[amsat-bb] magnetic reed switches for indication

Robert C. Campbell kb3pmr at gmail.com
Fri Aug 9 03:00:43 PDT 2013

I am using reed switches for both my AZ and EL visual feed back on my
newest build. I have had to slow the motors down with a PWM so that the
reeds don't skip a count. Both AZ and EL are still within the speed of
keeping up with ISS. You can determine the ratio of motor turns to one
revolution of the AZ  full 360 or 90/180 for the EL and use that ratio to
determine the position in degrees. Repeat-ability seems very good. If you
are going visual/manual positioning you can check on utube or
instructables.com and find a easy build for a modified  $ 2.00 Dollar
General calculator that then becomes a pulse counter by simply connecting
the enter button to your reed and entering the ratio and pressing the plus
sign. Then each rotation the calculator will tell you the degrees the
antenna is looking at. Yes, it does need reset after each pass, and yes, if
you run by the bird and go back the calculator will give you some extra
counts since it is counting reed switch contacts not true degrees of
indication. Purchase 5 of them, one for practice, 2 for EL and 2 for AL
then if you start from the same standard position each time one can add and
one can subtract. This should work fine assuming that the driver maintains
mental focus. It is a small fun project and cheaper then happy hour at the
local pub. The Pulse Width Modulator works good with this because you can
adjust the speed of the motors to keep up with the bird. This of course
assumes you are working with direct current motors.


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