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Add DIY-GPS to Nexstar SLT

Accessories Celestron DIY
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#1 vidalv

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Posted 05 July 2022 - 12:46 PM

Hello All !
I don't know if it's the right place for this subject? The admin can move it if it's not good, please.

So, I want to add a GPS to my NEXSTART SLT.

I know that Celestron sell one, but I would like to create my one using a GPS module available in the Arduino world.

On my mount there is a free port AUX on which I connected a SkyPortal module to communicate with my PC in WiFi, the other port being used by the HC.

On the HC bottom there is a 4-pin connector RS-232.

My question: can I connect a GPS system to wearing HC?

The RJ9 4P4C diagrams gives three pins, the ground, a TX and RX signal.

I don't know if there is 12V available?

There are many subjects already discussed but without real diagrams or connection via the RS-232 port.

Another solution is to duplicate the AUX port on the MC of the mount (here also this Celestron selling a Splitter) but I suppose that we must just duplicate the 6 signals of the AUX to create an AUX2?

Ideally I would use a BN-220 GPS module or a GY-GPS6MV2 all connected to an Arduino Mini Pro in 5V.
As the mount is powered by 12V a regulator will provide the 5V from it.

 

I've made a Kicad schematic from base of Mark Lord idea.

 

Thanks for any ideas and suggestion.

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#2 mlord

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Posted 05 July 2022 - 02:03 PM

The RS-232 port is NOT suitable for a GPS connection.  So instead use an AUX port.

And do not use a 7805 linear voltage regulator:  they get much too hot and waste power.

 

Instead, use a DC-to-DC Buck Converter module, which is like a mini switching power supply.

Much better.

 

Cheers



#3 vidalv

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Posted 05 July 2022 - 11:58 PM

Thank you Mark for this good remark, I did not take into account the dissipation of heat, with a voltage drop of 7V and the current variation of the Arduino and the GPS module it can make several watts!

Regards.



#4 vidalv

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Posted 06 July 2022 - 09:42 AM

Hi Mark, BTW do I need to buffer individually each RJ45 or I can connect it in parallel directly?

I mean can I use a "Y cable" or "splitter"?

RJ45-1X3.jpg


Edited by vidalv, 06 July 2022 - 09:55 AM.


#5 mlord

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Posted 06 July 2022 - 02:02 PM

The aux ports (and hand-controller port) are all identically wired in parallel.  Each pin on each port is directly wired to the corresponding pins on every other port.  No buffering.

 

I cannot vouch for the splitter pictured above -- I don't know how it is wired.

 

Cheers



#6 vidalv

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Posted 06 July 2022 - 02:06 PM

Thanks Mark, I'll ask to check before order ! Thanks.


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#7 vidalv

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Posted 07 July 2022 - 02:35 AM

Thanks to @tjay for the link,

but I'm not sure the need to add Pull-Up resistors (R1, R2 and R3), on Arduino they are included (but need to be activated) question.gif

 

AUX1-AUX2.jpg

 



#8 vidalv

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Posted 09 July 2022 - 05:11 AM

Hi there,
So, after reflection, it seems that I am wrong with regard to the Y cable, it is not an RJ12 but RJ45 (RJ12 is 6 wires and RJ45 is 8).

From another point of view, do I need a GPS module when using the SkyPortal Dongle?

Let me explain, the SkyPortal allows me to make a WiFi connection between a PC or a smartphone and my mount.

With my smartphone if I use the SkyPortal Application, I must be able to recover the position of the smartphone and send it to the mount right?

If someone has an experience or a tutorial on the subject I am information taker. Thanks!



#9 crn3371

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Posted 09 July 2022 - 03:12 PM

The first thing that came to my mind when I saw your post was why? If controlling via WiFi using an app like SkyPortal, or SkySafari, the scope will draw correct time and gps coordinates from the app. I’d think that in most cases a separate gps module would be superfluous.



#10 vidalv

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Posted 10 July 2022 - 03:58 AM

Hello and thanks @crn3371, you're right, no need to use an external GPS with the Skyportal.

I need just to understand how to setup correctly my HC (the old one not the NextStar +) to collect the right infos from Skyportal software.

BTW is there somewhere I can find the Skyportal RJ12 Pinout ?

Or is the same as from CG5 :

Celestron-CG5-AUX-Pinout.jpg

Thanks.

 



#11 crn3371

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Posted 10 July 2022 - 09:34 AM

If using the hand control you manually enter gps coordinates. If using SkyPortal it automatically takes gps coordinates from your phone or tablet and inserts them into the app. You can only use one device at a time for alignment and goto’s, you can’t align with SkyPortal and then use HC for goto’s. 



#12 Zoroastro

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Posted 10 July 2022 - 04:30 PM

The first question that came to my mind was "why aren't you building the DIY HomeBrew GPS/Bluetooth/WiFi module designed by @mlord?".

 

We built dozens of it and works flawlessly on my Celestron.



#13 mlord

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Posted 11 July 2022 - 05:37 PM

Hello and thanks @crn3371, you're right, no need to use an external GPS with the Skyportal.

I need just to understand how to setup correctly my HC (the old one not the NextStar +) to collect the right infos from Skyportal software.

That's easy:  YOU DON'T !!!

 

The SkyPortal app, or SkySafari, or CPWI, are all "controllers", which REPLACE the hand-controller. Only the "active" controller needs GPS time/location info, and if you are using an app it normally gets all of that automatically from the smart-device the app is running on.  The hand-controller simply isn't involved, unless you want to use it as a dumb slew-only device.




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