EME Controller OE5JFL May 2009
Page 5 of 13
Encoder Input:
It is possible to connect 10bit, 11bit and 12bit binary encoders
with 0.5deg, 0.2deg, 0.1deg resolution and 12bit Graycode encoders
with the widely used SSI-protocol. To prevent the controller inputs
from damage, there are switching transistor stages for each clock
output and data input. You have to set the 4 jumpers JP1..JP4 at
the transistors, but must let the RS485 sockets without the ICs.
You can also connect the well known A2-S-S encoders from US-digital
via RS485. In that case the SEI-protocol is used and you have to
unplug the four jumpers JP1..JP4 on the board and instead plug the
two RS485 drivers into the sockets.
I developed an easy to build 0.5deg 10bit encoder, which fits
nicely to the controller. But meanwhile a cheap 12bit encoder is
available, the ETS25 (mechanically improved replacement of the
discontinued MAB25). It´s accuracy is worse compared to the A2-S-S,
but first measurements showed a maximum deviation of only 0.2deg.
DF1SR offers encoders similar to the ETS25, named HH12 and HH16.
The HH16 has 16 bits, but only 12 bits can be used by the system,
and you need special firmware for using it. He also offers an
Inclinometer HH12-INC, electrically the same as the HH12.
Occasionally there was an unstable indication with the MAB25,
probably because of pulse reflections. Adding 1k resistors from
each encoder pin (CLK,DATA,CS) to GND directly at the encoder or at
the splitter board cured the problem.
Different encoders will need an updated firmware and maybe a
modified hardware connection.
If you want reversed indication direction of azimuth (for example
if the axis of the encoder is looking downwards), connect
pin2(center) and pin3(right) of SL2 (placed in front of CON1) by
setting a jumper. The 0…360deg of the elevation encoder is
converted to -90…0…+90…0…-90. So if the indication is in the wrong
direction, just turn the mounting of the encoder by 180deg.
You can teach the system to compensate a not correct mounting of
the encoders. Point the antenna exactly at a target with well
defined position, for example the sun. Connecting pin1 and pin3 of
SL2 for five seconds (P3.3 of the controller grounded) will store
the indicated target position into antenna position, and always
take the difference to the encoder position into account from that
moment. Connecting the two pins for a short moment only, will
toggle the system between normal indication and compensation mode.
The teaching and toggle functions are provided as well as remote
commands via the COM port. See details about that on page 13.
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