DPRG mailing list archives: [DPRG] Cool Christmas Presents

Wed Dec 27 21:05:25 CST 2006

Ed P.,

Found that site about 30 seconds after my e-mail was sent. :)

0-100Hz sounds about right for Doppler shift.  Hook it to an audio amp and
walk across the room in front of it, the tone should change with your
speed.

Now I wonder how to convert them to Time-Of-Flight?  The Doppler might be
useful as an alternate way of getting ground speed from a large outdoor
robot, or measuring the speed of quick trip robots, but not much else.  A
true TOF unit would be a really cool alternative to sonar and IR though,
with a much larger potential range.

Ed O.

> Ed O.,
>
> I just read the entire thread here:
> http://www.austech.info/showthread.php?t=135840&page=1
>
> They seem to be most concerned with using the measuring electronics
> with other more powerful TX/RX pairs to make homebrew radar guns, but
> the posts by "mitaux8030" and "Trash" are pretty informative.
>
> I just finished tearing the beast apart, etc.  First off: its a real
> beast to get apart.  You have to drill out the plastic plugs to get at
> the screws.  A big hint is to get the two end caps off first.
>
> I've got the waveguide/TX/RX/mixer unit on my bench.  The signal
> coming out of it doesn't seem to get any better by powering the unit
> continuously versus the 25% on, 8khz duty cycle the unit originally
> uses.
>
> I need to build an amp and fiddle with some filters to see if I can
> get an obviously measurable signal out of it.  I'm also need to find a
> book to figure out what sort of frequency range to expect out.
> 0-100Hz seems to appear, but I'm not sure if thats due to real doppler
> affect, or my hand affecting the near-field of the TX/RX pair.
>
> I've got pictures of the gun disassembled. They sort of fill the gaps
> of the pictures on that forum.  I'll get them up on a site soon.
>
> Ed P.
>
> On 12/27/06, Ed Okerson <ed at okerson.com> wrote:
>> Ed,
>>
>> What search terms did you use?  I have not been able to find any useful
>> info so far.
>>
>> Ed
>>
>> > Ed,
>> >
>> > When I got back to Austin today, I stopped by the local Walmart and
>> > picked up one of those hot wheels radar guns.  Pretty slick!  They
>> > appear to be on clearance for $20.00 and I saw them at HEB later for
>> > $12.50.
>> >
>> > I found some pictures online, and it seems that its using doppler
>> > shift, not time of flight.  Makes sense, because thats cheap.   There
>> > is some discussion on boosting the power, too.
>> >
>> > But it seems that the base signal is being measured and displayed by a
>> > microcontroller of some sort.
>> >
>> > So the question to everyone is this:
>> > Given a sensor that gives you the speed of a moving object, can you
>> > produce 'interesting' data for navigation?
>> >
>> > Perhaps use it while driving to check your odometry by measuring your
>> > own speed against the ground?
>> >
>> > Sweep it 360 degrees and create a sort of optical flow map?
>> >
>> > Use two at once and come up with the speed of two points in front of
>> > you, then compute a line (gradient) that could give you speed and
>> > direction of travel?
>> >
>> > I've not opened mine up yet, but from the pictures, the base-band
>> > processor would easily be replaced.
>> >
>> > Ed P
>> >
>> >
>> > On 12/26/06, Ed Okerson <ed at okerson.com> wrote:
>> >> So what cool toys did everyone find under the tree?
>> >>
>> >> My kids got me the Hot Wheels Radar Gun.  How they manage to make a
>> real
>> >> Doppler radar gun for $20 is beyond me.  Now to figure out a good
>> >> robotics
>> >> use for it.  I wonder how hard it would be to make a sonar
>> replacement?
>> >>
>> >> Anyone going to RBNO tonight?
>> >>
>> >> Ed
>> >>
>> >> _______________________________________________
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>> >> http://list.dprg.org/mailman/listinfo/dprglist
>> >>
>> >
>>
>>
>>
>