----- Original Message ----- From: "Phil" phillor@telstra.com To: amsat-bb@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