EEVBlog Rebranded Brymen BM235 & Backlight noise research

[wraper]

http://www.kemet.com/Lists/TechnicalArticles/Attachments/62/2007%20CARTS%20-%20Reduced%20Microphonics%20and%20Sound%20Emissions.pdf
not a single word about resonance.

[markone]

not a single word about resonance.

So those capacitors are flat response wideband speakers ? 

[wraper]

not a single word about resonance.

So those capacitors are flat response wideband speakers ? 

seems like that

[markone]

not a single word about resonance.

So those capacitors are flat response wideband speakers ? 

seems like that

IMHO i do not think so, i'll bet they sound only in high freqs due to small mechanical dimensions.
Anyway, that's not the point,  let's wait for some waveforms screens.

[wraper]

IMHO i do not think so, i'll bet they sound only in high freqs due to small mechanical dimensions.
Anyway, that's not the point,  let's wait for some waveforms screens.

check out the graphs on the second last page.

[Brumby]

... i'll bet they sound only in high freqs due to small mechanical dimensions.

I agree.

Resonance isn't necessarily relevant here and the explanation for the phenomenon does not require it - so I don't think we need to spend any more time jumping around in that blow-up castle.

[idpromnut]

Not sure how important it is to the discussion, but I captured a couple of (crappy) waveforms at both C44 and C43 showing both the fundamental ~32kHz drive for the charge-pump (on C43), and the ripple on the output (C44).

[markone]

Not sure how important it is to the discussion, but I captured a couple of (crappy) waveforms at both C44 and C43 showing both the fundamental ~32kHz drive for the charge-pump (on C43), and the ripple on the output (C44).

32Khz are well above human hearing capabilities, i guess you are listening to the tone deriving from square wave burst repetition period, if read well your screen should be around 4Khz.

Also my Oregon Scientific alarm clock emits whining noise with backlight turned on,  but i can live with 

[idpromnut]

Not sure how important it is to the discussion, but I captured a couple of (crappy) waveforms at both C44 and C43 showing both the fundamental ~32kHz drive for the charge-pump (on C43), and the ripple on the output (C44).

32Khz are well above human hearing capabilities, i guess you are listening to the tone deriving from square wave burst repetition period, if read well your screen should be around 4Khz.

Also my Oregon Scientific alarm clock emits whining noise with backlight turned on,  but i can live with 

Without C44, there is no 4-5kHz repetition period; I'm not sure if it is the 32kHz itself I am hearing or some harmonic of it, but it is very very high pitch, right at the limit of my hearing. It is similar to the whine that I heard with older CRT-based TVs.  Not sure if that is in the same frequency range, but that is the closest that I can describe it.  Either way, that high frequency noise is very attenuated so I'm not bothered by it, especially with the case closed.

[markone]

...I'm not sure if it is the 32kHz itself I am hearing or some harmonic of it, but it is very very high pitch, right at the limit of my hearing. It is similar to the whine that I heard with older CRT-based TVs.  Not sure if that is in the same frequency range, but that is the closest that I can describe it.  Either way, that high frequency noise is very attenuated so I'm not bothered by it, especially with the case closed.

It's highly unlikely, i would say almost impossible, that you are able to hear a 32Khz tone or its harmonics (that would be even higher), CRT noise's pitch freq. was on par with horizontal scan rate, around 15-16Khz depending on TV standard (PAL, SECAM, NTSC).

Anyway considering the amount of time that normally one spend with DMM backlight turned on, this does not seem a trouble at all.
 

[Scottjd]

...I'm not sure if it is the 32kHz itself I am hearing or some harmonic of it, but it is very very high pitch, right at the limit of my hearing. It is similar to the whine that I heard with older CRT-based TVs.  Not sure if that is in the same frequency range, but that is the closest that I can describe it.  Either way, that high frequency noise is very attenuated so I'm not bothered by it, especially with the case closed.

It's highly unlikely, i would say almost impossible, that you are able to hear a 32Khz tone or its harmonics (that would be even higher), CRT noise's pitch freq. was on par with horizontal scan rate, around 15-16Khz depending on TV standard (PAL, SECAM, NTSC).

Anyway considering the amount of time that normally one spend with DMM backlight turned on, this does not seem a trouble at all.

I guess it depends on your application. For videos I tend to use the fluke because I can adjust the backlight to be on up to 30 minutes. This isn't because it's dark, but the backlight help the display he captured over the studio lights. So the 10 minute backlight is a nice feature for me to have when I need two meters measuring separate parts.
Dave has mentioned that this is intermittent and not all meters are as loud as mine or idpromnut's meter. It just happens that we released the first reviews on the meter. He also said that Brymen is looking into it.

