measuring distance between two cars using infrared circuits

Guest
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .
 
In article <8f8Id.912$gX.230449@phobos.telenet-ops.be>, peter273
@hotmail.com says...
"Andrew Holme" <ajholme@hotmail.com> wrote in message
news:1106310278.349514.124760@z14g2000cwz.googlegroups.com...

gaurav.patil@gmail.com wrote:
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .

It might be easier with microwaves than infra-red:

Measure relative velocity using the Doppler effect. By integrating
this, you get a running estimate of the change in distance. Weird
things might happen when you go around corners!

Unfortunately, absolute measurement of short distances using
electromagnetic waves is difficult / impossible due to the speed of
light.
Click to expand...
The SoL is a nanosecond per foot. A nanosecond isn't a particularly
difficult thing to measure. Gate delays of modern semiconductor
processes are in the few picosecond range.

microwave is indeed more reliable
using a bursting microwave gives an indication of absolute distance and
speed between objects

timing between start of burst and start of reception of it is a measure for
absolute distance
doppler frequency gives relative speed
Click to expand...
No need for doppler measurements. Differentiate the distance
calculations.

--
Keith
 
<gaurav.patil@gmail.com> schreef in bericht
news:34583cf5.0501210131.4e999913@posting.google.com...
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .
Click to expand...
Mercedes-Benz uses a radar device in their adaptive cruise control system on
their S class cars. I think it's not easy to build such device yourself from
scratch.

Jeroen
 
gaurav.patil@gmail.com wrote:
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .
Click to expand...
One interesting, and perhaps simpler approach, is to take the same
approach that the sharp IR distance measurement devices use.

These are cheap ($10) electronics gizmos that take 5V, and output an
analog voltage that corresponds to the distance. They are not well
suited to your application, because their maximum range is something
like 80cm, but the scheme they use may be adaptable.

What they do is have an infrared LED, and a sensing device, which
consists of an array of sensors. The LED and the sensors are separated
by a fixed distance (maybe 3cm?), and arranged so that the returning IR
falls onto a particular sensor according to the angle. Using this, they
can sense the angle of return of the IR, and compute distance from that.

Seems like a similar scheme, albeit at a larger scale, might be usable.

Oddly enough, this is the scheme that bees' 'compound eyes' use. They
don't have a 'continuous' set of receptors like we do focused by a lens.
They sense changes with a set of cone shaped segments.

Feynman goes into detail about the compound eye in "The Feynman Lectures
on Physics", volume I, ch 36. He makes some typically clever
calculations, and determines that given a bee's eye, the maximal
resolution vs the diffraction of light at the wavelength they care about
will predict the shape of these cones. The formula he comes up with is

sigma = sqrt(lambda * r)

where sigma is the diameter of a segment at the tip, r is the length of
the segment, and lambda is the wavelength of light to be seen.

This may actually affect the minimum resolution of your detector. Say
your detector is w from the source, and you are projecting IR which has
a wavelength of lambda. You presumably wish to detect differences at
distances of about 10m. Say the resolution is deltaD. Then

deltaD = 0.5*w * (tan(t1) - tan(t2))

where t1 is the angle at the farther distance, and t2 is the angle at
the closer distance. Then by a little trig, we have

deltaD = 0.5*w*(1 + tan(t1)*tan(t2)) * (tan (t1-t2))

since by Feynman's formula,

sigma = sqrt(lambda * r)

if the angle of the opening is (t1 - t2), and the internal length is r,
we have

sigma = r * tan(t1 - t2)

so

r^2 * tan(t1-t2)^2 = lambda * r

and

tan(t1-t2) = sqrt(lambda/r)

thus, by the formula above,

deltaD = 0.5*w*(1 + tan(t1)*tan(t2)) * sqrt(lambda/r)

Now, assuming that w is 2m, and we want to detect differences at 10m,
tan(t1) is about 10. Thus

deltaD = 101 * sqrt(lambda/r)

For lambda = 1um, and a detector of 2cm in length, that means the
minimum distance resolution that can be detected is

deltaD = 101 * sqrt(1e-6/20e-3) = 750mm

before diffraction causes problems. This is 7% of the total distance!
However, if you use ultraviolet, then you can make the opening much
smaller, since the wavelength is smaller. For UV at lambda = 10e-7, you
can detect

deltaD = 101 * sqrt(10e-7/20e-3) = 255mm

which is a bit better.

