| Electronics > Beginners |
| Making a sound camera |
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| daslolo:
--- Quote from: MasterT on May 01, 2018, 11:40:13 pm --- --- Quote from: daslolo on May 01, 2018, 11:03:03 pm ---Yes that one. They all use logarithmic spiral. Anyone knows why? @MasterT good thing the complexity reinforce my decision of going all analog. By the way, speaking of ADC, are there ADC out there that do mass conversion all at once? Then I wouldn't have to spend time in the mCU and counter-offset the signals. Anyway I got the FFT running, and having two cores is sweet, so I might as well use programming to make this thing. --- End quote --- Logarithmic spiral is to impress potential customer, that sound camera is indeed very complex and consequently costly feature. Btw, I should say that I did a sound localizer/ camera twice in the recent past, one with arduino Leonardo and arduino DUE. You don't have to spend 120 usec or so to wait an adc conversion complete. There are two ways to save time. On the 8-bits atmega controllers you activate adc conv. complete interrupt, and go into interrupt subroutine when sample is ready. It's about 6-10 usec, compare to 120 usec if in waiting state. I'm talking atmega328/atmega32u4 etc. Arduino DUE has DMA, so you go into interrupt subfunction only once when complete data array is ready, and sampling 1 msps is quite easy to do w/o CPU involvement. Nice you have fft running, now you should check the timing, if you can run fft on stream of data (4 mics - 10k *4 = 40 ksps or so). There are some optimization may be required. Arduino DUE for example iis capable to process data via fft with 250-300 ksps, and optimization is not requred even to HI-FI 48kHz *4 =< 200 ksps sound. But I did optimize a processing on arduino Leonardo, interleaving processing for left /right than top/ bottom mics, as Leonardo is good for about 20 ksps. --- End quote --- The Spiral does look scienty and the housing looks desirably expensive. I'd love to see your sound camera in action, do you have a link of your project? I didn't know the arduino boards could push 1msps! is this per channel? Through the arduino dev IDE or are you poking at registers directly? I don't know how to calculate sps but maybe you're talking about the sampling frequency. In that case I'm sampling at 10khz. As for the FFT timing, on the esp32, one 512 bin FFT takes 14ms, the capture takes 10ms @ 10khz, 40Khz is the sampling limit using a delayed loop of analogRead. Someone bypassed the register safety lock and managed 25 MHZ output so fast input sampling must be possible but I must say I didn't understand it yet how it's done and what the impact on using a second core for capturing (what I'm doing) is. I haven't used DMA but I read that the esp32 has DMA as well, I don't know if this is the same access as your DUE though. |
| hamster_nz:
The spiral looks like the one used as the core of the Square Kilometer Array. https://www.skatelescope.org/layout/ --- Quote ---The spiral layout design has been chosen after detailed study by scientists into how best optimise the configuration to get the best possible results. This spiral configuration gives many different lengths (baselines) and angles between antennas resulting in very high-resolution imaging capability. The perfect layout would be a random arrangement that maximises the number of different baselines and angles between antennas. However, the practicalities of construction as well as linking the antennas together with cables mean that the spiral configuration is the best trade off between image resolution and cost. --- End quote --- |
| mikeselectricstuff:
Someone posted here a while ago that they had done something similar They used digital-output MEMS microphone modules and an FPGA, to make a pretty cheap system I don't recall how far they got in producing visual output. |
| mikeselectricstuff:
I think this was it https://hackaday.com/2016/07/01/1024-pixel-sound-camera-treats-eyes-to-real-time-audio/ |
| mikeselectricstuff:
--- Quote from: daslolo on May 01, 2018, 11:03:03 pm ---Yes that one. They all use logarithmic spiral. Anyone knows why? --- End quote --- My guess would be something to do with standing waves and/or having a large number of different mic-to-mic distances while maintaining symmetry of sensitivity Digital-output MEMS mics with I2S or pulse-modulation schemes are very cheap, so it may make sense to trade off number of mics versus processing complexity |
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