Loop detector detector?

On Sun, 17 Aug 2014 12:52:43 -0400, Frank Krygowski
wrote:

On 8/17/2014 11:35 AM, Darrin Doc O'Leary wrote:
For your reference, records indicate that
Frank Krygowski wrote:

Before I do
a lot of trial and error, has anyone else solved this problem in a
do-it-yourself manner?

I solve the problem of faulty signals by disregarding them and going
through the intersection at the first safe opportunity.

Regarding Lou's "What is the problem" and Darrin's solution just above:
I have, of course, proceeded when safe at such intersections. But
usually "when safe" is a longer wait than successfully triggering the light.

There's one intersection at a busy highway very near a local school near
me, and kids can be dangerously impatient. A few miles further away, a
park road crosses another busy intersection. In both places, lots of
cyclists use the intersection, but detection is very unreliable.
However, it's fine if the bike is in precisely the right spot.

Marking the sweet spot would save time for cyclists, and help a
hazardous situation.

I assume that these lights are in your local village. Is it not
possible the get the local highway department to paint a location
marker on the pavement to indicate where a bicycle would have to be to
trigger the light?

--
Cheers,

John B.

On 8/17/2014 8:12 PM, John B. Slocomb wrote:

I assume that these lights are in your local village. Is it not
possible the get the local highway department to paint a location
marker on the pavement to indicate where a bicycle would have to be to
trigger the light?

There are a couple sets of lights (the ones near the school) that are in
my village. There are others that are in a neighboring township. And
there are probably many more in our metro area.

In my village, I've volunteered to do the painting myself. I can cut
the stencil. I've discussed this with the village council president
before, and will discuss it again.

But in general, someone needs to know where the sweet spot is, before
that spot can be marked. In some cases, I do know. In other cases, I
think nobody knows. Hence the desirability of a detector.

Incidentally, I'm considering whether it would be a good project for our
bike club to just bypass the red tape and do the marking ourselves.
That strategy has advantages and disadvantages, of course.

--
- Frank Krygowski

https://www.google.com/search?site=i...=isch&imgdii=_

On 17/08/14 17:22, Jeff Liebermann wrote:
On Sat, 16 Aug 2014 22:13:12 -0400, Frank Krygowski
wrote:

Any clues on detecting the position of a detector loop - IOW, the
location of the buried wire loops that are used to sense the presence of
a vehicle at a demand-actuated traffic light?

Most of the time, the pavement cuts (re-sealed with epoxy or something
similar) are visible, but on a couple of popular bike routes near here,
they've been paved over. That makes the lights difficult to trigger
when on a bike.

The loops are usually buried 2" below the pavement surface. If they
were buried an additional 2" the sensitivity would be reduced by a
factor of 4. The epoxy, tar, or whatever is used to seal the slot is
a fairly good insulator, which should not affect the loop
characteristics. However, asphalt and rocks are a fairly good
attenuator at low frequencies and will cause problems. I thought that
when resurfacing the roadway, the loops are suppose to be replaced so
as not to bury them.

I've been told the typical frequencies involved are 10-40 KHz.

Officially, 20 to 180 KHz. However, most of them land at about 40
KHz.

I've
been told some AM radios used to squeal when close to the loop.

Possibly a harmonic of the oscillator frequency. One would need to be
fairly lucky to tune the receiver to the exact frequency and have a
dirty enough 40KHz oscillator to hear the 25th harmonic. Bad idea.

Might it be interfering with an IF in the radio?

--
JS

Frank Krygowski writes:

On 8/17/2014 8:12 PM, John B. Slocomb wrote:

I assume that these lights are in your local village. Is it not
possible the get the local highway department to paint a location
marker on the pavement to indicate where a bicycle would have to be to
trigger the light?

There are a couple sets of lights (the ones near the school) that are
in my village. There are others that are in a neighboring township.
And there are probably many more in our metro area.

In my village, I've volunteered to do the painting myself. I can cut
the stencil. I've discussed this with the village council president
before, and will discuss it again.

But in general, someone needs to know where the sweet spot is, before
that spot can be marked. In some cases, I do know. In other cases, I
think nobody knows. Hence the desirability of a detector.

Incidentally, I'm considering whether it would be a good project for
our bike club to just bypass the red tape and do the marking
ourselves. That strategy has advantages and disadvantages, of course.

Because these are known locations, and you have a bit of time, the
simplest approach might be to use trial and error with a given bicycle
wheel and a bisection strategy using tape to mark previous spots.
As James opined, these sensors really need indicators.


--
Joe Riel

On Mon, 18 Aug 2014 13:40:33 +1000, James
wrote:

I've
been told some AM radios used to squeal when close to the loop.

Possibly a harmonic of the oscillator frequency. One would need to be
fairly lucky to tune the receiver to the exact frequency and have a
dirty enough 40KHz oscillator to hear the 25th harmonic. Bad idea.

Might it be interfering with an IF in the radio?

Nope. Going from 40 KHz to the common 455 KHz IF frequency, it's
still roughly the 11th harmonic. The common AM/FM car radio is fairly
well shielded from below by the floor board, and probably at least
-40dB down (my guess) from 455 IF feedthrough via the antenna. If
it's a more modernish all digital AM radio, there's no IF at all. The
AM broadcast signal is digitized and both filtered and demodulated
directly with a DSP (digital signal processor):
http://www.silabs.com/products/audio/fm-am-receiver/Pages/default.aspx
In other words, if you hear something on your AM radio, it's probably
not 455 Khz IF pickup.

