Reading driver displacement with radar!

[kenpeter]

Cheep sonar? Nothing comes to mind, cept maybe an old Polaroid camera.

[littlemike]

Originally Posted by davygrvy

Can you buy that as a $35 toy to dismantle? 2 years ago these Hot Wheels Radar Guns went for $9.99 at CircuitCity

Pity - they are closer to $100 now.

[davygrvy]

Probably cheaper at a local toy store that has some than from Amazon.com. Or there's garage door sensors, too, that use doppler. Or there's even building your own waveguide from an old coffee tin or whatever. The osc and mixer circuit, I have no clue on at the moment, but probably isn't that difficult to make except for the tuning tools needed, which probably don't come cheap.

[jbell]

a dumb thought floating through my head, what does the backemf from a sub look like once coil goes out of the gap, and past xmax? In the servocontrol from rhythmic, they use a separate sensing coil to control the servo... just wondering without that sensing coil if you can accomplish a similar feedback loop for your brown note without the sonar?

although, I have to admit, this is way geekier than making a 2.4ghz antenna out of a pringles can !!

btw, ever given any thought to v-coupling your AT's? (3 and 3, facing toward the point of the V. All you'd have to build is the part for them to fire into.... It'd get you closer to 30hz Fc)

[davygrvy]

Hi Jim. I'm not searching for the brown note, but I am sick. I had a headache all this afternoon from blasting 30Hz in my garage. I still have it. So I took the time to put in a mouser order and work-out on paper the control circuit for the gain reducer. I think I saw the same WiFi antenna article, too, with the pringles can.

I don't know if there is a way to calculate backemf from a coil that is being driven. An undriven coil acts as a pickup from the motion through the cap. If the drive voltage becomes rather different than the pickup coil...

Velodyne used a piezo element in their cones as an accelerometer to determine displacement. They were notorious for breaking. There's also laser interferometry but that's too exact and has a resolution down to 1/4 the wavelength of the laser which for red is 161nm. That's crazy small. Or there's bouncing a laser beam off of a reflecting surface like tin foil to an X detector. The six-pack already does 34Hz F3, 29Hz F10 in 1/2 space.

12kHz in sound has the same wavelength of 10.525 GHz of RF. Diagnostic ultrasound is around 2 MHz. So that'll need the more complex FtoV conversion.

I'm not looking for any other method, this seems to work as is without any fuss.

If I wanted to V-couple, I'd make some T-36 cabs to drop the HL10s into. Am I trying to go lower, no. What I'm trying to do is to use real world limits as limiter inputs. Not some inference from an excursion/power/frequency chart to set your assumed safe high-pass. The six-pack already does 34Hz F3, 29Hz F10 in 1/2 space.

[jbell]

Originally Posted by davygrvy

I think I saw the same WiFi antenna article, too, with the pringles can..

Well, we took that to a ridiculous extreme a few years ago. Seems a local telephone company was trenching rural fiber, and providing internet access/telephone. About 10 miles away was the closest it would get to my dad's farm. So, we set a wap11 on top of a windmill with a yagi, pointing line of site to a 100' silo. On top of that silo was yagi's with 3 wap11's back to back. One to the local school 18 miles away, one to my dad's farm close and one to my brother's place about 10 miles away. The receiving antenna at my brothers place is the one I think you'll be interested in... Seems there was an unused birdview aluminum C-band dish... and not wanting to spend money on yet another yagi... well a makeshift 2.4ghz waveguide on that dish worked incredibly well... Not sure the fcc would have been terribly happy with any of that --- but it worked well for about 2 years, till a better internet solution could be had. (often wondered what the gain on a 10' aluminum is....)

Your sonar effort reminds me of that. Using simple tools to do something cool. great idea, thanks for sharing.

[davygrvy]

Now that's kewl.

[davygrvy]

http://www.facebook.com/v/1234283770983

[littlemike]

Now that is SWEET.

[davygrvy]

Rough schematic of what I showed at BAF2009. Sorry for the delay for those who asked.

Replace R15 with a pot to adjust threshold. U3 is used as a compensator to adjust-out a 2nd harmonic distortion caused by inverse-square. As the driver comes closer to the antenna, the signal goes up, thus causing a "fat bottom" to the signal. U3 compensates by applying an adjustable square function. It probably isn't need, but my eyes told me I had to have it.

Active differential input and active servo floating output missing.. apply as required. Or transformers if you like