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Homebrew Celestron-compatible GPS

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#26 ncolton

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Posted 27 August 2018 - 09:52 PM

Barry,

 

How did it go? Any luck? The link doesn't seem to be working anymore...

I found the same. I did get curious enough today and went hunting and found https://github.com/d...NexstarMountLib which looks rather promising. I can't say I understand it, yet, but the description is "Arduino Library to talk to the AUX port of Celestron Nexstar compatible mounts." and it definitely contains GPS interface.



#27 RogerClark

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Posted 05 November 2018 - 10:07 PM

I tried the link posted by Barry (https://github.com/bebrown/nexstar_gps)  but its now dead , in fact the whole bebrown account on GitHub is no longer there :-(



#28 Michael_Swanson

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Posted 05 November 2018 - 10:53 PM

Hi Roger,

 

Your NexStar GT mount and hand control aren't compatible with GPS input via the AUX (internal communications) bus as is being discussed here.

 

If you do get a version 4 hand control as I mentioned on the other discussion string, there are serial commands that can be sent via the port on the bottom of the hand control which allow you to set date/time/long/lat.

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com



#29 BarryBrown

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Posted 06 November 2018 - 12:17 AM

I tried the link posted by Barry (https://github.com/bebrown/nexstar_gps)  but its now dead , in fact the whole bebrown account on GitHub is no longer there :-(

I'm looking into it. Hope to get it resolved in the next few days.



#30 RogerClark

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Posted 06 November 2018 - 01:18 AM

Excellent.

 

Thanks.

 

I have an old Nexstar 4GT, and on the HC I've removed the old RS232 socket and also removed the voltage level translation IC, and I'm in the process of fitting a microcontroller connected to the serial connection to the Pic MCU.

 

My initial aim was to use a ESP8266 to provide serial over Wifi, but I found that my Nexstar serial commands are not compatible with most modern software e.g. Stellarium and Sky Safari etc.

So I'm going to get the ESP8266 to do command and response conversion.

 

But I could also get attach a GPS to the ESP8266 (or perhaps use a ESP32), so that I can get position and time from the GPS and send it to the HC.

 

Hence i was interested in your source code



#31 Michael_Swanson

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Posted 06 November 2018 - 01:31 AM

Roger,

Your GT version 101 hand control has, as you note, a small subset of the newer NexStar serial command set. There is no command that it recognizes which allows you to send time/location information to the HC. I haven't seen it, but I expect Barry's project is based on translating from an off-the shelf GPS module to the AUX command set found in the last link on this page (Andre Paquette's AUX Command Guide):
https://www.nexstars...mingNexStar.htm
or the pass-through command set found in the first link on that page (Celestron's NexStar Communication Protocol Documentation). The GT 101 HC simply doesn't understand those time/location commands.

Perhaps your next step should be a search for a version 4 hand control which does understand those commands. As the version 4 HC is no longer manufactured (replaced by the NexStar+ which is not compatible with your GT mount), one route might be to offer a newer scope owner (such as as an SLT, SE or CPC owner) a new NexStar+ HC in trade for their version 4 HC.

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com

Edited by Michael_Swanson, 06 November 2018 - 05:49 AM.


#32 RogerClark

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Posted 06 November 2018 - 04:09 AM

Mike

 

Thanks

 

I miss-read the commands doc and thought that the time and location commands were supported by my HC, but I agree that they are not supported :-(



#33 Gbaxendale

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Posted 15 November 2018 - 06:59 AM

Hi just wondered if you could share the link to the OEM unit you found?

Thank you
Gaz

Greetings,

I looked into replacement GPS units when mine had failed eight months into the warranty. I loathed the thought of packing up my scope and returning it to Celestron.

I eventually fixed my GPS unit myself (replaced $3.00 super-capacitor) but I was considering replacing the GPS module leading up to that.

I balked at the price of the Celestron replacement, I think it was $130, and I thought that they're making a killing on what probably is only worth 10's of dollars nowadays and that there was probably some standard unit that would work in it's place.

The old nexstar GPS 11 schematics and materials I found on the web talked about a motorola unit that uses a small lithium battery for backup and I looked at a lot of potential candidate replacements for the GPS module. But what they're using now is a GPS module made and designed in Taiwan that uses a super-capacitor for backup.

I don't know how compatible the communications protocols are between units. I know there's the standard NMEA, but I don't know for sure if or how they're using that. Then, there's that interface board between the GPS and the rest of the system. What is it doing and how is it affecting the communications? That's about where I lost interest in delving in deeper to the protocols.

I searched and found what I think is the identical unit from a Taiwan supplier but they're sold only to OEM's and cannot be bought singly. I got a quote for a sample order with a minimum quantity of five for $30 each. I would have bought one to try, but not five.

As an aside, when I was probing around on the serial bus for GPS communications between the GPS interface board, the GPS unit, and the rest of the system, I disconnected one of the serial connectors on the GPS interface board (I wanted to see which way the data was flowing). After that I got boot 008 messages from the hand controller and could not recover even after reconnecting the interface board!

