AVR-Chat

----- Original Message ----- 

From: "Bernd Felsche" <bernie@innovative.iinet.net.au>
To: <AVR-Chat@yahoogroups.com>
Sent: Wednesday, December 15, 2004 4:06 PM
Subject: [AVR-Chat] Radio servo for analogue indicator?


>
> I'm considering all sorts of low-power options for providing an
> analogue indication (moving needle or bar). Typical ammeters draw
> current and the quantity I want to indicate isn't directly available
> as a current... it's number-crunched. Scale will be semi-log.
>
> At first, I looked at small stepper motors but they're simply
> over-kill.  During my search, I've stumbled across radio-control
> servos... which are quite popular in robotics and the driving
> technology is certainly well known in AVR circles.
>
> The question is; has anybody used these servos for instrumentation?
>
> The accuracy doesn't need to be high; it only needs to provide an
> at-a-glance feel for the operator. The indicator only needs to be
> "accurate" at one point, which could be calibrated at "boot time".
> I expect the AVR controlling the servo to have a table of position
> vs value... with linear interpolation for points inbetween.
>
> Any pointers to useful information such as steady-state current,
> holding torques, etc will be appreciated. I Googled but got around a
> million hits... or none.

How about a voltmeter driven with PWM, or a simple DAC?

I think that the Kawasaki Hayabusa motorbike uses servo motors for the 
speedo and rev counter. When the ignition is switched on and the bike does a 
self-test, both sets of needles rotate rapidly for a few seconds.

Leon

I'm considering all sorts of low-power options for providing an
analogue indication (moving needle or bar). Typical ammeters draw
current and the quantity I want to indicate isn't directly available
as a current... it's number-crunched. Scale will be semi-log.

At first, I looked at small stepper motors but they're simply
over-kill.  During my search, I've stumbled across radio-control
servos... which are quite popular in robotics and the driving
technology is certainly well known in AVR circles.

The question is; has anybody used these servos for instrumentation?

The accuracy doesn't need to be high; it only needs to provide an
at-a-glance feel for the operator. The indicator only needs to be
"accurate" at one point, which could be calibrated at "boot time".
I expect the AVR controlling the servo to have a table of position
vs value... with linear interpolation for points inbetween.

Any pointers to useful information such as steady-state current,
holding torques, etc will be appreciated. I Googled but got around a
million hits... or none.

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
\ /  ASCII ribbon campaign | I'm a .signature virus!
 X   against HTML mail     | Copy me into your ~/.signature
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If you want low power how about a graphical LCD
display (mobile phone display for example) emulating a
needle or a moving bar? A Nokia 3310 LCD (for example)
would give you 48x84 pixels for not a lot of money.

ken

 --- Bernd Felsche <bernie@innovative.iinet.net.au>
wrote: 
> 
> I'm considering all sorts of low-power options for
> providing an
> analogue indication (moving needle or bar). Typical
> ammeters draw
> current and the quantity I want to indicate isn't
> directly available
> as a current... it's number-crunched. Scale will be
> semi-log.
> 
> At first, I looked at small stepper motors but
> they're simply
> over-kill.  During my search, I've stumbled across
> radio-control
> servos... which are quite popular in robotics and
> the driving
> technology is certainly well known in AVR circles.
> 
> The question is; has anybody used these servos for
> instrumentation?
> 
> The accuracy doesn't need to be high; it only needs
> to provide an
> at-a-glance feel for the operator. The indicator
> only needs to be
> "accurate" at one point, which could be calibrated
> at "boot time".
> I expect the AVR controlling the servo to have a
> table of position
> vs value... with linear interpolation for points
> inbetween.
> 
> Any pointers to useful information such as
> steady-state current,
> holding torques, etc will be appreciated. I Googled
> but got around a
> million hits... or none.
> 
> -- 
> /"\ Bernd Felsche - Innovative Reckoning, Perth,
> Western Australia
> \ /  ASCII ribbon campaign | I'm a .signature virus!
>  X   against HTML mail     | Copy me into your
> ~/.signature
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> 
> 
> 
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Bernd, 

those servos draw quite a lot of current - especially while they move,
are we talking of some 200 mA or so - in that respect a classic ammeter
would be the better choice I guess. 

