Eagle ERC questions

[John Coppens]

On Wed, 30 Jul 2008 17:33:19 -0400 (EDT)
piclist@... wrote:

> What about ultrasonic triangulation?  Lets see, speed of sound is
> 1100ft/s so thats 13,000in/s so a tick rate of 13,000 per second gets
> you down to an inch of percision.  Three transmitters will do it, more
> if you have an odd area that can't be covered by just three.

It will need temperature sensor - sound speed changes quite a lot (about
1% each 5 degrees Centigrade). That's not too much - about 1 meter over
50 m for a 10 degree C change - but still... I'd also worry about
reflections against walls and other obstacles.

Also, take into account wind direction/speed. A 10 knot wind (18km/h) is
about 5 m/s error on the 330m/s sound speed, another 1.5%.

> Another idea is a beacon like an IR led on the robot, and cheap USB
> cameras looking down.  From the position of the LED in the camera's
> view you can easily calculate it's position.  A system to do just that
> us used to track foul balls in tennis.  Then you just need enough
> cameras to cover the area it will move about in, and a computer to
> calculate and transmit the position to your robot.

This might get complicated - USB cables only bridge 2m each... And,
ideally you'd have to put the cams _above_ the grass to be cut, else
resolution errors will cause large positional errors after perspective
correction (and I have seen distorsion of cheap camera lenses reach 10%).

I don't want this to sound as criticism... I'm as interested as the next
man to get my machine do its work solo ;-)   (it doesn't - yet)

I haven't studied those laser measuring devices I've seen advertised.
Maybe they have some digital output that could be used to maintain a
constant distance from a wall or so.

John
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[piclist-7]

On Wed, 30 Jul 2008, John Coppens wrote:
> This might get complicated - USB cables only bridge 2m each... And,
> ideally you'd have to put the cams _above_ the grass to be cut, else
> resolution errors will cause large positional errors after perspective
> correction (and I have seen distorsion of cheap camera lenses reach 10%).
>
> I don't want this to sound as criticism... I'm as interested as the next
> man to get my machine do its work solo ;-)   (it doesn't - yet)

I wouldn't post ideas if I didn't expect them to get poked with a stick. :)

I read some papers on optical tracking using cameras and one of the
techniques is to move an object around the cameras field of vision and
track it's real location with the screen position.  You make up a grid of
mappings, and when you are done you just interpolate between all the
points so you end up with a matrix of screen to position values.  The
studie found that if youi are just interpolating between small areas of
the screen, a simple linear model works perfectly, no fancy math involved.

USB cable length is an issue, alas.  And wireless cameras are not exactly
cheap to throw half a dozen around to cover the yard if it stretches
around your entire house.

Hmm.

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[John Coppens]

On Wed, 30 Jul 2008 19:53:05 -0400 (EDT)
piclist@... wrote:

> You make up a grid of
> mappings, and when you are done you just interpolate between all the
> points so you end up with a matrix of screen to position values.

Yes... The thing is that 640x480 cameras don't give much leeway to
interpolate, less if you look at an angle. That's what I meant in the
reply.

Given the relative slowness of the machine, cheap still cameras
could work with better resolution. Leaves the USB problem. There are
Ethernet cams too, but cost is similar to wireless.

John
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[Apptech]

> Anybody know of a website or links to a cheap beacon
> system
> for postion location for a mobile robot ?  I looked around
> the net and everything was pretty expensive.

Somewhat internally redundant content follows ...

LineS of sight  may work for you.

Mower has a modulated tx beacon and eg rotating sensors at
various points that deduce the angle to the beacon. You
require enough sensors such that 3 can always see the mower.
You can also have multiple stationary senders and a single
scanning receiver on the mower. Probably cheaper and easier.
TX's could be coded eg IR sources but with care you may be
able to use simple uncoded omnidirectional sources and some
extra information from knowing the beacon position
relationships.

If you use RF AND you can "see" through the building then
you can use radio direction finding - probably again with a
rotating sensor. If you can't 'see' through the building
then placing more sensors, with some outside the covered
area if necessary, allows lines of sight / RF that never
intersect the building.