However, if you are hearing strange noises over the loops on an AM
radio, my guess(tm) is that whatever is generating the 40 KHz loop
frequency, probably has a microprocessor or PIC controller buried
somewhere in the equipment cabinet. It might be radiating the clock
oscillator garbage out via the loop as an antenna. You can hear some
of that with any AM radio next to a street light controller box.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 17 Aug 2014 22:47:23 -0400, Frank Krygowski
wrote:

But in general, someone needs to know where the sweet spot is, before
that spot can be marked. In some cases, I do know. In other cases, I
think nobody knows. Hence the desirability of a detector.

It occurred to me that someone else might have a similar problem and
designed something for the purpose. Bingo:
http://www.atsi-tester.com/index.php/products/loop-and-detector-testers/loop-finder
One catch... It's $400.
https://shop.buckeyecam.com/store/home.php?cat=266

My guess(tm) is that they're using a commodity "EMF meter" as found on
eBay for about $15, to which they've added a 200 KHz low pass filter
to keep the broadcast transmitter interference out of the meter. It's
cheap enough for me to buy one and butcher, err... modify accordingly.
I'll let you know what happens in about 2 weeks (when I hopefully will
have some time to play).

Incidentally, I'm considering whether it would be a good project for our
bike club to just bypass the red tape and do the marking ourselves.
That strategy has advantages and disadvantages, of course.

Be sure to do a sloppy job of painting, so that the authorities can
claim that your bike club is completely incompetent at painting the
roadway. They'll take over and show the club how it's suppose to be
done. See the story of Tom Sawyer whitewashing a fence for details on
how it works.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 18 Aug 2014 00:17:23 -0700, Jeff Liebermann
wrote:

My guess(tm) is that they're using a commodity "EMF meter" as found on
eBay for about $15, to which they've added a 200 KHz low pass filter
to keep the broadcast transmitter interference out of the meter.

Here's a photo of the guts of two of the better "EMF meters".
http://eprs.blueherondatatechnologies.com/images/articles/detector_comparison.jpg
Note the large coil in the middle of the one on the left. That's what
makes it work, and what picks up the RF junk. The rest is just
amplification and display.

The meter on the right is a bit mysterious. I don't see a pickup
coil, which suggests that it uses a PCB (printed circuit board) trace
on the back to form some kind of pickup coil. Probably not very
sensisitve at lower frequencies and probably won't work at 40 KHz.

I just ordered something on eBay for $11. This should be interesting.
http://www.ebay.com/itm/231256078811
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 18/08/14 17:04, Jeff Liebermann wrote:
On Mon, 18 Aug 2014 13:40:33 +1000, James
wrote:

I've
been told some AM radios used to squeal when close to the loop.

Possibly a harmonic of the oscillator frequency. One would need to be
fairly lucky to tune the receiver to the exact frequency and have a
dirty enough 40KHz oscillator to hear the 25th harmonic. Bad idea.

Might it be interfering with an IF in the radio?

Nope. Going from 40 KHz to the common 455 KHz IF frequency, it's
still roughly the 11th harmonic. The common AM/FM car radio is fairly
well shielded from below by the floor board, and probably at least
-40dB down (my guess) from 455 IF feedthrough via the antenna. If
it's a more modernish all digital AM radio, there's no IF at all. The
AM broadcast signal is digitized and both filtered and demodulated
directly with a DSP (digital signal processor):
http://www.silabs.com/products/audio/fm-am-receiver/Pages/default.aspx
In other words, if you hear something on your AM radio, it's probably
not 455 Khz IF pickup.

Frank didn't mention it was a car radio.


However, if you are hearing strange noises over the loops on an AM
radio, my guess(tm) is that whatever is generating the 40 KHz loop
frequency, probably has a microprocessor or PIC controller buried
somewhere in the equipment cabinet. It might be radiating the clock
oscillator garbage out via the loop as an antenna. You can hear some
of that with any AM radio next to a street light controller box.


It might also be a 40kHz square wave (or heavily distorted 40kHz wave of
some description), with harmonics that spread way up through the spectrum.

--
JS

On Sat, 16 Aug 2014 22:13:12 -0400, Frank Krygowski
wrote:

No, that's not a typo.

Any clues on detecting the position of a detector loop - IOW, the
location of the buried wire loops that are used to sense the presence of
a vehicle at a demand-actuated traffic light?

Most of the time, the pavement cuts (re-sealed with epoxy or something
similar) are visible, but on a couple of popular bike routes near here,
they've been paved over. That makes the lights difficult to trigger
when on a bike.

I've been told the typical frequencies involved are 10-40 KHz. I've
been told some AM radios used to squeal when close to the loop. I've
also been told that it may be possible to detect it by using a suitable
coil of wire attached to a voltmeter, or perhaps an LED or two.

But none of the above is certain, and I'm an ME, not an EE. Before I do
a lot of trial and error, has anyone else solved this problem in a
do-it-yourself manner?


Have a look at http://www.google.com/patents/US7907065

which has a good explanation in the description of related art.