At smaller angles, the (1 + tan(t)^2) factor gets smaller. Thus, at 5m,
we have 180mm, and at 2m, we have 35mm for IR with a 2cm r.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
 
On 21 Jan 2005 04:24:38 -0800, "Andrew Holme" <ajholme@hotmail.com>
wrote:

Unfortunately, absolute measurement of short distances using
electromagnetic waves is difficult / impossible due to the speed of
light.
Click to expand...
Well, radar was invented around 1939.

John
 
On Fri, 21 Jan 2005 13:17:12 -0800, John Larkin
<jjlarkin@highSNIPlandTHIStechPLEASEnology.com> wrote:

On 21 Jan 2005 04:24:38 -0800, "Andrew Holme" <ajholme@hotmail.com
wrote:


Unfortunately, absolute measurement of short distances using
electromagnetic waves is difficult / impossible due to the speed of
light.

Well, radar was invented around 1939.
Click to expand...
---
Yes, but back then everything was farther away.

--
John Fields
 
On Fri, 21 Jan 2005 01:31:11 -0800, gaurav.patil wrote:

hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .
Click to expand...
People have mentioned triangulation. Does a license plate retroreflect
laser pointer light?

Thanks,
Rich
 
On Fri, 21 Jan 2005 12:41:48 -0500, Mark Jones wrote:

Or use something much slower than light - ultrasonics.
Click to expand...
Why? If better than a few inch resolution is needed, which doesn't seem
to be the case here, use interferometry or as another poster said,
stereoscopic vision. The guts of a few optical mice may do a decent
stereoscope.

I'd think ultrasonics would be dicy in a noisy environment.

--
Keith
 
On Sat, 22 Jan 2005 23:41:45 -0500, keith wrote:

On Sat, 22 Jan 2005 07:32:19 +0000, Mac wrote:

On Fri, 21 Jan 2005 04:24:38 -0800, Andrew Holme wrote:


gaurav.patil@gmail.com wrote:
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .

It might be easier with microwaves than infra-red:

Measure relative velocity using the Doppler effect. By integrating
this, you get a running estimate of the change in distance. Weird
things might happen when you go around corners!

Unfortunately, absolute measurement of short distances using
electromagnetic waves is difficult / impossible due to the speed of
light.

It is not difficult at all. It just requires bandwidth. Before anybody
jumps on my case about detecting short CW pulses, let me point out that
short CW pulses have a LOT of bandwidth, and the shorter they are the more
bandwidth they have.

Ok, what's the bandwidth of a kHz modulated ~2GHz carrier (wherever there
is some free bandwidth). It should be trivial to measure the round-trip
delay to withing a nS, which is about six inches. At a kHz,
that gives us a distance measuremnt every millisecond, which should be
enough for distance and differentiate to give a relative velocity
number.
Click to expand...
Are you talking about on/off modulation of a 2GHz carrier at a 1KHz
rate? How long is the "on" time?

The same rules would apply to a modulated IR signal. There is no way the
OP is going to get any kind of high resolution ranging using IR alone
because there is just not enough bandwidth. (Some laser diodes have more
than enough bandwidth to do this, but I don't think they put out enough
power)

Since it *is* done, I'm not sure why you contend that it can't.
Click to expand...
Please elaborate. What is done? Are you saying that there is an IR diode
based system that can give precise range information? I am very interested
in this system.

Ultrasound might work well. You could have a transponder on the back of
the car in front and a range-finder on the front of the car in back.

It's *is* done without any transponder, which would make the idea useless.
Click to expand...
I admit that the transponder is not essential. It just makes it easier to
detect the signal, and increases the range over which the system would
work.

--Mac
 
"keith" <krw@att.bizzzz> wrote in message
news:pan.2005.01.23.19.07.53.59216@att.bizzzz...
On Sun, 23 Jan 2005 17:51:45 +0000, Mac wrote:

I admit that the transponder is not essential. It just makes it
easier
to detect the signal, and increases the range over which the system
would work.

It also adds an unknown and significant delay into the path.
Click to expand...
I disagree. In the grand scheme of a signal that's usually taking tens
of mS to make its journey, a few uS of turnaround overhead is not, IMO,
significant nor does it have to be an unknown.
 
"keith" <krw@att.bizzzz> wrote in message
news:pan.2005.01.23.04.41.43.607854@att.bizzzz...
On Sat, 22 Jan 2005 07:32:19 +0000, Mac wrote:

Ultrasound might work well. You could have a transponder on the back
of
the car in front and a range-finder on the front of the car in back.

It's *is* done without any transponder, which would make the idea
useless.
Click to expand...