Cheers, Gert Mueller

-----------------------------------------------------------
Datentechnik Dr.Gert Mueller GmbH
Diezstraße 2a,   D-53113 Bonn
Tel: +49-228-217297 Fax +49-228-261387
EMail: info@stepwalk.de
Homepage: www.stepwalk.de

> 
> I'm considering all sorts of low-power options for providing an
> analogue indication (moving needle or bar). Typical ammeters draw
> current and the quantity I want to indicate isn't directly available
> as a current... it's number-crunched. Scale will be semi-log.
> 
> At first, I looked at small stepper motors but they're simply
> over-kill.  During my search, I've stumbled across radio-control
> servos... which are quite popular in robotics and the driving
> technology is certainly well known in AVR circles.
> 
> The question is; has anybody used these servos for instrumentation?
> 
> The accuracy doesn't need to be high; it only needs to provide an
> at-a-glance feel for the operator. The indicator only needs to be
> "accurate" at one point, which could be calibrated at "boot time".
> I expect the AVR controlling the servo to have a table of position
> vs value... with linear interpolation for points inbetween.
> 
> Any pointers to useful information such as steady-state current,
> holding torques, etc will be appreciated. I Googled but got around a
> million hits... or none.
> 
> -- 
> /"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
> \ /  ASCII ribbon campaign | I'm a .signature virus!
>  X   against HTML mail     | Copy me into your ~/.signature
> / \  and postings          | to help me spread!
> 
> 
> 
> 
> ------------------------ Yahoo! Groups Sponsor 
> --------------------~--> 
> Make a clean sweep of pop-up ads. Yahoo! Companion Toolbar.
> Now with Pop-Up Blocker. Get it for free!
> http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/dN_tlB/TM
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> ------~-> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>

Have you considered LED's?  If they would work in your
application, they'd be easier to prototype, respond
more quickly and probably less expensive.

Several times, I've thought about using a stepper as a
Tach indicator, but the LED's response speed is too
large an advantage.  An RC servo would be even slower.

The one big disadvantage LED's have is not being able
to be seen in strong light.

Jeff Engel
--- Bernd Felsche <bernie@innovative.iinet.net.au>
wrote:

> 
> I'm considering all sorts of low-power options for
> providing an
> analogue indication (moving needle or bar). Typical
> ammeters draw
> current and the quantity I want to indicate isn't
> directly available
> as a current... it's number-crunched. Scale will be
> semi-log.
> 
> At first, I looked at small stepper motors but
> they're simply
> over-kill.  During my search, I've stumbled across
> radio-control
> servos... which are quite popular in robotics and
> the driving
> technology is certainly well known in AVR circles.
> 
> The question is; has anybody used these servos for
> instrumentation?
> 
> The accuracy doesn't need to be high; it only needs
> to provide an
> at-a-glance feel for the operator. The indicator
> only needs to be
> "accurate" at one point, which could be calibrated
> at "boot time".
> I expect the AVR controlling the servo to have a
> table of position
> vs value... with linear interpolation for points
> inbetween.
> 
> Any pointers to useful information such as
> steady-state current,
> holding torques, etc will be appreciated. I Googled
> but got around a
> million hits... or none.
> 
> -- 
> /"\ Bernd Felsche - Innovative Reckoning, Perth,
> Western Australia
> \ /  ASCII ribbon campaign | I'm a .signature virus!
>  X   against HTML mail     | Copy me into your
> ~/.signature
> / \  and postings          | to help me spread!
> 
> 
> 
> 
> ------------------------ Yahoo! Groups Sponsor
> --------------------~--> 
> Make a clean sweep of pop-up ads. Yahoo! Companion
> Toolbar.
> Now with Pop-Up Blocker. Get it for free!
>
http://us.click.yahoo.com/L5YrjA/eSIIAA/yQLSAA/dN_tlB/TM
>
--------------------------------------------------------------------~->
> 
> 
>  
> Yahoo! Groups Links
> 
> 
>     AVR-Chat-unsubscribe@yahoogroups.com
> 
>  
> 
> 
> 
> 