I was way to tired and still recovering from a hostilely procedure to do any probing or take any measurements, thanks for idpromnut for taking those readings. I may go back to that if I have time and take some measurements. The irony is the 235 was very acurate for taking mA readings, but I think my fluke and hp bench should be able to take the same.

If I had to guess the only reason these additional component are inline with the LED back light is to support the flashing on and off with the continuity feature. Most of my other cheaper meters don't have any filtering before the lighting like this one has. But they also don't flash on and off, or habe a backlight that stays in for 10 minutes. They are more 10 second lights.
I think I'll wait it out and see what Brymen comes up with after they finish researching. If they need one that is loader then normal I can always ship mine in for an exchanged unit. I'm always willing to work with companies that listen to their customers and are willing to spend time to improve their products.

[idpromnut]

If I had to guess the only reason these additional component are inline with the LED back light is to support the flashing on and off with the continuity feature. Most of my other cheaper meters don't have any filtering before the lighting like this one has. But they also don't flash on and off, or habe a backlight that stays in for 10 minutes. They are more 10 second lights.

I think this was more a case of following the application notes for the LCD driver chip (which I mistakenly thought was the DMM frontend). You can see here in the datasheet on page 14 (http://www.hycontek.com/attachments/LCD/DS-HY2613_TC.pdf) that there is an output filtering cap (4.7uF). So nothing to do with the flashing backlight (indeed, the backlight "flashes" at a very low frequency, say about 10Hz max, so it should not be affected by a 32kHz ripple at all).

[mos6502]

Strange decision to use a switch mode LED driver. Doesn't the electrical noise affect the measurement? On the UT139C, the LEDs are simply connected to battery voltage via a resistor and switched to GND with an NPN transistor.

[ve7xen]

Strange decision to use a switch mode LED driver. Doesn't the electrical noise affect the measurement? On the UT139C, the LEDs are simply connected to battery voltage via a resistor and switched to GND with an NPN transistor.

Meter is powered by 2xAA batteries. Nominal voltage is 3V but should expect it to work down to 2.2V or less. Most white LEDs have Vf greater than this, and there may be several in series. A switcher is needed. It should not affect measurement if designed properly.

[mos6502]

Strange decision to use a switch mode LED driver. Doesn't the electrical noise affect the measurement? On the UT139C, the LEDs are simply connected to battery voltage via a resistor and switched to GND with an NPN transistor.

Meter is powered by 2xAA batteries. Nominal voltage is 3V but should expect it to work down to 2.2V or less. Most white LEDs have Vf greater than this, and there may be several in series. A switcher is needed. It should not affect measurement if designed properly.

The UT139C is powered by two AA batteries as well. Funnily, the manual says that the backlight may stop working as the batteries discharge. 

Still, this could easily be fixed by replacing the LEDs with amber ones (Vf=1.8V). Looks better anyway, no unnecessary complexity and no acoustic noise. But apart from that, the switcher does have an effect. Even if it doesn't interfere with the multimeter's measurement itself, it could interfere with a sensitive circuit that is being measured. I mean, if you hold an AM radio next to the meter, I'm sure you're going to hear the noise from the switcher.

[EEVblog]

Strange decision to use a switch mode LED driver. Doesn't the electrical noise affect the measurement? On the UT139C, the LEDs are simply connected to battery voltage via a resistor and switched to GND with an NPN transistor.

Meter is powered by 2xAA batteries. Nominal voltage is 3V but should expect it to work down to 2.2V or less. Most white LEDs have Vf greater than this, and there may be several in series. A switcher is needed. It should not affect measurement if designed properly.

Yes. And this is why some older meters have green backlights, lower voltage drop so can direct power from 2 1.5v cells

[vsboost]

Mine is barley audible, literally have to put my ear to the meter to hear it, and yes my hearing is perfect.

[boggis the cat]

Mine is barley audible, literally have to put my ear to the meter to hear it, and yes my hearing is perfect.

The one I got seems to be fairly quiet, too.  Seems quite a high frequency, so possibly my aging hearing doesn't perceive it well.

Edit:

Used the iPad to record the noise.  It is a reasonable spike, at a bit over 10kHz.

[EEVblog]

Just shot a video on this, editing now.

[Scottjd]

Just shot a video on this, editing now.

Thanks for the video, I was debating on swapping the cap after idpromnut confirmed that C44 as the noise maker.

