Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

EO Pro and Garmin 18x-LVC for millisecond time accuracy

Solar Software Eclipse
5 replies to this topic

#1 chakel

chakel

    Mariner 2

  • *****
  • topic starter
  • Posts: 288
  • Joined: 25 Jul 2017
  • Loc: No. AZ

Posted 24 January 2024 - 02:07 PM

Has anyone tried to wire up a Garmin 18x-LVC to a DB-9 connector along with a 5V source per the wiring diagram in the manual to take advantage of the pulse-per-second signal to provide a very accurate time source?

 

If so, has it impacted your past use of EO Pro in the field?

 

Thanks in advance for your replies,

John

 

 

 



#2 jnmyersnj

jnmyersnj

    Lift Off

  • -----
  • Posts: 12
  • Joined: 13 Aug 2017

Posted 26 January 2024 - 07:05 PM

I used that exact setup in 2017, with EO Pro and the 18x-LVC.  It worked perfectly.  At the moment, I'm struggling with it a bit trying to prep for this April.

I must be doing something incorrectly, as I know the unit is sending the signals, both the GPS "words" and the 1 pps pulse (I can see it on an oscilloscope).

I use a 9V "transistor" battery (like for a smoke alarm) supplying 5 V to the Garmin unit via a 7805.  It's not that hard to do if you are comfortable soldering.

So, I'd say it is worth a try.

I have found EO a bit balky and the consensus is that it is more important to get your shutter running quickly, e.g., with a separate shutter release.

There are a bunch of EO threads going, I'm jumping around a bit looking for advice too.  

Jeff M



#3 chakel

chakel

    Mariner 2

  • *****
  • topic starter
  • Posts: 288
  • Joined: 25 Jul 2017
  • Loc: No. AZ

Posted 26 January 2024 - 11:08 PM

Jeff, 

With the 18x LVC, I assume you followed the wiring diagram presented in the manual. If so, did you also use a USB to Serial (DB-9) converter cable to connect the GPS to your laptop?

CS,

John



#4 jnmyersnj

jnmyersnj

    Lift Off

  • -----
  • Posts: 12
  • Joined: 13 Aug 2017

Posted 28 January 2024 - 12:23 AM

Hi John, yes, I did follow the wiring diagram, and I am using a USB to serial DB-9 (broadcom).  On the setup software SNSRXCFG, I get a nice clock output and the GPS NMEA words coming in on the terminal window.

So I know the unit is talking to the computer.  I will be working on this again tomorrow (Sunday).

 

I see on the oscilloscope some signal crosstalk on the pulse line, i.e., there looks to be some GPS signal (low level but clearly not just noise) coming through on the line that provides the 1 pps pulse.

And the low-level signal on the pulse line is completely in synch with the GPS output, which I can tell because I am monitoring it with another channel at the same time.

I may have to put in some capacitance from the pulse line to ground to knock this down.  That could be an issue, I'm not sure.

 

My main concern is the shutter - I checked the wiring, it seems correct, and also with the correct signal (RTS to PNP base etc).  I tried switching to a longer pulse, 150 ms.  Now it is firing, but I must not be giving it enough delay, because it misses a lot of the short exposures while it is writing to the memory card.  Also, when I plug everything in and turn on the camera, the shutter runs nearly continuously until EO is up and running. Is that normal? 

The EO documentation is basically useless.

 

Thanks,
Jeff



#5 jnmyersnj

jnmyersnj

    Lift Off

  • -----
  • Posts: 12
  • Joined: 13 Aug 2017

Posted 29 January 2024 - 12:14 AM

Nikon RS232 shutter switch.png Well, here is a good one:  The Prolific USB to RS232 cable (DB9) sets RTS to "ON" when it first turns on.  That is, because in RS232, "ON" means a negative voltage level (yes, that's correct), this pin reads -7 V relative to pin 5 ground.  So that's why my shutter goes crazy when i plug this in.  Now, there is a check box in the Advanced port settings, that says "Change DTR/RTS INIT Level Shift (from TTL=HIGH/RS232=LOW to TTL=LOW/RS232=HIGH), and when I do that, it switches RTS (pin 7) and DTR (pin 4) so that they now read +7 V relative to the pin 5 ground.  I will see tomorrow if this fixes my problem on my laptop; I did this on a different computer.

The challenge will be if this is the initial state, will EO be smart enough control the port properly.  I hope so, since the box in the Advanced settings says "INIT level shift" so I hope it's just initializing it.  

For fun, I drew the DB9 circuit that the Nikon cable connects to, using circuit-diagram.org (attached).  the "ground" is not real, i.e., unless the USB cable ground is a real ground.  I just added that for what i hoped would be clarity.



#6 Tech Hiker

Tech Hiker

    Vostok 1

  • -----
  • Posts: 167
  • Joined: 29 Jul 2009
  • Loc: Columbus Nebraska USA

Posted 04 February 2024 - 11:18 AM

I'm not sure I like that circuit.  That is going to pull the shutter and focus camera inputs below "ground".  Your camera may not like that.

 

This is the circuit I used.

 

Attached Thumbnails

  • SerialCableOpto.jpg




Reply to this topic



  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Solar, Software, Eclipse



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics