ST4 guide cables, different types

[Guest]

Hi all,

I have a question someone may be able to answer,

I have recently found out that not all ST4 connections on guide cameras and mounts are wired the same, some cameras for instance the Atik and QHY5 have a couple of the wires reversed, the Atik has pin 3 in the connector for the RA- movement , while the QHY has this pin set for RA+, so how does this work with the mounts, has anybody ever had issues with incorrect guide commands

I have only ever seen ST4 cables for sale, with no mention of different ones for different cameras, or does the guide software compensate for all this?

Very confusing

Here are the pin connections for different cameras

ST4 Compatible Cable (meade, Atik, etc)

RJ11 6P6C

1 = No Connection

2=Ground

3=RA-

4=Dec-

5=Dec+

6=RA+

The Standard ST4 Cable (Qhy, Skywatcher)

RJ11 6P6C

1 = No Connection

2=Ground

3=RA+

4=Dec+

5=Dec-

6=RA-

Notice the difference with pins 3, 4, 5, and 6

Olly

[steppenwolf]

Ignoring the top connector on this diagram (this is from my own data box), the following is, to the very best of my knowledge, the 'industry standard' wiring:-

[TCWORLD]

I don't think it really matters if the RA+/- and DEC+/- are reversed. If you think about it, what happens if you rotate the guide cam by 180 degrees? (RA+ becomes RA- essentially, the same for DEC). In fact what happens if you turn by 90 degrees - DEC and RA need to swap.

When the guidecam or PHD or whatever does calibration it will be able to account for these changes by say - move RA+ a bit, then move RA- to re-centre whichever way it moved is then part of the calibration.

As long as RA/DEC are pins 3-6 and GND is pin 2, they should all be perfectly compatible. I have however seen designs where a completely different ordering is used (RA+, GND, RA-, DEC+, GND, DEC-), that's when things don't work.

[Guest]

Ok so if I use a standard ST4 cable on my mount which is a meade, and like meade they have to be different, then my DEC and RA are reversed compared to standard ST4 connections, this is my issue, but you are saying it won't matter when guiding, am I correct?

Even though the camera will be sending for example a " move east command" down the cable, but when it reaches my meade mount the command will be hitting the pin on the connector for move west!! Because mine are reversed

Sorry for seeming a bit thick, but you see where I am coming from

Olly

[TCWORLD]

Doesn't matter. That's what calibration is for. It decides how the signals correspond to movement.

Imagine this - If you put a guide camera on a Newt, it will see the image as it was when it entered the eyepiece. So in this case RA+ = West, RA- = East.

Now connect the same camera to a Refractor, it may see the mirror image of what entered the eyepiece. So in this case RA+ = East, RA- = West.

Notice how it switches? The same happens if you change the orientation of the camera.

It doesn't really matter what the signals do - you could even wire the RA+ to the DEC- and it would still work. As far as the camera is concerned there are only four directions it can move, Up, Down, Left, Right. When you connect the mount it basically has to map those four on to the four ST4 signals. It may find for example that UP = DEC+ and RA-.

[Guest]

Doesn't matter. That's what calibration is for. It decides how the signals correspond to movement.

Imagine this - If you put a guide camera on a Newt, it will see the image as it was when it entered the eyepiece. So in this case RA+ = West, RA- = East.

Now connect the same camera to a Refractor, it may see the mirror image of what entered the eyepiece. So in this case RA+ = East, RA- = West.

Notice how it switches? The same happens if you change the orientation of the camera.

It doesn't really matter what the signals do - you could even wire the RA+ to the DEC- and it would still work. As far as the camera is concerned there are only four directions it can move, Up, Down, Left, Right. When you connect the mount it basically has to map those four on to the four ST4 signals. It may find for example that UP = DEC+ and RA-.

Ok thanks for the explanation , I think I get it now,

Appreciate it

Olly

[perfrej]

Just beware! The ST-4 "standard" uses the same connector at both ends. The companies that put the connector there sometimes uses the same order of pins on the mount as on the camera, sometimes not. Therefore, check if you need a straight or reverse cable. I have seen this issue.

I can recommend not using the ST-4 port at all in favor of pulse-guiding via ASCOM.

/per

[ollypenrice]

And to make matters worse 'ST4' cables are not ST4 at all! The original ST4 used a physically different cable though presumably it established the wiring convention.

A positive in favour of pulse guiding is that it does away with the awful 'ST4 mini' cable on the Lodestar. If AP is 'cable hell' then this silly little thing just turned up the boiler in the fiery pit!

Olly (Another one!)

[Guest]

And to make matters worse 'ST4' cables are not ST4 at all! The original ST4 used a physically different cable though presumably it established the wiring convention.

A positive in favour of pulse guiding is that it does away with the awful 'ST4 mini' cable on the Lodestar. If AP is 'cable hell' then this silly little thing just turned up the boiler in the fiery pit!

Olly (Another one!)

I guide at the moment via the handset using a USB to serial cable and ascom with pulse guiding, and it works a treat, but I have alway used a Meade DSI so no ST4 port so had to guide this way, I have sold that now and bought an Atik Titan as a guide camera which has ST4 so though I would use it, I have the APM909 for my mount and this has the CCD port.

So,are you saying to stick with the Ascom and pulse guide method? Because that Would be easier for me, but i though that was a bit dated now and not as quick or reliable as the ST4 method, so am I wrong here?

Olly (the one in England)

[perfrej]

Yep, stick with pulse guiding. Much more accurate. As you already have it working, keep it

Per (the one in Sweden)

[ollypenrice]

Per (the one in Sweden)

The only one!!

lly

I must try pulse guiding but I have had a torrid time with ASCOM. Before you tell me it's me, I can promise you that I have been unsuccessfully abetted by a Manchester University academic in the field of computer physics!

[perfrej]

OK, there are 167,662 Pers in Sweden (males) and 5 women (what?) It is the fifth most common name. But I agree; there is only one ME! Moaaaahahahahahahaaaaa!

I'll teach you pulse guiding over a glass of Chablis, Mr Penrice!

/per

[perfrej]

This is a test:

Chablis (C ha bl i s)

/per

[perfrej]

Interesting. You cannot mention good French white wine, but how about Champagne (Cha m pa gn e)?

[perfrej]

OK, someone with interest in the Wine industry wrote the forum software... My glass of Cha bl is is empty, so...

/per

[RikM]

I used to like Chablis

I am really not clear on the advantages of ST4 vs. pulse guiding or vice versa. I normally just control the mount from the handset but am planning to give EQmod a try once I have an obsy based set up in a few weeks. This means I could try pulse guiding rather than using the ST4 cable that came with my QHY5 but I am not sure why I would want to.

[Davey-T]

One less cable to wrap itself round the mount, I usually get the scope aimed at the nights target before plugging in cables to Laptop, and try to avoid meridian flip

Dave

[perfrej]

I don't know if caught the [Removed word}thing with Chablis before, but I guess they fixed. Good! The moderators are sharp and keep an eye on things, not only correcting wrongdoings but also errors in the system. Excellent.

Why pulse-guiding? I give you two reasons:

1) One less cable, one less interface

2) Accuracy

Point 2 is a valid and important one. The accuracy with small relays and software having to turn something first ON and then OFF and hope that the computer didn't get caught in something of higher importance in the time in between the two is just not enough. Pulse guiding works differently. First, the guide application calculates the exact time that the mount should be adjusted in its tracking. It then doesn't have to worry about timing that duration of movement (as it has to do with ST4). Instead, the mount's ASCOM driver, or for mounts that has native pulse-guide support the mount itself, times the pulse.

This way, the accuracy is 100 per cent, and the guiding algorithm doesn't get into over- or under-corrections, and hence guiding graph gets a much smoother look without oscillations.

Isn't that cool?

/per

[perfrej]

One less cable to wrap itself round the mount, I usually get the scope aimed at the nights target before plugging in cables to Laptop, and try to avoid meridian flip

Dave

Dave, you have to accept and possibly even love meridian flips. They are a natural part of life. With my setups, a flip results in the target being smack dab in the middle of the CCD every time. Since I do not guide there is no re-acquiring of guide stars to take into account, so there is no bother there either. And the cables are all tied up into one, hence no tangling.

I usually route the cable from the scope via the counter-weight bar; works like a charm!

Life is good!

/per

[RikM]

I route my cable back to the PC in a loom. I use velcro ties on the tripod leg to make sure the cables don't cause a pull on the mount axis. A loom also makes setting up faster and easier. (photo poached from tich)

I will definitely try pulse guiding because the guide camera end of my ST4 cable has a temperamental connection. 

[perfrej]

Excellent cable routing! Actually, it is the first time I see someone thinking along the same lines asI do.

/per

[Davey-T]

Dave, you have to accept and possibly even love meridian flips. They are a natural part of life. With my setups, a flip results in the target being smack dab in the middle of the CCD every time. Since I do not guide there is no re-acquiring of guide stars to take into account, so there is no bother there either. And the cables are all tied up into one, hence no tangling.

I usually route the cable from the scope via the counter-weight bar; works like a charm!

Life is good!

/per

Rig2.jpg

Thankyou Per, I'm still saving for the 10 Micron

Dave

[Tyler]

Can you use cat 6 cable 

[Davey-T]

31 minutes ago, Tyler said:

Can you use cat 6 cable 

Hi Tyler and welcome to SGL, this is  really old thread so you'd be better off starting your own new topic in one of the beginners getting started forums.

No reason you can't use CAT6 cable but it may not stand up to a lot of abuse, even the manufactures cables fail at the plug eventually.

Dave