Simple variant. Spinning IR "line of light" mounted on tower
(just a pole would do) high above the house so it 'looks
down' on mower. A detector on the mower and a knowledge of
tx position tells where the mower is on an angle around the
house. A second tx on another tall tower (tree, power on
fence etc) does similarly. Maybe a few of these on boundary
only. Turns back into original system with enough beacons.

You can also implement (as some have) a multi transmitter
phase measurement system to create your won GPS style
system. Not for the faint hearted.



        R
 

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[Cedric Chang-2]

Robin
Very cool demo of infrared dot tracking
Thanks
cc

> On Jul 30, 2008, at 4:30 PM, Robin D. Bussell wrote:
>
>
>
>
>> Another idea is a beacon like an IR led on the robot, and cheap USB
>> cameras looking down.  From the position of the LED in the camera's
> view
>> you can easily calculate it's position.  A system to do just that us
> used
>> to track foul balls in tennis.
>
> Maybe this chap's wii remote hacking projects will be of use, he's
> tracking things very well:
>
> http://www.cs.cmu.edu/~johnny/projects/wii/
>
> Although you'd need a PC or similar with Bluetooth on the mower I
> suppose... does the mower need to know where it is or does an outside
> control system need to track the mower?
>
> Cheers,
>      Robin.
>
> P.S. the stuff on this page is fantastic! (though nothing of any  
> use for
> lawnmower tracking :)  )
>
> http://www.cs.cmu.edu/~johnny/projects/thesis/

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[Forrest W Christian-2]

A few "brainstorming" thoughts...

The big one:  Make the rover as dumb as possible.  Putting this
intelligence in the mower is silly...  Build this in an older PC or
similar, and then have the radio control simply provide direction to the
mower.   That is, the PC will determine where the mower is now, and
where it needs to go, and tell the mower to move say left or right or
forward or backward.

So, then you simply have to know where the rover is, within a few
inches.  Ideas:

1) Use radio direction finding.   Place a "beacon" on the mower - just a
transmitter on a specific frequency, no modulation or anything.   In the
yard area place one or more receivers which can detect phasing
differences between two antennas.   The simplest way to do this is with
a pair of antennas and an antenna switch to switch between them, hooked
into a FM receiver on the same frequency.    With suitable signal
processing, this will give you an angle from the antenna where the rover is.

2) Use high resolution video and some sort of video processing...  You
will need to ensure something like 1 inch per pixel or similar and then
write some code to locate the mower.  You should be able to make this
easy to locate by painting it fluorescent orange or similar.   Of note,
a 1024x768 camera should be able to handle an 85x64 ft yard if you can
mount it in the right spot and one inch per pixel is sufficient
resolution (subject to experimentation).  These are commonly available
for less than $40 in the form of a USB webcam.   I think this is where I
would start..  The loop would look something like: grab a picture, look
for orange.  Figure out where it is in relation to where it needs to
be.  Command the mower. Repeat.

-forrest
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[Doug Metzler-4]

I've got a solar charging solution that runs a small circuit.  It uses a
single 1.2v NiMH battery and my goal is to maximize the NiMH cycles.  

 

I got one of these slick little voltage supervisory chips:

 

http://www.mouser.com/Search/ProductDetail.aspx?qs=%2fugrpAKHX8rrqC4E3QUSBg%
3d%3d

 

That triggers at 1.1v - thus shutting off my circuit as soon as the NiMH
battery gets to the steep part of the discharge curve.

 

The supervisory drives a 2N2222 to pull the circuit to ground.

 

The problem is that as soon as the device triggers and shuts down the
circuit the voltage in the battery climbs back up to 1.2v and the circuit
turns back on, pulling the battery down below 1.1 so it turns off, and
repeats this probably a dozen times before finally settling below the
threshold

 

Is there a simple analog circuit I could wrap around the 2222 to keep it
pulled down for several hours even if the supervisory turns on and off?

 

Keep in mind that I don't have a uController available.  (although if I
could find a very inexpensive 1.2v controller that might be a solution).

 

Thank you,

 

DougM

 

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[Forrest W Christian-2]

I'd switch the 2n2222 for a 2n7000. This will eliminate the B-E drain
through the 2n2222, and permit the use of a simple r/c network on the
gate of the 2n7000 to achieve the delay.   Plus, it should be more
efficient without the B-E current.

I'd probably start with the open drain output version of the supervisory
circuit, and connect it from the gate to ground.   Put a capacitor in
parallel (also from gate to ground).   Add a high-value pull up resistor
to +V.

That way, when it triggers, it will yank the gate to ground, turning off
the 2n7000.   When it "untriggers", the capacitor will slowly charge
through the pullup until it reaches the gate threshold, at which point
the 2n7000 will turn back on.    

-forrest

Doug Metzler wrote:

> I've got a solar charging solution that runs a small circuit.  It uses a
> single 1.2v NiMH battery and my goal is to maximize the NiMH cycles.  
>
>  
>
> I got one of these slick little voltage supervisory chips:
>
>  
>
> http://www.mouser.com/Search/ProductDetail.aspx?qs=%2fugrpAKHX8rrqC4E3QUSBg%
> 3d%3d
>
>  
>
> That triggers at 1.1v - thus shutting off my circuit as soon as the NiMH
> battery gets to the steep part of the discharge curve.
>
>  
>
> The supervisory drives a 2N2222 to pull the circuit to ground.
>
>  
>
> The problem is that as soon as the device triggers and shuts down the
> circuit the voltage in the battery climbs back up to 1.2v and the circuit
> turns back on, pulling the battery down below 1.1 so it turns off, and
> repeats this probably a dozen times before finally settling below the
> threshold
>
>  
>
> Is there a simple analog circuit I could wrap around the 2222 to keep it
> pulled down for several hours even if the supervisory turns on and off?
>
>  
>
> Keep in mind that I don't have a uController available.  (although if I
> could find a very inexpensive 1.2v controller that might be a solution).
>
>  
>
> Thank you,
>
>  
>
> DougM
>
>  
>
>  

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[Bob Blick-4]

Probably need something more modern with a lower gate threshold than the
'7000 since isn't this all running on 1.2 volts?

Cheerful regards,

Bob

Forrest Christian wrote:

> I'd switch the 2n2222 for a 2n7000. This will eliminate the B-E drain
> through the 2n2222, and permit the use of a simple r/c network on the
> gate of the 2n7000 to achieve the delay.   Plus, it should be more
> efficient without the B-E current.
>
> I'd probably start with the open drain output version of the supervisory
> circuit, and connect it from the gate to ground.   Put a capacitor in
> parallel (also from gate to ground).   Add a high-value pull up resistor
> to +V.
>
> That way, when it triggers, it will yank the gate to ground, turning off
> the 2n7000.   When it "untriggers", the capacitor will slowly charge
> through the pullup until it reaches the gate threshold, at which point
> the 2n7000 will turn back on.    
>
> -forrest
>
> Doug Metzler wrote:
>> I've got a solar charging solution that runs a small circuit.  It uses a
>> single 1.2v NiMH battery and my goal is to maximize the NiMH cycles.  
>>
>>  
>>
>> I got one of these slick little voltage supervisory chips:
>>
>>  
>>
>> http://www.mouser.com/Search/ProductDetail.aspx?qs=%2fugrpAKHX8rrqC4E3QUSBg%
>> 3d%3d
>>
>>  
>>
>> That triggers at 1.1v - thus shutting off my circuit as soon as the NiMH
>> battery gets to the steep part of the discharge curve.
>>
>>  
>>
>> The supervisory drives a 2N2222 to pull the circuit to ground.
>>
>>  
>>
>> The problem is that as soon as the device triggers and shuts down the
>> circuit the voltage in the battery climbs back up to 1.2v and the circuit
>> turns back on, pulling the battery down below 1.1 so it turns off, and
>> repeats this probably a dozen times before finally settling below the
>> threshold
>>
>>  
>>
>> Is there a simple analog circuit I could wrap around the 2222 to keep it
>> pulled down for several hours even if the supervisory turns on and off?
>>
>>  
>>
>> Keep in mind that I don't have a uController available.  (although if I
>> could find a very inexpensive 1.2v controller that might be a solution).
>>
>>  
>>
>> Thank you,
>>
>>  
>>
>> DougM
>>
>>  
>>
>>  
>

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[Apptech]

> I got one of these slick little voltage supervisory chips:
> http://www.mouser.com/Search/ProductDetail.aspx?qs=%2fugrpAKHX8rrqC4E3QUSBg%
> 3d%3d

> That triggers at 1.1v - thus shutting off my circuit as
> soon as the NiMH
> battery gets to the steep part of the discharge curve.
> The supervisory drives a 2N2222 to pull the circuit to
> ground.

> The problem is that as soon as the device triggers and
> shuts down the
> circuit the voltage in the battery climbs back up to 1.2v
> and the circuit
> turns back on, pulling the battery down below 1.1 so it
> turns off, and
> repeats this probably a dozen times before finally
> settling below the
> threshold

> Is there a simple analog circuit I could wrap around the
> 2222 to keep it
> pulled down for several hours even if the supervisory
> turns on and off?

Data sheet

        http://www.onsemi.com/pub_link/Collateral/NCP304-D.PDF

One way is to add hysteresis to the sensed voltage.

A simple way (that possibly works) is to add a series
resistor to the sense IC input / power supply.
When operated it's current drain will rise, thereby
decreasing the input voltage. Consult data sheet and add an
appropriate R.

Too large and it won't rewake well when voltage rises.

For extra points and more complexity you could have a
voltage divider at the input with the transistor adding to
the loading. More points from using a time delay (aka
capacitor) to make the extra load fully or partially time
dependant.

Just the series R will probably help.



        Russell


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[Walter Banks]

You may want to rethink the problem a little when it comes to
GPS. You don't need to know the absolute position of the lawn
mower only that cuts the whole yard and not one segment and
it is in your yard.

w..


Kevin wrote:

> Anybody know of a website or links to a cheap beacon system
> for postion location for a mobile robot ?  I looked around
> the net and everything was pretty expensive.
>
> I was thinking of trying to use those cheap 315 mhz tx/rx
> modules. I want to be able to postion an autonomous lawn
> mower within 6 inches or so. I have an acre lot with a house in the
> center so line of site is out.
>
> I have a GPS receiver but that is only good to ten feet
> with WAAS enabled.
>
> Any other suggestions ?
>
> Thanks,
> Kevin
>
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[Forrest W Christian-2]

Yeah, you're right...     I think my brain was stuck on the 2n2222 B-E
voltage drop for some reason, and not the 2V-ish typical threshold of a
2n7000.   I'll claim sleep deprivation as my excuse (only ~4-5 hours
last night).

That said I'm sure Zetex (and others) have a suitable low-threshold fet
which should work for the application as described.

-forrest

Bob Blick wrote:

> Probably need something more modern with a lower gate threshold than the
> '7000 since isn't this all running on 1.2 volts?
>
> Cheerful regards,
>
> Bob
>
> Forrest Christian wrote:
>  
>> I'd switch the 2n2222 for a 2n7000. This will eliminate the B-E drain
>> through the 2n2222, and permit the use of a simple r/c network on the
>> gate of the 2n7000 to achieve the delay.   Plus, it should be more
>> efficient without the B-E current.
>>
>> I'd probably start with the open drain output version of the supervisory
>> circuit, and connect it from the gate to ground.   Put a capacitor in
>> parallel (also from gate to ground).   Add a high-value pull up resistor
>> to +V.
>>
>> That way, when it triggers, it will yank the gate to ground, turning off
>> the 2n7000.   When it "untriggers", the capacitor will slowly charge
>> through the pullup until it reaches the gate threshold, at which point
>> the 2n7000 will turn back on.    
>>
>> -forrest
>>
>> Doug Metzler wrote:
>>    
>>> I've got a solar charging solution that runs a small circuit.  It uses a
>>> single 1.2v NiMH battery and my goal is to maximize the NiMH cycles.  
>>>
>>>  
>>>
>>> I got one of these slick little voltage supervisory chips:
>>>
>>>  
>>>
>>> http://www.mouser.com/Search/ProductDetail.aspx?qs=%2fugrpAKHX8rrqC4E3QUSBg%
>>> 3d%3d
>>>
>>>  
>>>
>>> That triggers at 1.1v - thus shutting off my circuit as soon as the NiMH
>>> battery gets to the steep part of the discharge curve.
>>>
>>>  
>>>
>>> The supervisory drives a 2N2222 to pull the circuit to ground.
>>>
>>>  
>>>
>>> The problem is that as soon as the device triggers and shuts down the
>>> circuit the voltage in the battery climbs back up to 1.2v and the circuit
>>> turns back on, pulling the battery down below 1.1 so it turns off, and
>>> repeats this probably a dozen times before finally settling below the
>>> threshold
>>>
>>>  
>>>
>>> Is there a simple analog circuit I could wrap around the 2222 to keep it
>>> pulled down for several hours even if the supervisory turns on and off?
>>>
>>>  
>>>
>>> Keep in mind that I don't have a uController available.  (although if I
>>> could find a very inexpensive 1.2v controller that might be a solution).
>>>
>>>  
>>>
>>> Thank you,
>>>
>>>  
>>>
>>> DougM
>>>
>>>  
>>>
>>>  
>>>      

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[Kevin-40]

On Thu, 31 Jul 2008, Walter Banks wrote:

Some good brainstorming ideas !  Couple of issues I  should
mention, I don't think I could get a camera looking down
because of several large trees in the yard. Also, the yard
is half level, the other half has a fall of probably 10 ft
in 60 ft. So, one section is a steep hill. That may be
a problem for a transmitter pole or sensor on top of the
mower.

I plan on making the mower as dumb as possible. I will have
my computer perform the processing and relay course and
direction to the mower through my wifi network or something
similiar (zigbee, bluetooth, etc...).

Thanks,
Kevin

> You may want to rethink the problem a little when it comes to
> GPS. You don't need to know the absolute position of the lawn
> mower only that cuts the whole yard and not one segment and
> it is in your yard.
>
> w..
>
>
> Kevin wrote:
>
>> Anybody know of a website or links to a cheap beacon system
>> for postion location for a mobile robot ?  I looked around
>> the net and everything was pretty expensive.
>>
>> I was thinking of trying to use those cheap 315 mhz tx/rx
>> modules. I want to be able to postion an autonomous lawn
>> mower within 6 inches or so. I have an acre lot with a house in the
>> center so line of site is out.
>>
>> I have a GPS receiver but that is only good to ten feet
>> with WAAS enabled.
>>
>> Any other suggestions ?
>>
>> Thanks,
>> Kevin
>>

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[M. Adam Davis-2]

Your yard sounds like it has a number of interesting topological
features!  I wonder if you could put a triple axis accelerometer and
triple axis magnetometer in the mower to get the vector of the ground
surface and the magnetic field.  If you map out your entire yard you
may find that between those two vectors you can roughly identify the
location of the mower.  Place some large metal or magnetic objects
underground in areas where the sloping is not so great.  Or put
magnetic loops underground with time-varying fields.  Turn your yard
into a giant Wacom tablet!

I like the ultrasonic transducers idea, though.  There's a lot of
literature out there about using ultrasonic transducers for measuring
distance.  All you need (heh heh heh - there's that trivializing
phrase again!) is to place a dozen transducers around the yard, each
listening to each other and transmitting a code at a particular time.
Since they can be synchronized to each other, then you can gaurantee
that no transitter will be transmitting at the same time as another
(time slots).

The robot can hear at least 4 at any given time, and reflections can
be dealt with by only paying attention to the first sound heard.  If a
reflection is messing up one of the transmissions, there's lots of
redundancy, so you can safely ignore that one.

Since they can hear each other, wind speed, direction, and temperature
can all be calculated and accounted for on a per measurment basis.

Or reverse that and have the robot beep with transducers around the
yard picking the sound up - but then you'll need auxiliary beeps to
determine wind speed, direction, and temperature.

Fun stuff to think about...

