Products > Test Equipment
USB Decibel Dataloggers?
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Pack34:
Is there a simple datalogger that could be used for decibel level datalogging?

In the past I've often used the picotech TC-08 for temperature, saleae for analog and digital signals, but haven't had the need until now to be able to evaluate noise. For those I would write basic python scripts to execute an action on the product, log all the appropriate data, store the log files, shut down the product, and repeat 100k times.
Tjuurko:
https://www.tekcoplus.com/products/slm25tk
SLM25TK Sound Level Meter with Data Logging Function Measure 30dB~130dB and CD Software
metrologist:
Pack34, did you end up getting a sound level meter? I recently became interested in a data logging sound level meter and the one suggested above is in my list.

The SLM25TK looks like a hybrid of two Reed models in that it has data logging like the R8080 and form of the R8050.

https://www.reedinstruments.com/product/reed-instruments-r8050-sound-level-meter
https://www.reedinstruments.com/product/reed-r8080-sound-level-meterdatalogger

Reed looks like a solid enough meter and the R8080 software looks superior to the SLM25TK (and others), but the Reed R8080 is out of my price range.

I was also looking at the BAFX3608:

https://bafxpro.com/products/bafx-products-decibel-meter-sound-level-reader-w-battery-advanced-sound-meter

The BAFX3608 has sampling rates of 125ms or 1s; the SLM25TK is 500ms or 1s.

The BAFX3608 has 4,700 internal data point storage; the SLM25TK has 32,000.

Amazon reviews seem generally positive for the BAFX, but the one quoted below give me great pause on this unit.


--- Quote ---So, our project is to set up continuous noise monitoring of a neighboring industrial site. On the face of it, this unit seems to have the right features to enable that, although finding that out is not trivial.
1. The software is easy to set up, and it works. You install it and then connect the device over the USB port. One bit of good news is that when the unit is connected to the USB, it runs off of that instead of the batteries, and will stay on indefinitely. Exactly what we need.

2. However, the functionality of the software is marginal at best. While it logs the data successfully, including with a time stamp, there is no way to adjust the rate at which data is collected: it's once per second. Period. So, this means that you will be generating 3600 * 24 data points per day--around 80,000. Of course, you can regularly save the data, but that means that a human has to interact with the device on a regular basis. In addition, the data is stored in a proprietary format, so to actually USE it, you either have to import it back into the software, or, export it to an Excel format. If you should choose to bring it back into the software, then your display options are very limited. (and remember, you probably have 10's of thousands of data points...)

3. However, if you have some skill, you can tackle the project in an entirely different way--this unit has outputs for the data that are labelled "PWM" and "AC". PWM, or pulse width modulation, is very promising because you can bring that into something like an Arduino and log the data that way. You can also adjust the rate at which you take data, whether you do averaging, etc. Very nice. Or, you can pass that data stream into your PC or a Raspberry Pi, and do further processing on it. Maybe even use WiFi to upload to the cloud. All good.

However, to use the PWM, you need to know a couple of things. First, you need to know the frequency of the signals, and secondly, you need to know the voltage level. Of course, neither of these important things is in the manual, so you need to have access to an oscilloscope. We did. So, here is an important element of this review: The frequency is 185Hz. The voltage level is 3.3V.

So, now, you can take this signal into your arduino and log your data. We did this, and it works. As the noise gets louder, the duty cycle increases and knowing the above information, you can calculate the noise level in dB. It works.

4. The AC input, however, is less transparent. The "manual" says that it's a 4Vrms signal. However, we never saw anything like this level. Even with a 70dB input, the AC signal was less than 100mv. So, we don't know if that channel has a failed input or what is wrong. The other thing that we learned is that this "AC" channel's response is dependent on the frequency of the sound that is being measured. Using a signal generator and the oscilloscope, we were able to watch the signal's frequency increase with noise frequency. (And, by the way, it seemed like the amplitude of the measured signal also increased with noise frequency.) So, with a multi-frequency signal (e.g. voice), the output on the AC channel appeared to be noise, but, was the sum of all frequencies in the noise spectrum. So, I guess that if you were to put the device's AC output signal into a frequency analyzer, you could learn about your noise spectrum. Since that was not our interest, we did not pursue it any farther. However, at NO TIME did this signal approach 4V.

5. For us, the final showstopper was when the LCD display failed within two weeks of receiving this unit. Essentially most of the segments disappeared, and could only be brought back by pressing on the front corner of the plastic cover. However, that is not practical, of course, so, even though this unit has most of the characteristics we need, we decided that we had to return the unit.

Bottom line: we can't recommend this unit. It DOES work, and it DOES have the ability to log the data into its proprietary software. The PWM output does work (although we have not done extensive characterization of its linearity, etc.) The AC output does not seem to be useful. And, finally, the proprietary software has severe limitations.
--- End quote ---

https://www.amazon.com/gp/customer-reviews/REYIT01FMN9L4/ref=cm_cr_arp_d_viewpnt?ie=UTF8&ASIN=B00P1D84N6#REYIT01FMN9L4

I think both units need to be calibrated before each use. I found procedure for the SLM25TK:

https://cdn.shopify.com/s/files/1/0393/5153/files/slm-25calibration_of_usb_sound_meter.pdf?v=1657595769

I'm not sure if these devices use a USB to serial data converter cable, but read of several issues of newer Windows not connecting, like the old FT232 issues.

I have not figured out which one to get, and maybe neither, so still looking.

BTW, I want to use the device to monitor band stage conditions, stage/AV room theater projections, sound level for auto exhaust/race track limits, general fooling around, and learning/awareness. Also, for dispute documenting/resolution. No commercial application, so the Reed is difficult to justify.
metrologist:
Well, I found an eBay auction for a Gain Express branded version of a NIB SLM-25 for 28USD and tossed in a bid, and won.
metrologist:
I'm happy with it so far as long as it keeps working. I collected some data and played with the AC/DC output. I guess the DC output would need a PWM filter.

Here is a log of a quiet room, with some scuffling around at first, setting on my laptop



And then some tappy tap tap on my edrums



And then a play at the DC output, low noise, then whistle

 



Whistle
on AC output

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