electrical compass idea...

Archiver

Interesting idea.
But it might be easier to use a Dinsmore device to do what you want as it
would save you a lot of hassles trying to get a small compass needle to
move.
The Dinsmore device comes closest to what your thinking about.
The Devantech digital compass is another nice device as well, but it does
work differently though.
You can buy the devices separately, or you could get the Parallax App Mod
that has it all in a module that's easy to use.

http://www.dinsmoresensors.com/

http://www.parallax.com/detail.asp?product_id=29113

http://www.acroname.com/robotics/parts/R117-COMPASS.html

---

Original Message

---

From: Hudson T Clark [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ETzP-Zkf890eveVPCkaaNpIXevfkddgWwqQWzhCo9SJ5a6t4IEC8Vusi_P6xPQDFlFNICbHuhcZZWeF8Ang]dark_archon1@j...[/url
Sent: Tuesday, June 17, 2003 4:00 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] electrical compass idea...


I just had an idea maybe someone can give me some feedback. I was just
thinking how I could make a nice CHEAP little electrical compass. Ok so a
compass a human uses has a needle on a little disc with the directions
(N, W, S, E) and you can tell by the position of the needle. Ok well lets
see, how does POT work kind of the same and a rheostat works like this
right? What if I come up with a modified compass that will have a broken
place in the disc somewhere so I could attach a lead to this, and then
attach a second lead to the thing the needle is spinning on. This would
create an electrical circuit, and then I would have to replace the
plate... with something that's like resistive, etc so the resistance
would vary depending on where the needle was. Then I can come up with a
reference (like how much resistance dead north is) and probably use like
a very high resolution (for more accuracy) A/D converter to figure out
the resistance in my basic stamp... I don't know exactly how I would do
this I may need to read about how electrical components are built (maybe
even some physics???). But I was just thinking this could be a way cool
project for a novice to work on! Anyone have some input?

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Archiver

Hudson:

It is probably doable, and certainly cheaper than buying a ready made
module. It might even be more fun, depending on how frustrating it can get.
One problem you would have to solve is mentioned in other posts, and that is
the problem of wiper noise, usually encountered in Pots. I do know that I
saw a pot once that was made out of a piece of PC board, etched in a circle,
with a cutout. Two leads were soldered to the ends of the circle, and a hole
was drilled into the middle, on which was mounted a windvane. Same general
idea as yours, except he just used an indoor replica of the windvane and the
electrical resistance from the slider to the ends of that arc to position
the inside vane, so that whatever way the outside vane pointed, the inside
one did, too. You could use the idea but would just have to provide a slider
that could be put on the central shaft, and moved easily over the copper
traces. Then if you applied the two ends of the trace to a Wheatstone Bridge
arrangement, with the slider being the junction between two resistances, you
would have a very sensitive differential circuit from which to derive
relative pointer position. If you use the absolute mid point of the arc as
your relative 12:00 bearing, or zero degrees relative, then you would be
able to resolve everything except 6:00 exactly, which would be your back
azimuth, but in exchange for the back azimuth, you would get up to about 358
degrees of other coverage. Add a second arc, concentric with the first, 180
degrees out from it, and physically connect two electrically isolated
sliders end to end, and you could even get 360 degrees, and both your zero
degree relative heading and your back azimuth for any direction. You problem
still would be how to get the sliders to turn easily enough to respond to
the earth's gravity field and still be able to provide enough pressure on
the slider contact area to get reliable, and non-noisy readings.

Mic

---

Original Message

---

From: Hudson T Clark <dark_archon1@j...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, June 17, 2003 4:59 AM
Subject: [noparse][[/noparse]basicstamps] electrical compass idea...


> I just had an idea maybe someone can give me some feedback. I was just
> thinking how I could make a nice CHEAP little electrical compass. Ok so a
> compass a human uses has a needle on a little disc with the directions
> (N, W, S, E) and you can tell by the position of the needle. Ok well lets
> see, how does POT work kind of the same and a rheostat works like this
> right? What if I come up with a modified compass that will have a broken
> place in the disc somewhere so I could attach a lead to this, and then
> attach a second lead to the thing the needle is spinning on. This would
> create an electrical circuit, and then I would have to replace the
> plate... with something that's like resistive, etc so the resistance
> would vary depending on where the needle was. Then I can come up with a
> reference (like how much resistance dead north is) and probably use like
> a very high resolution (for more accuracy) A/D converter to figure out
> the resistance in my basic stamp... I don't know exactly how I would do
> this I may need to read about how electrical components are built (maybe
> even some physics???). But I was just thinking this could be a way cool
> project for a novice to work on! Anyone have some input?
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

Archiver

Sounds neat, but I don't think it would be practical in execution.
The main problem would be keeping good contact between the wiper (compass
needle) and the resistive surface, while still keeping friction low enough
to permit the needle to swing freely. If you look at a real compass, you'll
notice that the needle is usually floating in liquid or balanced on the tip
of a pointy rod, to minimize friction.

As Earl said, go with the Dinsmore sensor! They're cheap, and work well.

- Robert

Archiver

Another idea, would be to use numerous lights, or mini LEDs around the
perimiter. When the needle passed in front of, or blocked a light, you could
have a photocell detect that differance and know where the needle was.
Resolution would be based on the number of lamps of course.
Just ideas for fun more than practicality.
-Kerry

At 08:37 PM 4/6/03 -0400, you wrote:
>Hudson:
>
>It is probably doable, and certainly cheaper than buying a ready made
>module. It might even be more fun, depending on how frustrating it can get.
>One problem you would have to solve is mentioned in other posts, and that is
>the problem of wiper noise, usually encountered in Pots. I do know that I
>saw a pot once that was made out of a piece of PC board, etched in a circle,
>with a cutout. Two leads were soldered to the ends of the circle, and a hole
>was drilled into the middle, on which was mounted a windvane. Same general
>idea as yours, except he just used an indoor replica of the windvane and the
>electrical resistance from the slider to the ends of that arc to position
>the inside vane, so that whatever way the outside vane pointed, the inside
>one did, too. You could use the idea but would just have to provide a slider
>that could be put on the central shaft, and moved easily over the copper
>traces. Then if you applied the two ends of the trace to a Wheatstone Bridge
>arrangement, with the slider being the junction between two resistances, you
>would have a very sensitive differential circuit from which to derive
>relative pointer position. If you use the absolute mid point of the arc as
>your relative 12:00 bearing, or zero degrees relative, then you would be
>able to resolve everything except 6:00 exactly, which would be your back
>azimuth, but in exchange for the back azimuth, you would get up to about 358
>degrees of other coverage. Add a second arc, concentric with the first, 180
>degrees out from it, and physically connect two electrically isolated
>sliders end to end, and you could even get 360 degrees, and both your zero
>degree relative heading and your back azimuth for any direction. You problem
>still would be how to get the sliders to turn easily enough to respond to
>the earth's gravity field and still be able to provide enough pressure on
>the slider contact area to get reliable, and non-noisy readings.
>
>Mic
>