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Bernd Felsche said:
>
> I'm considering all sorts of low-power options for providing an
> analogue indication (moving needle or bar). Typical ammeters draw
> current and the quantity I want to indicate isn't directly available as
> a current... it's number-crunched. Scale will be semi-log.
>
> At first, I looked at small stepper motors but they're simply
> over-kill.  During my search, I've stumbled across radio-control
> servos... which are quite popular in robotics and the driving
> technology is certainly well known in AVR circles.

At the risk of showing my age, does no one remember moving coil meters
anymore?

See: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/galvan.html#c1

>
> The question is; has anybody used these servos for instrumentation?
>
> The accuracy doesn't need to be high; it only needs to provide an
> at-a-glance feel for the operator. The indicator only needs to be
> "accurate" at one point, which could be calibrated at "boot time". I
> expect the AVR controlling the servo to have a table of position vs
> value... with linear interpolation for points inbetween.

You should be able to create any sort of scale you want with the AVR
driving it.  They typically require very little current.


Mike

On Thursday 16 December 2004 01:39, Jeffrey Engel wrote:

> --- Bernd Felsche <bernie@innovative.iinet.net.au>
> wrote:
> > I'm considering all sorts of low-power options for providing an
> > analogue indication (moving needle or bar). Typical ammeters
> > draw current and the quantity I want to indicate isn't directly
> > available as a current... it's number-crunched. Scale will be
> > semi-log.

> > At first, I looked at small stepper motors but they're simply
> > over-kill.  During my search, I've stumbled across radio-control
> > servos... which are quite popular in robotics and the driving
> > technology is certainly well known in AVR circles.

> Have you considered LED's?  If they would work in your
> application, they'd be easier to prototype, respond
> more quickly and probably less expensive.

LED's are in use at the moment, but useless under nominal lighting
conditions. Bright daylight.

> Several times, I've thought about using a stepper as a
> Tach indicator, but the LED's response speed is too
> large an advantage.  An RC servo would be even slower.

> The one big disadvantage LED's have is not being able
> to be seen in strong light.

You got it in one. 

-- 
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On Thursday 16 December 2004 00:16, KEN HUNT wrote:

> wrote:
> > I'm considering all sorts of low-power options for providing an
> > analogue indication (moving needle or bar). Typical ammeters
> > draw current and the quantity I want to indicate isn't directly
> > available as a current... it's number-crunched. Scale will be
> > semi-log.

> If you want low power how about a graphical LCD
> display (mobile phone display for example) emulating a
> needle or a moving bar? A Nokia 3310 LCD (for example)
> would give you 48x84 pixels for not a lot of money.

Two factors: The LCD requires much more glue to drive and secondly
most LCD give up the ghost at the ambient operating temperatures
that may exceed 45 degrees C.

-- 
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On Dec 15, 2004, at 10:19 AM, Leon Heller wrote:

> I think that the Kawasaki Hayabusa motorbike uses servo motors for the
> speedo and rev counter. When the ignition is switched on and the bike 
> does a
> self-test, both sets of needles rotate rapidly for a few seconds.

The Hayabusa is a Suzuki.  :-)

These days most vehicles use electronic meters because the electronics 
are less expensive and more reliable than mechanical.

If one wishes a simple indicator then R/C servos would be a good 
choice. "Real" meters are expensive!

As nothing but an indicator one doesn't need any holding torque other 
than existing internal friction. As for power and current consumption 
once one has the desired indication then simply quit driving the servo. 
It will stay put.