It didn't surprise me that things stopped working when the interface board was disconnected, but it did surprise me that the hand controller didn't recover when communications was re-established!!! I thought I had toasted something.

I eventually recovered by re-flashing firmware on the HC but that's another story. Then I replaced the super capacitor and my GPS has worked well ever since.

I applaud your goal of learning more about how this works. Please keep us updated!


Edited by Gbaxendale, 15 November 2018 - 07:00 AM.


#34 colgs3b

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Posted 01 February 2019 - 09:17 AM

I’ve managed to get my Arduino Nano setup with a GPS receiver and a 128x32 OLED. I made a custom UI to show the position and time info. I verified that the Nano can be powered by the 12V line from my Advance VX mount’s AUX port (not shown).

EFFFD24B-310B-4793-BEF3-EB1D0A1A20E9.jpeg

Of note, relatively few of the more recent small microcontrollers can take 12V input, so if you plan to try this out, pay attention to the specs. The Nano works. The 5V version of the Adafruit ItsyBitsy 32u4 is supposed to be able to take up to 16V input, so it might be a candidate, but I haven’t tested it.

 

To do:figure out communication and wiring for the AUX port. I have a RJ12 jack all set. Paquette’s document gives pin info. I’ll have to learn about RTS/CTS. The data lines are showing 5V on them, so I don’t know if I’ll need to put an optoisolator in between for some protection.


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#35 MiroM

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Posted 08 February 2019 - 03:07 PM

I'm posting everything on GitHub:

 

https://github.com/bebrown/nexstar_gps

Thank you very much for this great work! As proud smile.gif AVX mount owner I was looking for some alternative GPS device. Original SkySync GPS is very expensive here in Europe (around 250 euros). And then I found your project and my old hobby in micro-controlers. wink.gif  

Here is my fork: https://github.com/F...ree/nexstar_gps.

This library also supports GPS_GET_LAT/GPS_GET_LONG commands and was successfully tested on my AVX mount.

 

Miro



#36 MiroM

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Posted 08 February 2019 - 03:16 PM

I’ve managed to get my Arduino Nano setup with a GPS receiver and a 128x32 OLED. I made a custom UI to show the position and time info. I verified that the Nano can be powered by the 12V line from my Advance VX mount’s AUX port (not shown).

attachicon.gif EFFFD24B-310B-4793-BEF3-EB1D0A1A20E9.jpeg

Of note, relatively few of the more recent small microcontrollers can take 12V input, so if you plan to try this out, pay attention to the specs. The Nano works. The 5V version of the Adafruit ItsyBitsy 32u4 is supposed to be able to take up to 16V input, so it might be a candidate, but I haven’t tested it.

 

To do:figure out communication and wiring for the AUX port. I have a RJ12 jack all set. Paquette’s document gives pin info. I’ll have to learn about RTS/CTS. The data lines are showing 5V on them, so I don’t know if I’ll need to put an optoisolator in between for some protection.

Hello, I just finalise my project of GPS receiver for AVX. Maybe this can help you: https://github.com/F...ree/nexstar_gps.

 

Miro


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#37 colgs3b

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Posted 09 March 2019 - 04:42 PM

Miro's work really helped me out, especially the schematic.  I had to make a few minor modifications since I was using an Arduino Nano, and I had that OLED also attached.  I soldered up a circuit board and 3d printed up a case.  Inside it takes a little while to acquire the satellites, but outside isn't a problem.  After I took the below picture, I covered the OLED screen with a red transparent film so that it doesn't affect night vision.  IMG_0142.jpg

I know I can make it all smaller if I want to design a real circuit board.  Right now, all the modules (Arduino, OLED, GPS, RJ12 breakout) are attached with headers so that I can remove them if needed.  At some point I'll get around to making a branch and uploading my code.

 

Thanks Miro!


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#38 MiroM

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Posted 19 March 2019 - 10:10 AM

Great job Jeff. Very nice 3D-printed box waytogo.gif  .

This is my final solution:

PCB designed in Eagle and purchased at https://jlcpcb.com/. Universal box bought in local store and non-removable RJ11 cable.

Only one red LED for minimalistic state signalisation (error = fast blinking, waiting for fix = slow blinking, GPS fixed = no blinking).

 

IMG_20190319_151221.jpg

IMG_20190319_151644.jpg


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#39 colgs3b

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Posted 19 March 2019 - 07:33 PM

I like it Miro!
I started learning a bit about designing PCBs in Eagle, and maybe someday I’ll get around to making a pretty board.
I got outside last night with mine (finally clear skies), and setup was a breeze with quickly acquired GPS coordinates and time.
Cheers.
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#40 TheBum

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Posted 14 April 2019 - 10:58 PM

I forked Miro's repo and added SSD1306 128x32 OLED display support. It's similar to colgs3b's implementation with the addition of GPS fix status, which eliminates the need for the LED. My fork is here:

 

https://github.com/TheBum/nexstar_gps

 

IMG_0204.jpg

IMG_0207.jpg

IMG_0213.jpg


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#41 Noah4x4

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Posted 14 April 2019 - 11:37 PM

Nice, fun DIY project, but SkySafari for IOS/Android or CPWI for PC/Windows now renders GPS unnecessary for Celestron owners where there is an Internet connection or G3/G4 so a mobile phone can be used as a hot spot.. Since embracing CPWI my SkySync GPS accessory has become redundant. 



