Siglent SDM3065X Low Buzzer Volume Repair/Hack Attempt

[Kleinstein]

The piezo buzzers in smoke detectors are usually on the large and loud side.
To get a really loud tone it also helps to drive them at there resonant frequency. This can make a huge difference in the sound level.

[tautech]

The piezo buzzers in smoke detectors are usually on the large and loud side.
To get a really loud tone it also helps to drive them at their resonant frequency. This can make a huge difference in the sound level.

Is that normally stated in their datasheets ?

[KungFuJosh]

The piezo buzzers in smoke detectors are usually on the large and loud side.
To get a really loud tone it also helps to drive them at their resonant frequency. This can make a huge difference in the sound level.

Is that normally stated in their datasheets ?

That datasheet (attached) for the buzzer I linked above states the 85dB pressure level at 2.4kHz and 10cm distance. I assume they do that at the resonant frequency to get a higher dB rating. Just an assumption though. 🤷

[tautech]

The piezo buzzers in smoke detectors are usually on the large and loud side.
To get a really loud tone it also helps to drive them at their resonant frequency. This can make a huge difference in the sound level.

Is that normally stated in their datasheets ?

That datasheet (attached) for the buzzer I linked above states the 85dB pressure level at 2.4kHz and 10cm distance. I assume they do that at the resonant frequency to get a higher dB rating. Just an assumption though. 🤷

A quick study reveals output noise is related to drive voltage but offers no further graphs of frequency vs output levels.
Maybe the OEM buzzer can provide sufficient output noise @ higher drive voltages.

[Kleinstein]

Attached is a datasheet that shows a frequency response. It shown a sound level some 15 dB high at resonance. That is quite an audible difference.


edit: added a 2nd data-sheet for a piezo buzzer. The first was a magnetic.

[t1d]

Attached is a datasheet that shows a frequency response. It shown a sound level some 15 dB high at resonance. That is quite an audible difference.


edit: added a 2nd data-sheet for a piezo buzzer. The first was a magnetic.

Thanks for joining in and sharing your expertise, Kleinstein!

Tautech had pointed out that
1) the original location, of the original buzzer (it being just a piezo wafer,) was over the digital board,
2) the new location (tucked into the plastic front cover, outside of the case's metal front bracket) will cause the cable to be routed past the front analog board,
3) but if proper coax wire was used, this should not be much of a problem. (However, again, we were discussing using a piezo wafer.)
So, the two types of Buzzers brings a question to mind... Will a magnetic type create any greater, or worse type of, ambient noise?

The question arises for me, based on my thinking that Electromagnetic buzzers are made from a metal sounding plate that is flexed by oscillating an electromagnet to drive it. Do I have that correctly? If so, I would think that electromagnetic types would have very different ambient noise considerations than plain piezo wafer types.

As for the resonant frequency/volume/data sheet question... I believe, that you have it correctly - That buzzers are specified in their data sheets at their highest resonant frequency, which brings about their greatest volume, at their stated typical operating voltage. Additionally, a range of frequencies is stated for a range of operation voltages. It also appears to me that piezo wafers will sound over a range of driving frequencies and voltages, however both factors seem to effect output frequency and volume.

I did get some sleep, but - warning - that may not improve my brain fog = grin.

[t1d]

Here's the socket that I installed in place of the original buzzer. It is kin to a Dupont socket. The two outer sockets are for the active pins. The remaining interior sockets have had their pins removed. This makes for more surface area, with which to secure the fixture. The caulk blob is proper electronics grade e-cap caulk.

My parts are scheduled to be delivered tomorrow.

[t1d]

The buzzers have arrived. I am not feeling like working with them, too much, but I was able to make theses quick observations...

CMI-1295-05TH
I think Josh noted that the canister might be a hair wide, on the dimension across the flats, to fit completely into the barrel of the probe socket. This is true. The canister is about 0.5mm too wide.

Josh also mentioned that the side of the canister might be sanded off, to make it fit. I have my doubts that this could be done, without breaching through, because the buzzer's walls are particularly thin.

However, I do believe that the this buzzer could easily be glued to the top of the flats. There does appear to be room between the top of the flats and the metal front case bracket. No guarantees = You will need to do your own measuring.

Additionally, the question about the ambient noise created by this type buzzer (magnetic) has not been sorted out.

PKLCS1212E2400-R1
This buzzer is a piezo type, so there is no compatibility issue. At 12x12x3mm, it fits nicely across the flat top of the probe socket hole.

However, there are a few points to consider in mounting it.
1) The sounding hole is on the same side as the pin pads (Blue arrows.)
2) The sounding hole is offset from the center to the edge (Red arrow.) The socket hole has room to align the sounding hole fully in the opening, but care will be needed in seating the case. Gluing it in would be simple enough.


The Original Buzzer
I sized it up, a bit more. I still believe that it will fit within the open space in the plastic face plate. But, you will need to confirm this for yourself.