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.

On Thursday 16 December 2004 01:51, Mike Murphree wrote:
> Bernd Felsche said:
> > I'm considering all sorts of low-power options for providing an
> > analogue indication (moving needle or bar). Typical ammeters draw
> > current and the quantity I want to indicate isn't directly available as
> > a current... it's number-crunched. Scale will be semi-log.

> > At first, I looked at small stepper motors but they're simply
> > over-kill.  During my search, I've stumbled across radio-control
> > servos... which are quite popular in robotics and the driving
> > technology is certainly well known in AVR circles.

> At the risk of showing my age, does no one remember moving coil meters
> anymore?

Sure do! 

> See: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/galvan.html#c1

> > The question is; has anybody used these servos for instrumentation?

> > The accuracy doesn't need to be high; it only needs to provide an
> > at-a-glance feel for the operator. The indicator only needs to be
> > "accurate" at one point, which could be calibrated at "boot time". I
> > expect the AVR controlling the servo to have a table of position vs
> > value... with linear interpolation for points inbetween.

> You should be able to create any sort of scale you want with the AVR
> driving it.  They typically require very little current.

The indicator is for a "power balance" display in a solar car.  It
will be subjected to vibration as well as high ambient temperatures.
IIRC, the moving coil meters don't typically like that sort of
thing.

I'm not sure of all the options available to drive one to display
the quantities (PWM would depend on the mechanical response) ... and
finding one with a highly-visible needle is another task altogether.

Response time isn't that critical. As long as the full scale can be
traversed in about half a second or less, that's fast enough. I
intend to only show a moving average over one or two seconds anyway,
otherwise the display gets "too busy", causing the driver to make
many adjustments over time which aren't really necessary.

-- 
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\ /  ASCII ribbon campaign | I'm a .signature virus!
 X   against HTML mail     | Copy me into your ~/.signature
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On Thursday 16 December 2004 00:27, Gert Mueller wrote:

> those servos draw quite a lot of current - especially while they move,

That's why I wouldn't move it very often, nor far, most of the time.
The load against which it'd move would be close to zero.

Any idea of the current draw if the position isn't changing?
That's the sort of information I'm looking for.

> are we talking of some 200 mA or so - in that respect a classic ammeter
> would be the better choice I guess.

Except the environment (solar car) isn't very friendly to it; and
it's almost nominal operating conditions for the servo.

-- 
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\ /  ASCII ribbon campaign | I'm a .signature virus!
 X   against HTML mail     | Copy me into your ~/.signature
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Bernd;

IIRC, the RC servos take a 0.5ms to 1.5ms pulse input
at about TTL levels.  If you're really strapped for
power, you could always power it down until the
reading needs to change.

The pointer could be something simple made from
pastic, like a disk with the 'needle' drawn on with a
marker.  Naturally, once you're convinced it will work
you could fab up something more elegant.

Sounds like a good match for your application.

Disclaimer: I'm not into R/C and going from an
increasingly faulty memory. . .

Jeff Engel
--- Bernd Felsche <bernie@innovative.iinet.net.au>
wrote:

> At first, I looked at small stepper motors but
> they're simply
> > > over-kill.  During my search, I've stumbled
> across radio-control
> > > servos... which are quite popular in robotics
> and the driving
> > > technology is certainly well known in AVR
> circles.


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Make that 'plastic'. . .

Jeff
--- Jeffrey Engel <jengeltx@yahoo.com> wrote:

> The pointer could be something simple made from
> pastic, like a disk with the 'needle' drawn on with
> a
> marker.  Naturally, once you're convinced it will
> work
> you could fab up something more elegant.


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> LED's are in use at the moment, but useless under nominal lighting
> conditions. Bright daylight.

There are a variety of very bright daylight-visible LEDs on the market.
Some output hundreds of mcd in only tens of milliamps. 