I didn't want to probe or trace anything since I didn't want to affect the acuracy or warranty of the meter. I know continuity feeds a voltage, and I feared that voiding the warranty. I know not all of them are as loud as mine, I didn't have to turn up the gain on my mic and it probably from different manufactured capacitors like you said. But I think I'll forget about the warranty and replace the cap. I purchased a microscope with a camera a last month and I've been wanting to try it and see how good it records video, so I think this cap replacement will make a good test for the microscope camera. After all, it was originally going to be a gift so if I screw it up I still have two other meters I fully trust.

Unfortunately I don't have any new ceramic 10uF caps, I only have up to 1uF. So I'll probably pull one from a scrap board. I do have some 1206 tantalum caps but not any ceramic.

I also had the idea of just re-flowing the cap it came with. I started to wonder if the vibration could be amplified from a weaker solder joint, and if that's the difference between meters also?
Unlike yours in the video, I can't get my sound to change by touching the meter and it doesn't sound shakey. Mine seems to be a constant steady frequency. So when I saw your sound can change by touching the meter I wondered if the sound is being amplified off the board, and maybe re-flowing it would turn the volume down?

I was more couriose of the LED, that's why I decided to take it apart. I've built 30+ LED flashlights with different LEDs and drivers, all with different programmable features and power outputs and never heard a noise that louad with LEDs.

I'm going to stay with review videos and not fix videos. I know I'm new at the fixing and learning the electronics side. I try not to do tear down videos despite that I've torn down a lot since I was a kid, but I don't have the reverse engineering skills or understanding of electronics to explain it like you do. That's the part I just started teaching myself in my spare time as a new hobby. Building a soldering with batteries and RC stuff I've been doing since a kid, but that doesn't mean I fully understood how the electronics worked.

[idpromnut]

I didn't want to probe or trace anything since I didn't want to affect the acuracy or warranty of the meter. I know continuity feeds a voltage, and I feared that voiding the warranty.

We're talking about Dave here... he sells T-Shirts with the logo "Warranty Void if Not Removed!"  Also, regarding the continuity tester: if you're worried about the voltage it feeds into the circuit under test, then THAT is an /excellent/ video to shoot as to whether it will or will not matter!  Hint: it probably will be just fine, now your turn to figure out why!

[Scottjd]

I didn't want to probe or trace anything since I didn't want to affect the acuracy or warranty of the meter. I know continuity feeds a voltage, and I feared that voiding the warranty.

We're talking about Dave here... he sells T-Shirts with the logo "Warranty Void if Not Removed!"  Also, regarding the continuity tester: if you're worried about the voltage it feeds into the circuit under test, then THAT is an /excellent/ video to shoot as to whether it will or will not matter!  Hint: it probably will be just fine, now your turn to figure out why!

Ahh yes, this I know. His manual even says he encourages you to take it apart. But taking it apart and probing around, well I view that differently. As for diagnosing and probing  I'll leave that to your and Daves channel. I have 3 things on my bench to review still from vendors and 6 personal items I bought that I want to review. So I'm a little backed up on the reviewing side. My health has backed me up in the schedule for reviews and life in general so unfortunately this takes away from the learning electronics hobby time slots.

But if I get around to it I'll be sure to report back. Thanks for proposing the challenge.
I probably could have traced the inductor, but didn't think about it. Oh well, to late.

[Scottjd]

Just shot a video on this, editing now.

I also had the idea of just re-flowing the cap it came with. I started to wonder if the vibration could be amplified from a weaker solder joint, and if that's the difference between meters also?
Unlike yours in the video, I can't get my sound to change by touching the meter and it doesn't sound shaky or muddy. Mine seems to be a constant steady frequency. So when I saw your sound can change by touching the meter I wondered if the sound is being amplified off the board, and maybe re-flowing it would turn the volume down?

So the curiosity about this question I asked myself got the better of me and I decided to do some experimentation and find out the answer. Besides I was wanting to try out my new microscope anyway. This is not what I should be doing, I should be reviewing some other items but sometimes I get stuck on curiosity with one item and need to answer that one question before I can move one.
So I guess I answered my own question....... and now I can move on......

https://youtu.be/TfNuTmqtiD4

[NilByMouth]

Got to thank Brymen for designing a meter with an inherent design fault. So much more fun than if they'd designed a perfect meter without any problems.

[Scottjd]

Got to thank Brymen for designing a meter with an inherent design fault. So much more fun than if they'd designed a perfect meter without any problems.

It's still a great meter. I don't have anything as acurate as this under $400 US, and I think this was a little over $100. Hands down, can't beat it even if you get one with a loud backlight. I would still recommend it.
But now maybe Brymen and stop looking into why some are louder then others and just change the design to have a bigger capacitor.