[amsat-bb] Re: Dish position pulse counter

[Phelps Williams]

Phil,

Have you identified the source of the noise?  However you regulate down the
5v for the pic, if you place a larger capacitor on the 5v regulated bus
(between 5v and gnd) this might help with these fluctuations, essentially
acting as a high pass filter.

If the power bus is clean, the noise might be induced along a long cable run
to the rotor itself.  It might be worthwhile to look at a differential a2d
with a spi or i2c interface.

Take a look at the Texas Instruments ADS1110.  It has an internal reference
voltage as well to help filter out these ratiometric effects.

Another option might be to switch over to a rs485 or rs422 link between the
rotor and your shack where the controller presumably is.

-Phelps
KI6GST


On Fri, Apr 25, 2008 at 6:29 AM, David Barber <
david.barber at dbelectronics.co.uk> wrote:

> If pulse counting is used and since presumably the duration and expected
> repetition of the pulse is known / can be calculated is it not possible to
> discriminate between noise and a valid pulse?
>
>
>
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of i8cvs
> Sent: 25 April 2008 11:11
> To: Phil; AMSAT-BB
> Subject: [amsat-bb] Re: Dish position pulse counter
>
> ----- Original Message -----
> From: "Phil" <phillor at telstra.com>
> To: <amsat-bb at amsat.org>
> Sent: Friday, April 25, 2008 1:46 AM
> Subject: [amsat-bb] Dish position pulse counter
>
> > Thank you for reading this.
> >
> >
> > I'm having second thoughts about the pulse counting scheme and I'm
> > beginning to think that the tried and proven ten-turn pot method might
> > be more fool proof.
> > Regards,
>
> > Phil.
>
> Hi Phil
>
> The ten-turn pot method is also not immune from inaccuracy when the
> voltage across the pot is close to 0 volt i.e. when the rotator is turned
> near to 0 degrees elevation.
> In this condition the noise voltage picked up by the cable running from
> the
> antenna to the control box can add with the low voltage available across
> the
> potentiometer.
> Since you are able to write a program for a PIC a better method to get in
> general a high pointing accuracy requested for a dish and expecially for a
> big dish is to use different type of position sensors like the following:
>
> Sequential encoders
> Absolute encoders
> Selsyn or Resolvers
>
> With two inexpensive surplus selsyn for the azimuth and two selsyn
> for the elevation on my dish I actually get a very accurate indication
> of position on mechanical pointers but adding the Analog Device chip
> AD2S80 I plan to write a program to get both precise digital indication
> and automatic tracking with high accuracy
>
> Look on google for the AD2S80 data sheet and for many technical
> applications of it with syncro-resolvers.
>
> Have fun
>
> 73" de
>
> i8CVS Domenico
>
>
>
>
>
>
>
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