Consider this option - arrange six high output bi-color (red-green) LEDs
in a line. Use the PWM capability of the MSP430 to drive each of them.
As the indicator "rises", first the LED begins to glow green, then
becomes a brighter green, then the PWM begins to introduce red. As more
red is proportionally added, the color changes from green to yellowish.
At 50/50, the LED appears yellow. Then, as the indication continues to
rise, the light begins to appear more and more orange, then red. 

This would have sort of a "VU meter effect" and would be very good for
at-a-glance readings. All functionality could be achieved on-chip.

A quick Digi-Key search returns a high-output red/green LED in a 5mm
case, the Lite-On LTL-293SJW. It outputs 90mcd red, 40mcd green -
intensity will look about the same due to varying spectral sensitivity
of the eye when both are run at 20mA. They are $0.37 each and there are
thousands in stock - might as well pick up a few and try them. At that
price, even if it doesn't work, it's not much invested!

Dave

Whoops...thought this was posted in my MSP430 forum! My bad!

ifdef "Re: [AVR-Chat] Radio servo for analogue indicator?"
#define MSP430 AVR
endif

:)

Dave

On Wed, 2004-12-15 at 22:16, David D. Rea wrote:
> > LED's are in use at the moment, but useless under nominal lighting
> > conditions. Bright daylight.
> 
> There are a variety of very bright daylight-visible LEDs on the market.
> Some output hundreds of mcd in only tens of milliamps. 
> 
> Consider this option - arrange six high output bi-color (red-green) LEDs
> in a line. Use the PWM capability of the MSP430 to drive each of them.
> As the indicator "rises", first the LED begins to glow green, then
> becomes a brighter green, then the PWM begins to introduce red. As more
> red is proportionally added, the color changes from green to yellowish.
> At 50/50, the LED appears yellow. Then, as the indication continues to
> rise, the light begins to appear more and more orange, then red. 
> 
> This would have sort of a "VU meter effect" and would be very good for
> at-a-glance readings. All functionality could be achieved on-chip.
> 
> A quick Digi-Key search returns a high-output red/green LED in a 5mm
> case, the Lite-On LTL-293SJW. It outputs 90mcd red, 40mcd green -
> intensity will look about the same due to varying spectral sensitivity
> of the eye when both are run at 20mA. They are $0.37 each and there are
> thousands in stock - might as well pick up a few and try them. At that
> price, even if it doesn't work, it's not much invested!
> 
> Dave
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>

David D. Rea wrote:

> Whoops...thought this was posted in my MSP430 forum! My bad!
> 
> ifdef "Re: [AVR-Chat] Radio servo for analogue indicator?"
> #define MSP430 AVR
> endif
> 
> :)
> 
> Dave

Lol is ok mate, would you share the link to the MSP list ? as I would 
like to join one day as I have a stack of MSP's sitting here, just never 
had the chance to play with them :(

Regards,

Kat.

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On Dec 15, 2004, at 6:58 PM, Bernd Felsche wrote:

> Any idea of the current draw if the position isn't changing?
> That's the sort of information I'm looking for.

If your pulse timing varies or the servo is worn or cheap then it will 
"hunt" while not moving and consume a lot of current.

On the other hand once its in the position you desire then not only 
quit driving the position pulse but remove the power entirely from the 
servo. It will stay where you left it and require a modest amount of 
force to budge.

IIRC the position pulse was 1.0 ms to 2.0 ms every 10 ms. Then again 
there were 7 channel analog transmitters and there is only room for 5 
if I remember correctly. The servo is quite forgiving about the 10 ms 
part altho you have to keep sending the pulse until it reaches the 
desired position.

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.

It's another yahoogroup - just go to http://groups.yahoo.com/ and search
for "msp430" - I picked the one with the most members (over 2000)
figuring it'd be the most active... 

