Phased array sonar

Video of me sitting at 1.1m -17deg (or so) , moving my hand at 0.8m towards the center at 0.6m -2deg and back.

Video is processed with image enhancement and stacking algorithm, to reduce noise. I will add more videos in the future.

Link: Signal processing

Picture of my sampling gear

or maybe it was just a test of the Hackaday mobile app...

I received 4x hydrophones for an upcoming experiment. I plan on aligning them with element spacing of around 15cm, bring the frequency down to 1-5kHz. It wont have a transmitter making it listening device only. 

Hydrophones are going to be used with experiments of detection where underwater sounds are coming from. 

Beam pattern would look like

Frequencies below 5kHz and above 2kHz would give a reasonable direction ability. Whale songs is in this range.

So when weather gets better, I will take my EVO8 (channel sampler), my laptop, on a field trip to the local harbour.  

Experiments with the new 24ch 1cm element spacing array is too narrow or too wide.

Since it cant be any narrower, because mics' are 1cm wide, I am thinking about going back to 2cm spacing, extending the 16ch array to 24ch.

Why?

Beam radiation pattern for 1cm spacing, puts transmitter pulse frequency around 20kHz. 20kHz is nice, because you cant hear it, or.. at least I can't. (anymore).

But my crappy speaker have a hard time dealing with the max frequency spec'ed (or maybe its my cheap-o-film gaming amp that is garbage. Frequency response is dropping off a cliff fast around 20kHz, so transmitted pulse energy is really weak.

So, either I will go back to my 2cm array, where frequencies lie around 8kHz-14kHz, which is audible (nice for debugging, but annoying in the long run. Maybe I will also have problems with the CW pulse length being too short. 

Or, I buy new amp, speakers.

Or,  go for 40kHz range and use the cheap ultrasonic receivers and transmitters from SR04, which will require some clever arrangement of the receiver elements (and width is 1.6cm) since element spacing need to be 0.5cm.

For now, I will keep the current, and soon I will go back to 2cm element spacing.

Assembly and sound testing my 24 channel array. 

Element spacing has been changed to 1.01cm, which allows me to use pulse frequencies 18kHz-22kHz. This should give better range resolution, narrower beams, if my speakers can handle the frequencies.

Going ultrasonic, around 40kHz, would require me to reduce element spacing. With the current microphones, thats not possible. 

First test:

Anything above 2m, are reflections i.e. multi-path. To the right, at around 1m, there is a chair and a wall. There is a lot of "tuning" ahead. Image seems a bit noisy. Some of the noise are coming from side lopes, some are multi path.

Added beam radiation patterns

I added schematics for the PCB and PCB layout plus some pictures