---

Original Message

---

>From: Hudson T Clark <dark_archon1@j...>
>To: <basicstamps@yahoogroups.com>
>Sent: Tuesday, June 17, 2003 4:59 AM
>Subject: [noparse][[/noparse]basicstamps] electrical compass idea...
>
>
>> I just had an idea maybe someone can give me some feedback. I was just
>> thinking how I could make a nice CHEAP little electrical compass. Ok so a
>> compass a human uses has a needle on a little disc with the directions
>> (N, W, S, E) and you can tell by the position of the needle. Ok well lets
>> see, how does POT work kind of the same and a rheostat works like this
>> right? What if I come up with a modified compass that will have a broken
>> place in the disc somewhere so I could attach a lead to this, and then
>> attach a second lead to the thing the needle is spinning on. This would
>> create an electrical circuit, and then I would have to replace the
>> plate... with something that's like resistive, etc so the resistance
>> would vary depending on where the needle was. Then I can come up with a
>> reference (like how much resistance dead north is) and probably use like
>> a very high resolution (for more accuracy) A/D converter to figure out
>> the resistance in my basic stamp... I don't know exactly how I would do
>> this I may need to read about how electrical components are built (maybe
>> even some physics???). But I was just thinking this could be a way cool
>> project for a novice to work on! Anyone have some input?
>>
>> To UNSUBSCRIBE, just send mail to:
>> basicstamps-unsubscribe@yahoogroups.com
>> from the same email address that you subscribed. Text in the Subject and
>Body of the message will be ignored.
>>
>>
>> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>>
>>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
-Yours with much regard
-Kerry

Archiver

I haven't followed this thread in detail, I just ran across someone's
reply, so forgive me if someone else has said this already.

Before the advent of flux-gate compasses, I gather that some boat
autopilots used a magnetic compass of the moving card rather than the
moving needle variety. (Boat compasses are moving card, whereas "boy scout"
compasses tend to be moving needle).

The compass card had a series of markings (light and dark areas) - Gray
code - that were detected by a pair of photocells. When the card moved, the
photocells detected this anc could measure the angular distance moved.

You could modify a moving-card compass, and print your own Gray code on a
piece of paper and fasten it to the card.

However if you want to work with a moving needle compass, I don't know how
you could do it. I doubt that you could use a pot, since the force
developed by the needle is very small.

Have fun!




Larry Bradley
Orleans (Ottawa), Ontario, CANADA

Archiver

At 09:48 PM 6/17/03 -0700, you wrote:
> >Sounds neat, but I don't think it would be practical in execution.
> >The main problem would be keeping good contact between the wiper
>(compass
> >needle) and the resistive surface, while still keeping friction low
>enough
> >to permit the needle to swing freely. If you look at a real compass,
>you'll
> >notice that the needle is usually floating in liquid or balanced on the
>tip
> >of a pointy rod, to minimize friction.
>
> >As Earl said, go with the Dinsmore sensor! They're cheap, and work well.
>
> >- Robert
>
>The whole purpose is for me to come up with a way to modify a regular
>compass, but thank you.

The problem with a POT is going to be friction. Define "regular compass"
anyway...If you suspend a magnet from a string is that not a compass of the
regular variety? Anyway for "cheap" I would use two rare earth cobalt magnets
sandwiching a string, perhaps gluing a disk to the magnets that I can detect
the orientation optically, or simply use hall-effect transistors strategically
around the suspended magnets.

-Beau Schwabe

Archiver

Another thing would be a disc of paper with light and dark stripes. Just
like a wheel encoder that people use for their robot wheels to sense
distance. The Stamp could count the turns of the encoder, or the stripes
passing the sensor, rotation could be determined by the count this way. The
encoder disc could be printed on a printer, and a metal needle attached to
force the disc to rotate.
-Kerry

At 01:50 PM 6/18/03 -0700, you wrote:
>No no no I was merely saying its "like" a pot in such that its something
>turning like a disc... I was saying I could make something similiar like
>this but on a compass maybe. But this light idea is interesting. I was
>also reading about gyroscopes but that seems like it would be a very
>complicated thing to make electronic heh.
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
Very respectfully, your obedient servant.
Kerry
Admin@M...
WWW server hosting [url=Http://mntnweb.com]Http://mntnweb.com[/url]
Kerry Barlow
p.o. box 21
kirkwood ny
13795
607-775-1575