-Adam

On 7/31/08, Kevin <kben@...> wrote:

> On Thu, 31 Jul 2008, Walter Banks wrote:
>
> Some good brainstorming ideas !  Couple of issues I  should
> mention, I don't think I could get a camera looking down
> because of several large trees in the yard. Also, the yard
> is half level, the other half has a fall of probably 10 ft
> in 60 ft. So, one section is a steep hill. That may be
> a problem for a transmitter pole or sensor on top of the
> mower.
>
> I plan on making the mower as dumb as possible. I will have
> my computer perform the processing and relay course and
> direction to the mower through my wifi network or something
> similiar (zigbee, bluetooth, etc...).
>
> Thanks,
> Kevin
>
>
> > You may want to rethink the problem a little when it comes to
> > GPS. You don't need to know the absolute position of the lawn
> > mower only that cuts the whole yard and not one segment and
> > it is in your yard.
> >
> > w..
> >
> >
> > Kevin wrote:
> >
> >> Anybody know of a website or links to a cheap beacon system
> >> for postion location for a mobile robot ?  I looked around
> >> the net and everything was pretty expensive.
> >>
> >> I was thinking of trying to use those cheap 315 mhz tx/rx
> >> modules. I want to be able to postion an autonomous lawn
> >> mower within 6 inches or so. I have an acre lot with a house in the
> >> center so line of site is out.
> >>
> >> I have a GPS receiver but that is only good to ten feet
> >> with WAAS enabled.
> >>
> >> Any other suggestions ?
> >>
> >> Thanks,
> >> Kevin
> >>
>
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[Forrest W Christian-2]

On the camera thing...  Nothing precludes you from using several cameras
scattered around...perhaps linked back to the base using wireless
transmissions.    Same with other location ideas.

Kevin wrote:

> On Thu, 31 Jul 2008, Walter Banks wrote:
>
> Some good brainstorming ideas !  Couple of issues I  should
> mention, I don't think I could get a camera looking down
> because of several large trees in the yard. Also, the yard
> is half level, the other half has a fall of probably 10 ft
> in 60 ft. So, one section is a steep hill. That may be
> a problem for a transmitter pole or sensor on top of the
> mower.
>
> I plan on making the mower as dumb as possible. I will have
> my computer perform the processing and relay course and
> direction to the mower through my wifi network or something
> similiar (zigbee, bluetooth, etc...).
>
> Thanks,
> Kevin
>
>
>  
>> You may want to rethink the problem a little when it comes to
>> GPS. You don't need to know the absolute position of the lawn
>> mower only that cuts the whole yard and not one segment and
>> it is in your yard.
>>
>> w..
>>
>>
>> Kevin wrote:
>>
>>    
>>> Anybody know of a website or links to a cheap beacon system
>>> for postion location for a mobile robot ?  I looked around
>>> the net and everything was pretty expensive.
>>>
>>> I was thinking of trying to use those cheap 315 mhz tx/rx
>>> modules. I want to be able to postion an autonomous lawn
>>> mower within 6 inches or so. I have an acre lot with a house in the
>>> center so line of site is out.
>>>
>>> I have a GPS receiver but that is only good to ten feet
>>> with WAAS enabled.
>>>
>>> Any other suggestions ?
>>>
>>> Thanks,
>>> Kevin
>>>
>>>      
>
>  

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[Apptech]

- A wire grid would relatively easy to install ("mole plow"
insertion) and probably as easy and accurate to drive as any
other system.

- A small UAV

1     flies a search grid looking for the mower.
or
2     carries a camera which views the mover and targets for
location.

- A hot air ballon on a cable, powerd by a heater which
allows it to always stay aloft ...

- Hmm.
  Mower.
  Microphones mounted on the house ... .

- An ultrasonic ranger on the mower identifies IR beacons
and calculates their distance.
or
Utrasonic rangers detect the mowers location using a beacon
on the mower.

- A ...

Sounds like fun.

____________________________

If somebody wanted me to show them a demo working within a
week I'd consider going for the mower carrying a rotating
optical detector with N modulated beacons. Demos in no time
are easy. Making the final product work is another matter.



        R





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