Last updated: 13 May 2001

Notes on the 909 Accessory Port/Peripheral Module for LX90's

From:	rseymour@wolfenet.com (richard seymour)
In the LX90 Egroup, Janet asked:

> They sure don't give much information about the autoguider port
> do they? I was hoping that they would at least list compatible
> guiders, or the pinouts of the connector.

It's exactly the same as the LX200's CCD guider port.
Since Meade's descriptor of -that- is beyond confusion into
   befuddlement, here's my go at it:

Looking into the hole on the 909APM, the pinnage is:
               | 1 2 3 4 5 6 | 
               +----+   +----+

1  "NC contact" (not used)(many CCD guiders apply +5v here)
2 - Ground
3 - Left (CCW)
4 - Down
5 - Up
6 - Right (CW)

 All signals are pulled low (to ground) to assert.
 So i have become a "wetware CCD" with 4 pushbuttons...
They each can tie the pin-2 Ground to any of the pins 3 thru 6 inputs.
    My megapixel eyeball provides the pushing power.
The scope ignores confusing (go left/right simultaneously) inputs.
[GoTo] and manual slewing override the CCD input.
   It only works in Polar.  (Why?)

The APM also has a Focuser and Reticle connector which i think are
specific for the Meade accessories.    I don't have them, Clay does.
> I assume you have the APM. Would you mind answering a few questions?
>  What are your impressions as far as it's quality and use?
It's a decent lump.  Many components inside.  Cute mounting.
Lacks any external indication of CCD operation. No LEDs.

>  Is the cable long enough?
The cable is a thinner-guage, but a coil cord the same length as
my ETX90's Autostar cable. (stretchable to 3 feet, easily)
Plugs into the AUX port on the telescope base.

> Does it interfere with your access to the focuser, or the visual
> back?
A little plastic clip screws onto a fitting just below your rear port.
The 909APM itself slips onto that, and can be easily removed.
It does not -have- to mechanically attach to the scope to work.

>  Have you used a CCD guider with it yet?
 I haven't, but i've pushed its buttons...

Result: the Guide speed it commands seems to be about -half- of
"speed one" on the Autostar.  Whereas speed one is "1x sidereal",
and pressing the Autostar's anti-sidereal slew key effectively stops
the RA drive, pressing the "retard" button (mimicing the CCD) only
slows it down. The motor does not go silent.
Up/Down (Dec) shows stars slowly entering/exiting the edge of the FOV.
I haven't had time yet to time how long it takes to fully cross a 
measured visual field.

The CCD guiding function uses your backlash percentage settings to give
the motors a start-up kick if it reverses them.
Since it only slows, and doesn't actually -reverse- the sidereal motor,
you won't see it in RA motion.  But you -will- see it in Dec motion,
so you'll have to ensure that your values are correct, or, if anything, 
under-correct for the backlash.

I ran a long-term test with the 909 APM, commanding a continual
Upward correction.  It appears to move at about a 10 arcminute per
clock minute rate.  That's 2/3rds sidereal rate.  

(the 2/3rds sidereal is the **CCD** guide speed effect.
Measured in a DEC direction (elevating barrel), with continual
 input on the "up" CCD pin.
Not normal operational tracking.)


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Copyright ©1999-2001 Michael L. Weasner / etx@me.com
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URL = http://www.weasner.com/etx/autostar/as_apm.html