Next Step
I am liking the PKLCS1212E2400-R1 best of all, as far as mounting a buzzer is concerned. I will do some sound level tests with it. If it is acceptable, I will likely give it a try.

[t1d]

PKLCS1212E2400-R1
This buzzer is a piezo type, so there is no compatibility issue. At 12x12x3mm, it fits nicely across the flat top of the probe socket hole.

However, there are a few points to consider in mounting it.
1) The sounding hole is on the same side as the pin pads (Blue arrows.)
2) The sounding hole is offset from the center to the edge (Red arrow.) The socket hole has room to align the sounding hole fully in the opening, but care will be needed in seating the case. Gluing it in would be simple enough.
(Attachment Link)

Well, here is a silly question - I can't find what I consider to be a traditional indicator for the positive pad. No "O" indention in the plastic. No silkscreen "+" mark. Nothing in the data sheet.

There is a square painted over one of the pads. Do you think this is the positive pad?

Edit: Now, I feel even more silly... Because, all I needed to do was test the continuity.

The silkscreen square indicates continuity to the metal side of the piezo wafer. This is the ring, on the ceramic side of the wafer. And, it should be connected to the negative leg of the original buzzer circuit. Ahh... That feels better = grin.

[KungFuJosh]

If it turns out you like the buzzer I chose, the easiest thing to do would be to sand or (very carefully!) drill the flat edges of the socket hole flats. 0.5mm is practically nothing.

That's how I would do it anyway, but I don't care about modifying the plastic as long as it isn't visibly damaged. 😉

[t1d]

I forget the frequencies of the three volume settings. I need that information for testing. I searched for it, but didn't find it in the manual, programming guide, this forum, the web, etc. Does anyone recall?

[tautech]

I forget the frequencies of the three volume settings. I need that information for testing. I searched for it, but didn't find it in the manual, programming guide, this forum, the web, etc. Does anyone recall?

It was added in firmware V3.01.01.07 March 2020.
Dunno if anyone has recorded it. 

[KungFuJosh]

I forget the frequencies of the three volume settings. I need that information for testing. I searched for it, but didn't find it in the manual, programming guide, this forum, the web, etc. Does anyone recall?

Do you have a scope or a frequency counter?

[t1d]

I forget the frequencies of the three volume settings. I need that information for testing. I searched for it, but didn't find it in the manual, programming guide, this forum, the web, etc. Does anyone recall?

Do you have a scope or a frequency counter?

Yes, however, my DMM is still disassembled. I thought I saw where someone had listed the frequencies, here, on EEVBlog Forum. But, I didn't find them anywhere.

[KungFuJosh]

Yes, however, my DMM is still disassembled. I thought I saw where someone had listed the frequencies, here, on EEVBlog Forum. But, I didn't find them anywhere.

It needs to be a little bit disassembled for you to connect probes to the buzzer connections. 😉

[t1d]

There is an unused, threaded, mounting hole, adjacent to the original buzzer location. See Red Arrow. Its pad is common to Case/Earth GND. It would be a very convenient tie point, for the new buzzer's cable's metal, woven shield. Is there any reason to not use this mounting hole? (I can't imagine any issues. However, I am being extra cautious with this project, as it is a precision instrument.)


I made some very pretty plug cables, tonight, for the new socket. I had not thought of the grounding point, proposed above, when I made them. So, I trimmed off what I thought would be the unused extra shield wire, because I was thinking of picking up the case ground at another less convenient location. Doh.

I guess I can save these pretty cables to make probes. I am glad that I bought plenty of wire, to make up for mistakes. Such mistakes come with the (uncharted) territory, when you are breaking trail and building as you go.

[Kean]

Resistor values are both 810R, but, both of my resistors measured 1K, in circuit.

Just catching up on this thread and I see you mentioned several times that the resistors are 810R but measure 1k.
From the photo I can see that they are in fact 1k resistors and marked with the EIA96 code "01B" which is for 1k00 1%.
https://en.wikipedia.org/wiki/Resistor#EIA-96_marking

[t1d]

Resistor values are both 810R, but, both of my resistors measured 1K, in circuit.

Just catching up on this thread and I see you mentioned several times that the resistors are 810R but measure 1k.
From the photo I can see that they are in fact 1k resistors and marked with the EIA96 code "01B" which is for 1k00 1%.
https://en.wikipedia.org/wiki/Resistor#EIA-96_marking

Hi, Kean. That is excellent information and something that I was not aware of! Thank you! I hope you will continue to come along with us on this project. I need all of the help that I can get = grin... Cheers.

EDIT 1: Thanks, Kean; I looked at the link. It is a very interesting numbering system. Yep, I did not know about this one, at all. Very helpful! More cheers...
EDIT 2: Schematic updated at post #5.

[t1d]

Life threw me a curve ball... I have had to put the project on hold, as I must move. The rent went up.

Here is a video that has some important information about how to mount a bare wafer. Basically, you can not leave it "flapping in the breeze." It must be affixed.