#42 TheBum

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Posted 15 April 2019 - 11:07 PM

There are places in the US without cell coverage, like where my mother-in-law lives. Also, I want to be able to set up and align with StarSense without pulling out my phone. The total cost comes to less than $50 and it's a more capable unit than Celestron's, so it's a worthwhile project IMO.



#43 colgs3b

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Posted 16 April 2019 - 07:14 AM

TheBum, you stole my thunder by getting it into github first. ;)
1) Fun project
2) Inexpensive (ok, you need a soldering iron)
3) Doesn’t require an internet connection

The SkyPortal WiFi dongle is $100. Or you can go cheaper and use a Raspberry Pi with a little configuration of serial communication and access point setup so that it can talk to SkySafari. BTDT. SkySafari still needs a way to get GPS coordinates. Cellular GPRS will take a little longer out in the middle of nowhere.

Anyhow...

#44 TheBum

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Posted 17 April 2019 - 08:45 PM

TheBum, you stole my thunder by getting it into github first. wink.gif

You had nearly a month to get it done. tongue2.gif

 

I added my EAGLE files for my Nano implementation plus a zip file of all the files needed to order a circuit board.



#45 Philip J. Fry

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Posted 19 April 2019 - 10:49 PM

Excellent work, Miro!

 

Barry, thanks for fixing the link!



#46 astronate

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Posted 14 May 2019 - 05:29 PM

Thanks Barry, Colgs3b, Miro,and TheBum for figuring this out.

 

This looks like a fun project so I thought I'd try it.

 

I wired up TheBum's schematics (I tried colgs3b too) and I was able to get the position and time on the oled display and also sent to the handset of my 6SE with a GPS Linked message.  However,  I did get a message saying "No Response 16" and "No Response 17".  Luckily, those messages went away when I disconnected the GPS and power cycled the mount so I don't think I did any damage.  I realized before I started that I'm proceeding at my own risk.

 

I was wondering if any of you had seen that error when you were working your projects?  Do you have any suggestions on how I might troubleshoot?

 

Thanks,

Nathan 


Edited by astronate, 14 May 2019 - 05:33 PM.


#47 Lord Beowulf

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Posted 14 May 2019 - 10:55 PM

Since 16 and 17 are the motor controllers and the error means the HC couldn't communicate with them, I'd suspect a problem on the shared serial port.  You have to operate open collector so that any device can drive the shared communication line.  If your module isn't doing that properly, then nothing else will communicate either and thus the communication errors when the HC tries to initialize.

 

Beo


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#48 ProstetnikJeltz

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Posted 13 June 2019 - 09:37 AM

Hi,

 

I'm new to this forum because I was curious about the "Celestron GPS thingie" getting to work.

I'm from the surroundings of Munich, Freising, which is 30km away from Munich (but we have the Munich airport nearby).

 

I have a little problem, getting the ublox neo6 communicating.

It works fine with the ublox suite, attached by an USB-TTL converter set to 9600 8N1.

As soon as I hook it on the Ardunio (nano), the display says (you see, I used the sw from TheBum ;) ) **NO DATA** .

Maybe the neo is wrong configurated.

The messages sent from neo are UBLOX and NMEA, should I switch to NMEA only?

The other thing I was confused, that the communication to the scope runs with 19200 8N2 (is the 2 correct and shouldn't it be 9600 bauds?).

 

You don't have to answer the questions when the answers are "hidden" in the files mentioned in the "README.md".

But if so, please let me know, because by now, I didn't find the answers.

The problem is, that I'm rather a "maker" than a "programmer".

I'm etching PCBs, do the Layout, solder down to 0,5mm pitch and so on ... .

I'm able to read the ino and most of the time I understand, what should happen, but I've never written any piece of sw, which worked  - despite of blinking and hello world and some BASIC on the ZX81 and C64 ;) .

So please forgive me my maybe stupid questions smile.gif .

 

Greetings from Munich

Uli



#49 colgs3b

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Posted 14 June 2019 - 08:43 PM

No Data suggests that you might have the wiring wrong. Can you post a picture?

#50 cmku

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Posted 31 October 2019 - 03:27 PM

Great work Gentelmans.

I make this project and gps module, oled is working fine, i have gps  position etc but cant connect to my AVX it says "no gps found"
I connect serial pin from my arduino to green serial in my AVX is this correct ? Status led is blinking when im trying to turn on gps in my hand controller, it looks like it communicate with arduino in only one way. Is this black serial pin should be connected  somewhere ?
 

IMG_5661.JPG

 

My setup is the same like this, so serial pin 2 is is between 12v and GND.
 

Nano-schematic.jpg




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