#1  
Old 29-12-2010, 11:48 AM
alistairsam's Avatar
alistairsam
Registered User

alistairsam is offline
 
Join Date: Nov 2009
Location: Box Hill North, Vic
Posts: 1,815
Guide Camera signalling

Hi,
would anyone know details of how guide camera signalling works?
I'm guessing ST4 and LX200 protocols are sort of standards from respective manufacturers, I'm trying to understand how correction pulses are framed from guide cameras so I can interface it to my microcontroller based stepper drive for tracking.

to explain further, I've built an mcu based stepper controller for a home built fork mount, and i'd like to add an autoguider so I can send correction pulses to dec and ra motors to compensate for drift.

i've come across the pinouts for the guide cameras, dec-, dec+, ra-, ra+, but needed to know how the signals are sent, their pulse widths, etc.

are they pulses, do they use pwm?

thanks.
Reply With Quote
  #2  
Old 29-12-2010, 03:39 PM
RickS's Avatar
RickS (Rick)
PI cult recruiter

RickS is offline
 
Join Date: Apr 2010
Location: Brisbane
Posts: 10,582
Quote:
Originally Posted by alistairsam View Post
Hi,
are they pulses, do they use pwm?
I think they are just simple on/off signals. Take a look at some of the material at http://www.store.shoestringastronomy...roducts_gp.htm.

Cheers,
Rick.
Reply With Quote
  #3  
Old 29-12-2010, 04:42 PM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,312
All ST4 does is supply an earth pulse on either Ra+. Ra-..etc etc.

In the early days...this "earth" switched a relay coil which in turn supplied pwr to drive a motor etc.

Generally nowadays it is used to switch a opto diode or even the emitter of an NPN transistor..or base of a PNP transistor.

In this pic the ST4 command (from Rj11 pin 6..from the autoguider) is an earth pulse to a opto diode...that drives a phototransistor.

In other words..the autoguider outputs an earth pulse (as appropriate commanded by guide software, either Ra+ or so on) which is used to command a drive motor system to move.

Hope this helps.
Reply With Quote
  #4  
Old 29-12-2010, 08:59 PM
alistairsam's Avatar
alistairsam
Registered User

alistairsam is offline
 
Join Date: Nov 2009
Location: Box Hill North, Vic
Posts: 1,815
Quote:
Originally Posted by wasyoungonce View Post
All ST4 does is supply an earth pulse on either Ra+. Ra-..etc etc.

In other words..the autoguider outputs an earth pulse (as appropriate commanded by guide software, either Ra+ or so on) which is used to command a drive motor system to move.

Hope this helps.
Hi,

Thanks. So an autoguider input on the mount is active low?

I'm looking to take autoguide signals from a guide camera's st4 port like the orion starshoot autoguider. of the 6 pins, are the 4 pins (ra,dec) held high till a correction is required, and then the respective pin pulsed low?
would you have pinouts of a guide camera?
how different is lx200 or the lx200 protocol or is it not related?
Reply With Quote
  #5  
Old 30-12-2010, 09:18 AM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,312
Yes an auto-guider output to the mount is a "low". I tested my old Gotostar by shorting from earth to one of the guide inputs and could see the appropriate command like "Ra+" appear on my LCD screen. Don't know if other mounts can display this?

Most guide cameras have an RJ11, 6 pin...and unfortunately the configuration of these pins is and can be different between mfgrs and designers see here (for the most common config) and here for an alternate and there are lots.

Lx200 protocol is a set of serial command instructions (written long long ago that became a Pseudo standard) that is usually used in ASCOM to control a scope mount. It has things like Mw (move west), Me (move east), Ms, (move south), Qn (quit north), Qe (quit east)...you get the idea.

So you can hook up your mount to your computer and control the mount as long as it conforms to the command set. You can hook up your computer to mount via serial and use hyper terminal to see how it responds with the above commands.

Hope this helps.
Reply With Quote
  #6  
Old 30-12-2010, 11:05 AM
alistairsam's Avatar
alistairsam
Registered User

alistairsam is offline
 
Join Date: Nov 2009
Location: Box Hill North, Vic
Posts: 1,815
Thanks for that. will have to get hold of a guide camera and test the signals on an o'scope.
as for guide cameras, which one would be the most basic model that comes with a guide port?
i'm guessing its usb port will be used to preview the image on a PC?
Reply With Quote
  #7  
Old 30-12-2010, 11:30 AM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,312
USB port is for viewing and controlling guide camera with software like PHD...on a laptop.

The guide software determines any guide error and sends a correction back to the guide camera (via USB) which then outputs the appropriate Ra+. Ra-..etc earth pulse to the mounts ST4 (RJ11). PHD auto-calibrates and thus it can determine which way is N/S/E/W...no need to worry which way you put in the guide camera. This will cost around $350Aust.

That's generally how most "cheap" auto-guiders work.

However...the original ST4 was a standalone guider with a control panel that didn't need a laptop nor guide software. The same with the newer SG4 guider but this doesn't even need a control panel...it's just the head unit.

But...these stand alone solutions are more expensive (around $1800 Aust for the SG4) and I guess most people figure if they are imaging then you'll need a laptop in any case.

A cheaper guiding solution is "pulse guide". In this you use something like a web-cam as a camera (aka a Philips SPC900NC, $90 Aust) which plugs in via USB.

Again you use PHD but this time you select ASCOM pulse guide..that is you control the mount via ascom (either serial control or USB control..or whatever to your mount) and PHD adds drive "pulses" to make the mount move faster or slower in the desired direction (correcting for guiding errors). This works very well and is a lot cheaper. But of course..you must be able to control your mount via ASCOM!

All this said...I think most people like the simplicity of a guide camera and ST4...well I do.

Hope this is not too long winded!..more reading here by Craig Stark.

edit:
You can get USB to ST4 converters to use web-cams as an ST4. There are also a new generation of cheap standalone guide camera out nowdays. Meh!...not my cup of tea..although the TV guider is a treat. A few IIS'ers use this one was for sale recently!

Last edited by wasyoungonce; 30-12-2010 at 11:47 AM.
Reply With Quote
  #8  
Old 30-12-2010, 11:44 AM
alistairsam's Avatar
alistairsam
Registered User

alistairsam is offline
 
Join Date: Nov 2009
Location: Box Hill North, Vic
Posts: 1,815
thanks for clarifying that.

I had mistakenly assumed that a guide camera with an ST4 port can be used as a standalone guider that can send correction pulses. clearly not the case.

I was hoping to do away with the laptop and use the guide camera and my mcu alone. I guess I need to do a lot more research for that as I'll have to analyze the ccd image on my mcu to generate correction pulses required.

understood what you mentioned about pulseguiding. I guess it makes more sense for the software to correct the mount directly rather than through the guide camera and its st4 port.
Reply With Quote
  #9  
Old 30-12-2010, 12:00 PM
wasyoungonce's Avatar
wasyoungonce (Brendan)
Certified Village Idiot

wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,312
Quote:
Originally Posted by alistairsam View Post
...I had mistakenly assumed that a guide camera with an ST4 port can be used as a standalone guider that can send correction pulses. clearly not the case.

I was hoping to do away with the laptop and use the guide camera and my mcu alone. I guess I need to do a lot more research for that as I'll have to analyze the ccd image on my mcu to generate correction pulses required.

understood what you mentioned about pulseguiding. I guess it makes more sense for the software to correct the mount directly rather than through the guide camera and its st4 port.

Some of the newer guide cameras do not need a computer..I added some links above but here they are again..here and here, here and I guess many more in the future. really ST4 guiding is...old and not keeping up with today's standards.

Pulse guiding is an excellent adaptation..as the pulse can also contain "rate" information. Generally with PHD and my mount controller I set the control pulses (ST4 correction pulses) rate to lets say .5x..that is .5 sidereal rate. So any corrections in the ST4 port are at .5 sidereal.

But this is a pre-set...and to tell the truth not the best method. Really what you want is the pulse to also contain "rate of change" aka to change the rate of the correction as well.

I believe the SG4 does this.

In reality it would be better to pulse guide and input these to the mount maybe via serial/USB not ST4.

All that said..ST4 works...it's simple that's why it's lasted so long. It's time is well and truly up though.
Reply With Quote
  #10  
Old 30-12-2010, 01:09 PM
alistairsam's Avatar
alistairsam
Registered User

alistairsam is offline
 
Join Date: Nov 2009
Location: Box Hill North, Vic
Posts: 1,815
sorry, what I meant by saying that the guidecamera cannot be used as a standalone guide source was with reference to the standard guide cameras or the cheaper ones.
As you mentioned, the slightly more expensive ones are standalone.

The Skywatcher SynGuider looks like an attractive option. so does the Orion StarShoot Solitaire.
Reply With Quote
Reply

Bookmarks

Tags
autoguider, camera, guide, lx200, st4

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:09 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Celestron Australia
Advertisement
NexDome Observatories
Advertisement
Meade Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
SkyWatcher Australia
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement