Re: Real Life Beamforming with substandard arrays. Need help forming some sort of solution.

Phil Winder wrote:
On Jun 26, 4:28 pm, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
Phil Winder wrote:

[...]

@Rune: Ah yeah, never thought of it that way. Well you could argue
that the spreading in the pulse is in some part due to multipath.
That will only affect the temporal resoultion, so I not too fussed
about that yet. I want to get some sort of directivity first. And
yes, I will try and interpolate and see if that helps.
Interpolation after the acquisition won't yield that much. Since it
seems you are bent on using a small uC you could try this:

a. Fire -> Acquire at 200ksps.
b. Fire one MCLK cycle delayed -> Acquire at 200ksps.
c. Fire two MCLK cycles delayed -> Acquire at 200ksps.
d. ...
.
.
.

Stop after you are one MCLK cycle away from a 360 turn on your 200kHz
ADC clock. Now stitch together all the information gathered. Now if your
uC begins to choke under all that data you could loosen the spec a bit,
maybe step several MCLK cycles each time but you need to get into the
vicinity of at least 1MSPS.

This is pretty much how digital scopes work in equivalent time sampling
mode, where their ADC isn't fast enough for the signal. It requires that
the signal doesn't move, or in your case that the targets don't move too
much.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Interesting, but wouldn't you have to capture 360*4=1440 signals? say
1000 samples per signal, that's a lot of data. It would guarantee
accuracy though. Also, I think my microcontroller only has one ADC
clock source, so I wouldnt be able to independently start different
channels. (will check though) All are linked to the same 200kHz
clock. Also, I dont think I can individually sample inputs manually
since the SAR ADC needs a sampling time.


If your targets don't move much you could process in chunks. For example, only take the first 100 samples, do all the clock stagger runs, calculate the result, store that, then move on to sample 101 through 200, and so on. It'll slow down the whole process but what can you do with such limited resources? Also you'd have to somewhat gracefully stitch together at the range ends, maybe let them overlap a few samples.

WRT the clock source I didn't mean switching the ADC clock but scooting the transmit pulses themselves. There you should have a much more direct control. For example you could run a timer and update the CCR after every shot. Of course, us HW guys always seem to run out of timers no matter how many there are on the uC ;-)


Good idea nevertheless...

I dont know about the interpolation, since the received signals are
pretty much sine waves, I'm quite confident that some sort of spline
or even polynomial interpolation will do pretty well with the signal.
The only problem that I can foresee is that my signals are not
synchronised. At the moment I can only sample 1 channel at a time due
to the rubbish on board ADC, but I have just got a new one where you
can sample synchronously, so hopefully after Ive rewritten the code
for that (argh) it should be ok.


Be careful. Multiple channels often come with speed penalties, IOW four channels can slash your sample rate to 1/4th.


I'm bent on using microcontrollers to capture the data because they
are cheap and quite easy to use. And I have quite a bit of experience
with them. What would you suggest I use? Thinking low cost?


Probably some kind of DSP would be better but it'll cost north of $5 in quantities. ARM might be another option since they often offer a lot more horsepower and RAM.

ADCs on uC are notoriously noisy so I'd consider an off-chip converter if the BOM budget allows it.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
.

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