Best Regards,
Dave

On Wed, 2004-12-15 at 22:27, Kathy Quinlan wrote:
> David D. Rea wrote:
> 
> > Whoops...thought this was posted in my MSP430 forum! My bad!
> > 
> > ifdef "Re: [AVR-Chat] Radio servo for analogue indicator?"
> > #define MSP430 AVR
> > endif
> > 
> > :)
> > 
> > Dave
> 
> Lol is ok mate, would you share the link to the MSP list ? as I would 
> like to join one day as I have a stack of MSP's sitting here, just never 
> had the chance to play with them :(
> 
> Regards,
> 
> Kat.

>That's why I wouldn't move it very often, nor far, 
>most of the time.
>The load against which it'd move would be close to zero.

>Any idea of the current draw if the position isn't changing?
>That's the sort of information I'm looking for.
 
 
The idle current of common R/C servos is somewhere around 10 - 15 mA.
For detailled info you might check the site www.graupner.de (servo
manufacturer) It's in German - but that shouldn't be a big issue for you
;-) right ?

Cheers, Gert Mueller

On Thursday 16 December 2004 16:27, Gert Mueller wrote:
> >That's why I wouldn't move it very often, nor far,
> >most of the time.
> >The load against which it'd move would be close to zero.

> >Any idea of the current draw if the position isn't changing?
> >That's the sort of information I'm looking for.

> The idle current of common R/C servos is somewhere around 10 - 15
> mA.  For detailled info you might check the site www.graupner.de
> (servo manufacturer) It's in German - but that shouldn't be a big
> issue for you ;-) right ?

Depends on the time of day! :-)

Oooohhh the choice of servos... 4.3g, idle current drain 5 mA. Nice
and light. And digital servos... a bit heavier in both respects as
well as price.

I like the idea of being able disconnect power to simply hold the
position.

It's a whole new world; I'll have to visit an R/C model shop and see
what's available locally.

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
\ /  ASCII ribbon campaign | I'm a .signature virus!
 X   against HTML mail     | Copy me into your ~/.signature
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I thought I might chime in here re LED brightness:
The newer "ultra" bright LEDs, in the 3-7000 mcd range
and can be seen in most daylight conditions when placed
in a dark background or hooded arrangement.  They are still
moderately expensive for the very good ones, about a buck for
green, blue, or white.  Red and yellow LEDs have been very bright
and cheap for some time.  There are no common bi-colors of the
ultras, as yet, and the old red-green are very poor, the green half
is usually dim and yellowish.

Ken


David D. Rea wrote:

>>LED's are in use at the moment, but useless under nominal lighting
>>conditions. Bright daylight.
> 
> 
> There are a variety of very bright daylight-visible LEDs on the market.
> Some output hundreds of mcd in only tens of milliamps. 
> 
> Consider this option - arrange six high output bi-color (red-green) LEDs
> in a line. Use the PWM capability of the MSP430 to drive each of them.
> As the indicator "rises", first the LED begins to glow green, then
> becomes a brighter green, then the PWM begins to int   roducered.Asmore
> red is proportionally added, the color changes from green to yellowish.
> At 50/50, the LED appears yellow. Then, as the indication continues to
> rise, the light begins to appear       moreandmoreorange,thenred.
> 
> This would have sort of a "VU meter effect" and would be very good for
> at-a-glance readings. All functionality could be achieved on-chip.
> 
> A quick Digi-Key search returns a high-output red/green LED in a 5mm
> case, the Lite-On LTL-293SJW. It outputs 90mcd red, 40mcd green -
> intensity will look about the same due to varying spectral sensitivity
> of the eye when both are run at 20mA. They are $0.37 each and there are
> thousands in stock - might as well pick up a few and try them. At that
> price, even if it doesn't work, it's not much invested!
> 
> Dave
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 
>

Here's an on-line demo using an R/C servo that I
stumbled across while looking for something else.

He even has a goofy-looking green pointer hooked to
it!

http://www.ace-lab.com/SCADA/robot.html

HTH,

Jeff Engel


=====
Happiness is - positive intake manifold pressure.


