Homebrew Digital Sampling Audio spectrum analyser.

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#61
G.Kleinschmidt said:

Not too many crystals cut for audio frequencies though!
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The HP 3581 uses crystal filters, 3 to 300 Hz BW. I think that it has a 100kHz IF and a VTO of 1.0 to 1.5 MHz. Time was when you could buy an HP3581 for $20, now they go for hundreds of dollars.

I have not yet worked with their chips, but I would imagine that the clock-through is going to require some post-filtering. MSI has some white-papers on their website which might be a bit more revealing.

You know, you can always use some programmable potentiometers for very quiet bandpass filtering -- use some JFETs for switches for the range (decade) capacitors. Analog Devices has an application note on the potentiometer part of this up on their website.
 
#64
jackinnj said:
I'm not a big fan of Maxim -- although I've used their DAC's and ADC's and the ubiquitous MAX232 -- they just obsolete parts too quickly. One of their switched cap filters costs as much as the MSI which does the job of six.

MSI also makes energy scavenger products. Neat!
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Well, I have myself no warm feelings for Maxim's business practices, however they are very good for DIYers; they'll ship you for free 15pcs of almost anything they currently have in production.

OTOH, are you sure MSI is there to survive for long in a very competitive market?
 
#65
jackinnj said:


The HP 3581 uses crystal filters, 3 to 300 Hz BW. I think that it has a 100kHz IF and a VTO of 1.0 to 1.5 MHz. Time was when you could buy an HP3581 for $20, now they go for hundreds of dollars.

I have not yet worked with their chips, but I would imagine that the clock-through is going to require some post-filtering. MSI has some white-papers on their website which might be a bit more revealing.

You know, you can always use some programmable potentiometers for very quiet bandpass filtering -- use some JFETs for switches for the range (decade) capacitors. Analog Devices has an application note on the potentiometer part of this up on their website.
Click to expand...


OK, but that HP is a sweeping frequency analyzer, like my SA200K, which also uses crystal filters. The VGA unit is a different kettle of fish, however.

I like the idea of a 60 band unit for the MkII VGA version, so that MSI chip with 6 channels per DIP is looking like the best option so far. Still don't know what they cost though and still haven't received a reply from MSI. Time so send another email.

Cheers,
Glen
 
#67
Great project!

Hi Glenn,
What a great idea!

I'm using an HP 3585A and have a broken 3580A to fix. I'm thinking that if you can output the data to a computer, you can then measure frequencies and levels very accurately. This also gives you the ability to document your other projects in great detail. That is one of the more difficult aspects of using the older gear.

Your first idea was really cool. I'll watch the second project you have decided to go with (I liked your first idea better). Also, it gives some practice with programming PIC devices. Nothing wrong there.

The newer DSO products do not do FFT very well unless you get into the more expensive products (I'd be extremely happy with an Agilent DSO-6000 series). Both noise and resolution are problems. Also, they are almost all 8 bit and I suspect you could get higher resolution with your focused design.

Good going!!

Best, Chris
 
#68
Re: Great project!

syn08 said:


Apparently, $5.95 in 1000's. Which probably translates to $10-12/pc.

http://eepn.com/Locator/Products/ArticleID/34624/Action/Issue/34624.html
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Hmm... OK. That's not too bad, so long as I don't have to buy 1000......


anatech said:
Hi Glenn,
What a great idea!

I'm using an HP 3585A and have a broken 3580A to fix. I'm thinking that if you can output the data to a computer, you can then measure frequencies and levels very accurately. This also gives you the ability to document your other projects in great detail. That is one of the more difficult aspects of using the older gear.

Your first idea was really cool. I'll watch the second project you have decided to go with (I liked your first idea better). Also, it gives some practice with programming PIC devices. Nothing wrong there.

The newer DSO products do not do FFT very well unless you get into the more expensive products (I'd be extremely happy with an Agilent DSO-6000 series). Both noise and resolution are problems. Also, they are almost all 8 bit and I suspect you could get higher resolution with your focused design.

Good going!!

Best, Chris
Click to expand...


Thanks Chris.

I'm actually going with and building all the designs detailed here. All will go up on my webpage eventually. It's just taking me ages because it's such a tedious process.

Cheers,
Glen
 
#71
jackinnj said:
Glen:

We are expecting something like this:

http://www.youtube.com/watch?v=2gKk_hcp8Vw
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Neat, though I think my VGA display is going to look much cooler than that 🙂

Anyway, was occupied mainly with home maintenance stuff this weekend, but I did manage to knock off the complete band pass filter and peak detector board layout in the evenings.

I have revised the design slightly from 20 bands to 21 bands, as 21 half octave bands is a better mathematical fit into the compete audio (20Hz-20kHz) frequency spectrum.

Top layer:
 

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#72
.....and the bottom layer.

One BC548, one BC558, 16 quad opamps (TLO74), 23 schotkey diodes, 143 capacitors and 300 resistors.

Bandpass Fc's are:

20Hz
28Hz
40Hz
57Hz
80Hz
113Hz
160Hz
226Hz
320Hz
453Hz
640Hz
905Hz
1.28kHz
1.81kHz
2.56kHz
3.62kHz
5.12kHz
7.24kHz
10.24kHz
14.48kHz
20.48kHz


Cheers,
Glen
 

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#75
Spent a couple of hours getting further with soldering bits into the prototype board for the digital logic video generator board this evening.

Spent most of my time beefing up the ground tracks on the underside of the board with heavy gauge wire and revising supply rail decoupling to get the 40 nS LM360 comparator working in its socket without oscillating.
The LM360 does the input voltage / exponential ramp comparison to generate the video signal for the amplitude level bars.
I was successful in the end, which really is amazing considering what a rats nest this prototype is. I almost finished the video blanking circuitry as well.
So far the design, which I completed entirely on paper, is working 100% as predicted 😀

Here is a short 20-second video I made with my digital camera of the VGA display at this nearly completed stage (3 meg download):


http://users.picknowl.com.au/~glenk/VGAASA1.AVI


Note that I haven’t built the analogue band filter / peak detector board yet, so the display is so far still a little bit boring. None of the 21 amplitude bars will appear on the screen until their voltage inputs are stimulated.

For this demo I just wired in the potentiometer into one of the 21 inputs as I did before, to get one of the amplitude bars to appear on screen.

The yellow amplitude bar is dancing up and down in the video because I was twiddling the pot.

I still have to finish soldering in the video blanking logic for the graticule generator section. I currently have the vertical blanking operating on the horizontal graticule lines only. The vertical blanking for the vertical graticule lines still needs to be done, as does the horizontal blanking for both the horizontal and vertical graticule lines. When done, the graticule will consist of just the 21 by 10 square grid in the middle of the screen.

Cheers,
Glen
 
#77
janneman said:
Yes, it's a different thing. While I was reading your stuff I was also looking for info on the HP3577, thus I mixed the two up.

Nice project you have going there; you're a man of many talents!

Jan Didden
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Jan -- have you hooked up with the HP/Agilent group at Yahoo -- there us an enormous reservoir of talent?

I have been playing with a USB based GPIB adapter for my HP3577.
 
#78
jackinnj said:



Jan -- have you hooked up with the HP/Agilent group at Yahoo -- there us an enormous reservoir of talent?

I have been playing with a USB based GPIB adapter for my HP3577.
Click to expand...


Yes I know that Yahoo group.

How are you getting along with that USB adapter? I had one to try out but couldn't get it to work. I ended up buying an NI 488 card on eBay.

Jan Didden
 
#79
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