember my old Timex watches with Indiglo(remember that?) would emit this whine.
Dang, that whine would make it really annoying to use that meter. I hope the next batch of meters you have for sale will have that issue fixed.
ok, THIS explains (cant beleive i didn't think ofthis before) BUT those FL Tube SMD style boosters and you get THAT noise!! never figured where this sound came from! ITS SO OBVIOUS to me now! ! LOL Thanks!!
that is the continuity buzzer xD
+Proyectos LED
I see what you did there :)
Had that sht in a pc mouse. It took me a while to find a source. I thought it was a main ic itself. Fixed by placing some electrolytic cap in parallel with input bypass caps. Thanks, good to know the real physical reason behind it.
please do some electronics tutorial videos !
I think the resonant frequency of the human ear canal is actually very close to 3kHz...
18:35 Isn't the blue trace the microphone? So why is it leading the electrical signal? Surely the acoustic delay would mean that the blue trace is lagging the yellow trace?
Thanks for this video Dave, I have a tablet that makes an annoying humming noise like that meter but only if I turn the brightness up, so I'll have to fix that at some point.
Where's the fail button?!?
It seems dielectric of the capaticor is BaTiO3. This substance is both a good insulator and piezoelectric.
Hey Dave !
could you tell me why a manufacturer would put a glob of epoxy instead of the chip on a multimeter board and is there any diference between the two
I want one of your cool blue meters Dave.
You should totally look into the Dell xps as so many of their latest range has horrible coil whine ;[
Interesting analysis. Cool
Also, YAY, finally an electronics video, instead of some teardown or mailbag XP
And also, the audible frequency range isn't exactly dumb. There may be a good reason for it, like losses, switching speed, etc... however yes they very likely could have used a higher frequency ... but, I'm not an IC designer, so yeah there might have been some sort of valid reason.
I have a TI n'spire CAS calculator (a TI-64 on steroids) and it has a color LCD display, I think the resolution is something like 200x300 ish, and when the battery is nearly dead or if the backlight is not at full brightness, it makes similar squealing noises, VERY annoying. I assumed it was an inductor in it part of a small buck-boost converter, I'll see if I can pull it apart and investigate it.
intersting, the ceramic trasducers are used for the sonars and fish finders in the boats electronics, I'm tryng to build a dolphin scare device that way they will stay away from the nets of the fishermans,I was thinking to use the trasducers from the ultrasonic cleaning machines...
I have got an illuminated external keyboard for one of my computers and the keyboard is humming when you turn on the illumination (rather annoying)....
The funny thing is: If you connect a headphone to the computer and turn _off_ the keyboard illumination - you can hear this background humming inside the headphones..... and it goes away when turning the keyboard on.....
Thanks anyways for your wonderful video :)
Could the variations be because of the current sensing? Maybe bumping it changes the conductivity of the battery terminals (or spring connectors), so the pump changes frequencies to keep the output to the back light constant.
did you ever figured out what was that extraLED pad for?
+Jose Santa-Maria isolated interface perhaps?
How about replacing it with a tantalum capacitor?
+sugminpurjo2 That was my first thought too.
Your supposed to call this a "feature".It reminds you the back light is on. :-)
I have an old pager with a display light and when I turn it on it makes the same noise.
I wonder if a dab of silicone on top of the cap would have muffled it?
tell me if i say bullshit BUT:
speed of sound is ~400m/s, one square is 100uS, so une delay of 100uS may be caused by placing the microphone @ 400m/s*0.0001s = 0.04m = 4cm... right?
So im my opinion the peack we see @17:32 should be shift LEFT by ~150us, and that mean the microphone is about 4cm away from the source of the noise.
some serious asmr going on during the whisper part
Could you cover it in hotsnot to suppress the noise?
I had an amplifier that made a buzzing sound when i drove it into a test load, it stopped when i touched one of the ceramic caps.
I had an IBM Thinkpad A31 that would just scream when it was charging. the capacitors/inductors were most likely damaged as it only charged when it was on. That computer was tough as nails, but a pain in the ass to make it charge if the battery was flat.
Do electrolytics do the same sort of thing? I've always wondered about that high-pitched squeal you get from desktop computers, when the caps start to leak.