		
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At 04:07 PM 12/16/2004, Jeffrey Engel wrote:


>Here's an on-line demo using an R/C servo that I
>stumbled across while looking for something else.
>
>He even has a goofy-looking green pointer hooked to
>it!
>
>http://www.ace-lab.com/SCADA/robot.html

Cool! Servo wars.
Apparently I got on at the same time someone else did, or their control 
loop is way whacked.

Dave,

When I 'researched' it, there was a significant delay
between control movement and response but seemed
pretty good other than that.

You probably weren't the only person checking it out.

Jeff Engel
--- Dave VanHorn <dvanhorn@dvanhorn.org> wrote:

> 
> At 04:07 PM 12/16/2004, Jeffrey Engel wrote:
> 
> 
> >Here's an on-line demo using an R/C servo that I
> >stumbled across while looking for something else.
> >
> >He even has a goofy-looking green pointer hooked to
> >it!
> >
> >http://www.ace-lab.com/SCADA/robot.html
> 
> Cool! Servo wars.
> Apparently I got on at the same time someone else
> did, or their control 
> loop is way whacked.


=====
Happiness is - positive intake manifold pressure.


		
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The lag time is quite long but it worked for me.

Jim


On Thu, 16 Dec 2004 16:28:38 -0500
 Dave VanHorn <dvanhorn@dvanhorn.org> wrote:
> 
> 
> 
> 
> 
> 
> At 04:07 PM 12/16/2004, Jeffrey Engel wrote:
> 
> 
> >Here's an on-line demo using an R/C servo that I
> >stumbled across while looking for something else.
> >
> >He even has a goofy-looking green pointer hooked to
> >it!
> >
> >http://www.ace-lab.com/SCADA/robot.html
> 
> Cool! Servo wars.
> Apparently I got on at the same time someone else did, or
> their control 
> loop is way whacked.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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How about using a speaks and tones. An AVR chip could more than handle
that. 

-----Original Message-----
From: Bernd Felsche [mailto:bernie@innovative.iinet.net.au] 
Sent: Wednesday, December 15, 2004 7:52 PM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Radio servo for analogue indicator?



On Thursday 16 December 2004 01:51, Mike Murphree wrote:
> Bernd Felsche said:
> > I'm considering all sorts of low-power options for providing an 
> > analogue indication (moving needle or bar). Typical ammeters draw 
> > current and the quantity I want to indicate isn't directly available

> > as a current... it's number-crunched. Scale will be semi-log.

> > At first, I looked at small stepper motors but they're simply 
> > over-kill.  During my search, I've stumbled across radio-control 
> > servos... which are quite popular in robotics and the driving 
> > technology is certainly well known in AVR circles.

> At the risk of showing my age, does no one remember moving coil meters

> anymore?

Sure do! 

> See: 
> http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/galvan.html#c1

> > The question is; has anybody used these servos for instrumentation?

> > The accuracy doesn't need to be high; it only needs to provide an 
> > at-a-glance feel for the operator. The indicator only needs to be 
> > "accurate" at one point, which could be calibrated at "boot time". I

> > expect the AVR controlling the servo to have a table of position vs 
> > value... with linear interpolation for points inbetween.

> You should be able to create any sort of scale you want with the AVR 
> driving it.  They typically require very little current.

The indicator is for a "power balance" display in a solar car.  It will
be subjected to vibration as well as high ambient temperatures. IIRC,
the moving coil meters don't typically like that sort of thing.

I'm not sure of all the options available to drive one to display the
quantities (PWM would depend on the mechanical response) ... and finding
one with a highly-visible needle is another task altogether.

Response time isn't that critical. As long as the full scale can be
traversed in about half a second or less, that's fast enough. I intend
to only show a moving average over one or two seconds anyway, otherwise
the display gets "too busy", causing the driver to make many adjustments
over time which aren't really necessary.

-- 
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