It's not a useless idea, theoretically it could be put to fairly
practical use provided the obvious problems of using sound to
communicate on the freeway. Provided that you could transmit/receive a
signal approx 500' I could envision a system whereby:

1) the car in front could know fairly accurately how far the car behind
it was
2) it could also know how fast the car is going (i.e. how fast it is
encroaching)

If the front transponder was appropriately calibrated to a specific
frequency, the rear transponder of the leading car could use the
frequency of a received signal (and it's own speed) to calculate the
speed of the vehicle in behind it.

To calculate the distance, the onboard GPS's (all new vehicles will
eventually have one) 1 second pulsed output can be used to determine
when pings should be sent from the front transponder. By analyzing the
time shift of the start of the received signal, the rear transponder of
the leading vehicle can determine the distance to following vehicle up
to about 500'. A single bit of data could be embedded into the signal
to indicate that it was transmitted on odd vs. even numbered second to
extend range to about 1000'.

To distinguish transmitted return signals from reflections, a different
frequency is used. Standard compensation techniques for atmospheric
variations would be applied of course.
 
In article <pan.2005.01.22.09.23.03.387634@example.net>,
Rich Grise <richgrise@example.net> wrote:
[...]
People have mentioned triangulation. Does a license plate retroreflect
laser pointer light?
Click to expand...
Why not just image the plate with a camera and measure the image size with
software? When the cars get further apart the image of the plate gets
smaller. No LEDs needed.

--
--
kensmith@rahul.net forging knowledge
 
On Sun, 23 Jan 2005 20:19:03 +0000, Anthony Fremont wrote:

"keith" <krw@att.bizzzz> wrote in message
news:pan.2005.01.23.19.07.53.59216@att.bizzzz...
On Sun, 23 Jan 2005 17:51:45 +0000, Mac wrote:

I admit that the transponder is not essential. It just makes it
easier
to detect the signal, and increases the range over which the system
would work.

It also adds an unknown and significant delay into the path.

I disagree. In the grand scheme of a signal that's usually taking tens
of mS to make its journey, a few uS of turnaround overhead is not, IMO,
significant nor does it have to be an unknown.
Click to expand...
We're talking abotu cars a few tens of feet apart. Thus it's nanoseconds,
and *any* turn-around in the transponder is *significant*.

--
Keith
 
Doppler or direct time of flight, is doing it the hard way.

Chirp the transmitter at some number of MHz/uS
The reflection, even at a few nS delay, will be your carrier frequency of
that number of nS ago (can't be anything else!) so, the mix frequency
product at the receiver, will be proportional the the distance.

Smooth the output a bit to eliminate jitter, and you're there.
 
For a change of 1 foot at 50', that would be an angular change of
1/2500. It's better at 10', where a foot change would cause 1/100 change
in angle. If the maximum width were 500 pixels, then you could detect a
foot change (ie, 1/500 = 1 pixel) at 22 feet.
Click to expand...
Well, the good news is that as it becomes more important, it becomes easier
to see the difference.
:)
 
<gaurav.patil@gmail.com> wrote in message
news:34583cf5.0501210131.4e999913@posting.google.com...
hello,
i want to construct a circuit which will be able to measure distance
between two moving cars.The two cars are needed to maintain a fixed
distance between each other.
if the distance between them increases or decreases the circuit
should be able to detect this change and notify the amount of change
in the distance to both cars.
i want to construct this circuit using infrared LEDS ,so if any one
can help me out with this(circuit idea) please mail it to me .
Click to expand...

anyone ever thought of a "visual measurement" and using a moire-effect ?

Say the leading cars has a pattern of concentric circles or parallel lines,
and the trailing cars' visual system looks to first through also the same
kind of pattern, then a moire pattern will be seen
(same principle as looking through curtains, or on a computer monitor if
pixelsize gets close to dot-pitch)

interpretation of the moire is related to the effective distance

if defining the system well, the moire may even be a "growing shape" related
to the actual distance
 
React faster, probably. React better? No way. Unless this idea is
*very* well engineered, it will likely backfire with catastrophic
results.
Click to expand...
True, this is why it's only now becoming available, with work being done in
this direction since about the mid 80-s IIRC.
 
On Tue, 25 Jan 2005 14:39:36 -0500, Dave VanHorn wrote:

React faster, probably. React better? No way. Unless this idea is *very*
well engineered, it will likely backfire with catastrophic results.

True, this is why it's only now becoming available, with work being done
in this direction since about the mid 80-s IIRC.
Click to expand...
How do those supermarket door openers work?
(not the footpad - the ones with the little box over the door)

Thanks,
Rich
 
How do those supermarket door openers work?
(not the footpad - the ones with the little box over the door)
Click to expand...
Same thing, doppler microwave.
There may be some PIR units out there, but most are X or K band microwave.
 
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