Archiver

Hmm. Maybe a perforated drum to replace the needle, with a magnet glued to
its bottom (bar magnet, for a more powerful response to magnetic fields than
the needle would give). Then the drum would always be oriented with the
"North" slot toward magnetic north. If you zeroed the bot's direction sensor
before moving (in reality, if you stored its last position count relative to
north at shutdown, you wouldn't have to zero it), and counted light
interuptions as turn increments (say, a slot every 5 degrees, and maybe
elongate every 6th one, at 30 degree intervals, stack two light sensors,
such that whenever the top one (30 degree) sees light, it checks the count
used by the bottom one (5 degrees), and rounds it to the nearest multiple of
6, you could always keep a relative bearing that was accurate to 5 +-5
degrees. And in truth, it probably would be pretty much 5, without the +-,
since 6 increments is a large enough chunk that the circuit wouldn't be
likely to correct in the wrong direction, even for a two slot error (if the
actual count is 12 slots, or 60 degrees, but the 5 degree counter is holding
10, or 50 degrees, a correction to 12 @ 60 degrees is more likely than a
back correction to 6 @ 30 degrees, since the correction up is only two
increments @ 10 degrees, and the correction down is 4 @ 20). You'd probably
still want to include a means of stopping now and then to line up a couple
of fixed lights and zero the compass card, or something. This is how the old
Inertial Navigation Systems, based on 50 to 100 pound gyroscopes worked, and
they had circular probability errors creep in, so they had to be zeroed to a
known reference every now and then.

But maybe the drum is a bad idea. How about a CD, with black tape strips on
it from center to rim every 5 degrees, but only half the distance on every
sixth one. Then shine two lamps or collimated LEDs up from below, and put
the light sensors right beside the source LEDs. Ready made interruptor,
cheap, and VERY low center of gravity. Now how do we stick the magnet to the
CD and still keep it in balance so it will turn easy? What kind of bearings
does a CD drive motor run on? Those seem to be incredibly smooth and
friction free, given the low mass and inertia of a CD, and how long it keeps
spinning after shutdown.

Mic

Yeah. Definitely forget my needle as a slider on a copper ring idea. This
sounds much better. And it has 360 degree coverage without overlapping
rings. Calculating back azimuth could get a little tough, though.

---

Original Message

---

From: Hudson T Clark <dark_archon1@j...>
To: <basicstamps@yahoogroups.com>
Cc: <basicstamps@yahoogroups.com>
Sent: Wednesday, June 18, 2003 12:47 AM
Subject: Re: [noparse][[/noparse]basicstamps] electrical compass idea...


> >Another idea, would be to use numerous lights, or mini LEDs around the
> >perimiter. When the needle passed in front of, or blocked a light, you
> could
> >have a photocell detect that differance and know where the needle was.
> >Resolution would be based on the number of lamps of course.
> >Just ideas for fun more than practicality.
> >-Kerry
>
> This is a grate idea... For sure some more thinking should be put into a
> design...
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

Archiver

Larry:

Nothing to forgive. I think we both got to the same place at almost the same
time, since moving card compasses are one of the family of Inertial
Navigation Systems I mentioned in another post about 10 minutes ago. Thanks
for jumping in. My tired brain needs all the help it can get.

Mic

---

Original Message

---

From: Larry Bradley <lhbradley@i...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, April 07, 2003 9:06 AM
Subject: Re: [noparse][[/noparse]basicstamps] electrical compass idea...


> I haven't followed this thread in detail, I just ran across someone's
> reply, so forgive me if someone else has said this already.
>
> Before the advent of flux-gate compasses, I gather that some boat
> autopilots used a magnetic compass of the moving card rather than the
> moving needle variety. (Boat compasses are moving card, whereas "boy
scout"
> compasses tend to be moving needle).
>
> The compass card had a series of markings (light and dark areas) - Gray
> code - that were detected by a pair of photocells. When the card moved,
the
> photocells detected this anc could measure the angular distance moved.
>
> You could modify a moving-card compass, and print your own Gray code on a
> piece of paper and fasten it to the card.
>
> However if you want to work with a moving needle compass, I don't know how
> you could do it. I doubt that you could use a pot, since the force
> developed by the needle is very small.
>
> Have fun!
>
>
>
>
> Larry Bradley
> Orleans (Ottawa), Ontario, CANADA
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

