DIY Microprocessor Sound Level Meter Demoed At MIT

An anonymous reader writes "A Piezoelectric Sound Level Meter was demoed at MIT's Battle of the Bands last month, borrowing its display from the do-it-yourself USB LED marquee that was the subject of a previous Slashdot story. This video tutorial describes in detail both the analog electronics plus the C code that runs the system. If this is your first experience at the intersection of digital and analog systems, don't be scared!"

Comments

Get rid of the micro - LM3914

[marcop]

LM3914 can handle 10 LED's per chip and can be cascaded for more. Add an amp for signal conditioning on the front end, and then hookup lots of LED's per line if you use a transistor to drive a bank of LED's.

They need a micro because their display is too complex for the job. But, make the display simple and you can make the whole design simple. Yet, since this is MIT's it has to be complex for some reason.

Re:Get rid of the micro - LM3914

[marcop]

You're right, if you want advanced features then you have to include a microcontroller. Although I have used the LM3914 with a CD4538 per line to do peak level indication. If you want to only do peak level indication for the upper few lines then this would be easy enough. However, doing more than a few lines and doing other stuff you mentioned then of course a microcontroller would be easier.

Point is there are many ways to do this simple project, and it is beyond what should be showcased by MIT and here on slashdot. How about doing something a little more interesting like audio spectrum by having the micro also do FFT? If you cram all these features into the project then perhaps I would make it slashdot worthy. But as is it is far from it.

Re:A CPU for this?

[porl]

you may not find the lower level components interesting, but some people do. being interested in vintage amplifiers means that i am somewhat interested in what makes various older components sound the way they do. this led me to learn about the different characteristics of varying types of capacitors, which led me to trying to make my own capacitor out of foil and cling wrap. it certainly wasn't anywhere near the quality of a commercial capacitor, and even fell apart after being moved around too much, but it worked and i really enjoyed it and learnt from it. that doesn't mean i would want to try to rebuild a computer mainboard with diy capacitors (although i would certainly tip my hat to someone who pulls that off) but i don't see it as a waste of time in the slightest.

to each their own i guess.

I expect better from MIT students.

[Animats]

Yes. These are MIT students, remember. Now, if they designed something simple that got the same results as a properly calibrated A-law sound level meter, that would be useful. Or, for example, they could use the microprocessor to do an integrating dosimeter calculation, so you know when you've overdosed on live music. That would be useful to do cheaply, because noise dosimeters are still expensive, over $1000.

Re:iPhone App

[Anne Thwacks]

response curve of the built-in microphone. Surely that would color the spectrum analyzer?

That would have to be the easiest thing in the world to compensate for!

There might be firm limits to the top and bottom of frequency response set intentionally to limit the bandwidth intentionally (wide bandwidth is not good for telephony), but I expect these to be done in software to guarantee sharp cutoff.

I had in mind a recording RTA application. Sound techician could compare acoustics of different locations/PA rig setups/EQ settings,

Being able to e-mail a recorded sound spectrum to the lab for interpretation might be useful to all manner of people. (Cant reveal more - they might shoot me!)

Re:Ho-hum

[hey!]

Well, you should go one step further and ask, why build something like this at all when you can buy a finished product for less, if you count your time worth anything?

The reason to use the piezo buzzer is simple: you've got one in your parts box and you're curious what you could do with it besides make a buzzing sound. It's like what somebody said about dogs who've been trained to walk: it's not that they do it well, it's that they do it at all.

With respect to the use of a single transistor, that's educational. Yeah, you can get a better IC amp, but then you can buy a better finished device. You learn something different by using discrete components. Of course, you could do a more elaborate discrete amplifier, but then you put off the satisfaction of seeing the blinken' lights that much longer.

Years and years ago when I was at MIT, there was a kid who commuted to campus in a homemade electric car. It wasn't a very good car. For the money and effort he put into it, he could have bought a cheap gasoline car and tinkered with that. For that matter, I don't think his car was much better than a bike. The same kind of arguments you are making could apply to that.

When, other than when you are learning, can you do something differently than by the book, just for the fun of seeing it work?