O/T Digital Position sensing

[Keith Goggin]

Could anyone recommend some light reading on Digital Position Sensing?


I need to know the position of a shaft that can rotate through about 90
Degrees. I have tried a rather crude setup with a micro-switch but I
require something a little more sophisticated.
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[Adam Thomas-5]

Read up on grey codes and optical encoders.

On 11/3/09, Keith Goggin <keith.goggin@...> wrote:

> Could anyone recommend some light reading on Digital Position Sensing?
>
>
> I need to know the position of a shaft that can rotate through about 90
> Degrees. I have tried a rather crude setup with a micro-switch but I
> require something a little more sophisticated.
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> linux@...
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>

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[Brett Worth-2]

Keith Goggin wrote:
> I need to know the position of a shaft that can rotate through about 90
> Degrees.

What sort of resolution do you need?

Brett
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[Ben Coughlan]

You could try something like a http://reprap.org/bin/view/Main/Magnetic_Rotary_Encoder_1_0 
.  The linked product doesn't seem to be available anymore, but the  
concept is certainly more sophisticated.

Ben

On 03/11/2009, at 11:11 AM, Keith Goggin wrote:

> Could anyone recommend some light reading on Digital Position Sensing?
>
>
> I need to know the position of a shaft that can rotate through about  
> 90 Degrees. I have tried a rather crude setup with a micro-switch  
> but I require something a little more sophisticated.
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> linux@...
> https://lists.samba.org/mailman/listinfo/linux

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[Ben Nizette-2]

On Tue, 2009-11-03 at 11:11 +1100, Keith Goggin wrote:
> Could anyone recommend some light reading on Digital Position Sensing?
>
>
> I need to know the position of a shaft that can rotate through about 90
> Degrees. I have tried a rather crude setup with a micro-switch but I
> require something a little more sophisticated.

As mentioned elsewhere, optical encoders give you good resolution but
it's only a velocity thing.  You can integrate it to position but there
is then the probability of accumulated error if/when you miss readings.
The /simplest/ thing for absolute position I can think of given the
limited range is a potentiometer and ADC.

Do you have any other criteria regarding resolution, speed, mechanical
specs, acceptable load added to the shaft etc?  What are you using to
get this data out (pc, microcontroller etc)

        --Ben.

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[David Tulloh-2]

Ben Nizette wrote:
> On Tue, 2009-11-03 at 11:11 +1100, Keith Goggin wrote:
>  
>> I need to know the position of a shaft ...
> The /simplest/ thing for absolute position I can think of given the
> limited range is a potentiometer and ADC.
They come packaged together and are generally referred to as encoders.

Farnell sells them from $10,
http://au.farnell.com/absolute

Incremental (relative) encoders are much cheaper and start from $1.50.
http://au.farnell.com/incremental

I would recommend one of those over hacking up a mouse.  You get a
better end result with known specs for only a few bucks.


David
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[Alastair D'Silva-3]

> -----Original Message-----
> From: linux-bounces@... [mailto:linux-
> bounces@...] On Behalf Of Keith Goggin
> Sent: Tuesday, 3 November 2009 11:12 AM
> To: linux@...
> Subject: [clug] O/T Digital Position sensing
>
> Could anyone recommend some light reading on Digital Position Sensing?
>
>
> I need to know the position of a shaft that can rotate through about 90
> Degrees. I have tried a rather crude setup with a micro-switch but I
> require something a little more sophisticated.

One simple method that I have seen used in measuring propeller shafts, as
well as throttles for electric bikes is to epoxy a small neodymium magnet
onto the shaft. You can then read the position of the shaft via a Hall
effect sensor adjacent to it.

Cheers,

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[Keith Goggin]

David Tulloh wrote:

> Ben Nizette wrote:
>> On Tue, 2009-11-03 at 11:11 +1100, Keith Goggin wrote:
>>  
>>> I need to know the position of a shaft ...
>> The /simplest/ thing for absolute position I can think of given the
>> limited range is a potentiometer and ADC.
> They come packaged together and are generally referred to as encoders.
>
> Farnell sells them from $10,
> http://au.farnell.com/absolute
>
> Incremental (relative) encoders are much cheaper and start from $1.50.
> http://au.farnell.com/incremental
>
> I would recommend one of those over hacking up a mouse.  You get a
> better end result with known specs for only a few bucks.

Ok Thanks all, I've got a bit of reading to go on with. I particularly
liked Andrew's "Good Use of Technology"

Responding to the various requests for more detail, my project is to
monitor a throttle shaft setting in an automotive environment. The arc
of rotation is about 90 Degrees. The accuracy required is about +/- 2
Degrees.

Initially I only need to identify two points in the range of throttle
settings but provision for more would be useful.

My initial attempt involved a cam/micro-switch setup but I found engine
vibration made this impractical.

I see Jaycar Electronics have Hall Effect Kits so next time I'm in
Fyshwick I'll have a look.

Thanks again

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[Alastair D'Silva]

> -----Original Message-----
> From: linux-bounces@... [mailto:linux-
> bounces@...] On Behalf Of Keith Goggin
> Sent: Thursday, 5 November 2009 6:24 PM
> To: linux@...
> Subject: Re: [clug] O/T Digital Position sensing
>
> Responding to the various requests for more detail, my project is to
> monitor a throttle shaft setting in an automotive environment. The arc
> of rotation is about 90 Degrees. The accuracy required is about +/- 2
> Degrees.

You may also be able to get this information off the OBDII if your engine
has a recentish ECU.

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