Cheap Prop 2.4GHz VGA Spectrum Analyzer

DogP

Hey,

I posted a new object: obex.parallax.com/objects/492/ ... it's a 2.4GHz spectrum analyzer using a CYWM6935 module. These are really cheap ready to use 2.4GHz wireless modules w/ trace antennas (and even FCC Approved), which are tunable from 2.400GHz to 2.527GHz. They also have an RSSI register, so you can read the tuned channel's power. That's the basis for this... basically it loops through all 128 channels and draws the RSSI reading out to the VGA monitor. It refreshes at ~5Hz. I added in a peak hold option and a measurement cursor, although they're hardcoded in the code, so you can modify the code to work with whatever interface you want (buttons, RS232, etc).

The module is available from places like Mouser and Digikey for $9.75. Unfortunately it has a 12 pin 2mm header rather than 0.1", so I desoldered the old header and soldered a ribbon cable onto it directly, which I then plugged into a header I soldered to my proto board.

I basically modified Beau's audio spectrum analyzer and SPI demo code to create this, as well as looking at some C code I found online for this module. There's not a whole lot to the project, but I'm debugging some other wireless stuff, and seeing the presence and strength of a signal tells me a lot, as well as making sure I'm not being clobbered by my PC's wifi.

Anyway, I attached some pics, and the object can be downloaded from the link above... let me know what you think and if you have any questions/suggestions.

Pat

Nick Mueller

That's ***really*** geat!
Unfortunately, I don't need one. :-(


Nick

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ElectricAye

Hey,

this is cool! Thanks for posting the object. It's just the inspiration I need right now!

thanks,
Mark



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mikediv

DogP very nice I have been trying to come up with some kind of usable spectrum analyzer myself using the prop but I need to sweep from 10MHZ all the way to 2 Gig + is there a way your code can be modified to sweep the lower frequencies?? because if I understand your design it start sweeping from 2Gig correct?

DogP

mikediv: It starts sweeping at 2.400GHz and stops at 2.527GHz. There's no easy way to modify this to go out of that range, because the IC tunes to the frequency corresponding to the channel selected, and there's only 7 bits. I assume if you try modifying the circuit to go outside that range, the PLLs won't lock and you'll get nothing. You could probably use chips similar to this for other frequencies, like TI's CC1100: http://focus.ti.com/docs/prod/folders/print/cc1100.html ... but that only gets you several bands in the ~300-928MHz range. There may be some 27MHz and 49MHz modules that do this as well. It's nowhere near as good as a real spectrum analyzer, but for the price and simplicity, it's a good tool to have.

It may be possible to use a radio like: http://www.aorusa.com/ar8200.html for something like you're wanting, although I know that RSSI meter on the LCD isn't very precise (only 7 or so steps), but I believe over the RS232 port you can get a more precise measurement, as well as tune across the frequencies you want to sweep.

One other method I had considered was a simple power detector, like this: http://www.minicircuits.com/cgi-bin/modelsearch?model=ZX47-60LN-S+&search_type=info , then use an ADC to determine the power level. You're not gonna get a narrow frequency with that, but if you're just looking for presence of the signal, that may work. Of course that only goes down to -60dBm, and you'd basically be tuning it by installing an antenna at the frequency you're looking for, so sweeping would be out of the question.

Pat

mikediv

DogP thank you for the response and information. I have an Icom 7100 and something called an SDU-100 its a 6809 computer that based on the Icom acts like a spectrum analyzer
it uses the Icom for the freq sweeps and the SDU as the input output, it actually works awesome but it only has a Mono Chrome video output 9 Pin TTL I no longer have any old IBM mono monitors and can get the output to work with VGA or even RGB ,,shame so I have been looking for something else, one of the Parallax guys I think Chris had a design for the prop but I can not find that either lastly I have a Hydra and was hoping to come up with some kind of interface using that but I am new to programing and so far I am quite thrilled with myself for just getting inputs and outputs to do stuff lol
Thanks again still a very nice project you have come up with

Oldbitcollector (Jeff)

This is amazing work! Real Spectrum analyzer's tend to be pricey.

Even if you had to use a few chips to cover common frequencies,
this could become an interesting project board. Maybe something
a few people would be interesting in sharing a small run of PCBs?

OBC

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Ole Man Earl

If you need a 900mhz or a 2.4ghz spectrum analyzer, a company called Ubiquiti has them for >>> $39.00 <<<
Hard to believe but I got one for my wifi stuff and it works great.
Thought I would pass this along.
Earl

http://www.ubnt.com/airview/

DogP

Mike: I'm not familiar with either of those systems, but as you gain experience w/ the prop, you may be able to replace the SDU-100 w/ a prop and display it to a TV/VGA monitor.

OBC: I've been thinking about something like that, although I'm not sure if it'd be worth the trouble/cost. Using several chips with different RF front ends for the different frequencies may get pretty ugly, and probably for a little more, you could make something MUCH better.

Earl: Cool... I hadn't seen that specific one, although of course the point for this project was to make something cool .

Pat