Archiver

Yep. Ring Laser Gyro. Terribly small, just a very tiny mirror to turn, and a
laser and sensors for positioning, and VERY VERY exotic and complex for what
we are trying to do. And mechanical gyros are very heavy (got to have lots
of inertia, for which read, spinning mass), and suffer from something called
precession error, which ..., well, never mind. I don't even think I can
explain it on a keyboard, but you can see its effects by spinning a tire on
an upended bicycle, and pushing up or down on one end of the axle with your
finger. It moves on an axis up to 90 degrees off the axis on which you are
pushing. Which sets up smaller forces up to 90 degrees away from that
induced force. Which repeats itself over and over again (Is this beginning
to sound like "big fleas have smaller fleas, upon their backs to bite 'em,
and smaller fleas have lesser fleas.... ?). Anyway, the cumulative forces
cause a gyro to try to fall over, and to slow down over time, and cause a
gyro compass card to have cumulative errors.

Mic

---

Original Message

---

From: Hudson T Clark <dark_archon1@j...>
To: <basicstamps@yahoogroups.com>
Cc: <basicstamps@yahoogroups.com>
Sent: Wednesday, June 18, 2003 4:50 PM
Subject: Re: [noparse][[/noparse]basicstamps] electrical compass idea...


> No no no I was merely saying its "like" a pot in such that its something
> turning like a disc... I was saying I could make something similiar like
> this but on a compass maybe. But this light idea is interesting. I was
> also reading about gyroscopes but that seems like it would be a very
> complicated thing to make electronic heh.
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

Archiver

I just had an idea maybe someone can give me some feedback. I was just
thinking how I could make a nice CHEAP little electrical compass. Ok so a
compass a human uses has a needle on a little disc with the directions
(N, W, S, E) and you can tell by the position of the needle. Ok well lets
see, how does POT work kind of the same and a rheostat works like this
right? What if I come up with a modified compass that will have a broken
place in the disc somewhere so I could attach a lead to this, and then
attach a second lead to the thing the needle is spinning on. This would
create an electrical circuit, and then I would have to replace the
plate... with something that's like resistive, etc so the resistance
would vary depending on where the needle was. Then I can come up with a
reference (like how much resistance dead north is) and probably use like
a very high resolution (for more accuracy) A/D converter to figure out
the resistance in my basic stamp... I don't know exactly how I would do
this I may need to read about how electrical components are built (maybe
even some physics???). But I was just thinking this could be a way cool
project for a novice to work on! Anyone have some input?

Archiver

>Another idea, would be to use numerous lights, or mini LEDs around the
>perimiter. When the needle passed in front of, or blocked a light, you
could
>have a photocell detect that differance and know where the needle was.
>Resolution would be based on the number of lamps of course.
>Just ideas for fun more than practicality.
>-Kerry

This is a grate idea... For sure some more thinking should be put into a
design...

Archiver

>Sounds neat, but I don't think it would be practical in execution.
>The main problem would be keeping good contact between the wiper
(compass
>needle) and the resistive surface, while still keeping friction low
enough
>to permit the needle to swing freely. If you look at a real compass,
you'll
>notice that the needle is usually floating in liquid or balanced on the
tip
>of a pointy rod, to minimize friction.

>As Earl said, go with the Dinsmore sensor! They're cheap, and work well.

>- Robert

The whole purpose is for me to come up with a way to modify a regular
compass, but thank you.

Archiver

No no no I was merely saying its "like" a pot in such that its something
turning like a disc... I was saying I could make something similiar like
this but on a compass maybe. But this light idea is interesting. I was
also reading about gyroscopes but that seems like it would be a very
complicated thing to make electronic heh.

Archiver

Oh but I so enjoy the replies, I like that you all are so talkative I
think I won't Smile you off like activestate tee hee hee.