TIC-78 autoguide cable

Discussion in 'STF Series CCD Cameras' started by DarkStar, Mar 14, 2017.

  1. DarkStar

    DarkStar Standard User

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    Hi,

    i need some support for making/using the right type of cable for an ST-8XME. This is the connector where i need to plug it:

    [​IMG]
    Do i need a straight cable with colors identical in both plugs or i need an inverted one with colors sequence inverted in one plug?

    I wanna avoid to burn something on camera/mount ...
     
  2. Doug

    Doug Staff Member

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  3. DarkStar

    DarkStar Standard User

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    Thanks for the reply.

    I ask to myself why the original SBIG autoguider cable has pin colors inverted in one end, a lot of ST4 ports of today i discovered are similar to Celestron ones I posted above ...

    Is possible to damage something inside camera if I use a wrong cable? Voltages are always 5 volts, TTL.
     
  4. Doug

    Doug Staff Member

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    Unfortunately the so-called "ST-4 Standard", which dates back to the late 1980's, was very loosely defined. It was agreed upon by the telescope manufacturers in a very ad-hoc manner, and that has resulted in a lot of confusion between manufacturers of the mounts and the cameras. Ironically, the original SBIG ST-4 actually never had an RJ-12 connector on it; it had a DB-15 connector with many more connection options, and it needed an adapter cable to connect to an "ST-4 Jack" on the mount!

    Anyway, what usually happens if you plug it in flipped is that the mount tracks on Dec Negative continuously because it shorts the pin to ground. There is one small risk, and that's the "Not Connected" pin - that's a reserved pin that vendors are allowed to use for whatever they want.

    In the case of SBIG cameras, many models have a jumper inside that allows the camera to output power on this pin. It's used to power an optional external relay box. These days it is rarely used. By default the jumper is not installed.
     
  5. DarkStar

    DarkStar Standard User

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    Ok. Clear.

    I had found this old document which reports TIC-78 pins layout different from the actual documentation. Maybe did something change during years? Or maybe that layout refers not to the plug on the camera but to the cable jack ...
     

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    Last edited: Mar 15, 2017
  6. Doug

    Doug Staff Member

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    Nothing changed. One diagram is of the socket in the camera, the other is the end of the cable. The two are necessarily mirror images of each other.

    This is exactly what has led to the confusion over the years... the connections are often reversed because people misinterpret the diagrams, and there's no official standards document.
     
  7. Tony Lazar

    Tony Lazar Standard User

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    Hi Doug, could you help me with a specific example? I have two SBIG cameras - an STT-8300M and an ST-4000XCM - connecting to a Celestron CGE mount. Can I use one type of autoguide cable for both? Or do they each need a different type of cable? Can it be a regular RJ12 6P6C or does it have to be some custom-made TIC-78 with strange pin connections? (I plug into the ST-7-RC dongle on the ST4K, which I think does the translation for me.)

    And should it be straight (white wires on the left on both sides) or reversed (white wires mirror image on each side)? I've tried with a reversed RJ12 6P6C and get no motion in Y- but good motion in X+/X- with both cameras using CCDSoft (see image of calibration results). I'd really appreciate your help.
     

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  8. Doug

    Doug Staff Member

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    All SBIG cameras use the same cables. Yes it is an RJ12 6P6C connector, but they can be built in two different orientations so if you buy one it may be backwards.

    The cables we supply work with most mounts... though it is possible that there are mounts out there with the connections backwards. There are definitely other brands of cameras that have them backwards!

    Here is an excerpt from the STX manual showing the details of the cable:

    TIC.jpg
     
  9. Tony Lazar

    Tony Lazar Standard User

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    Thanks, Doug! This is what happens when you have all your cables in a rat's nest and forget which is which... Now it looks like the RJ12 cable between my Celestron CGE mount and both my SBIG ST-4000XCM and my STT-8300M is a reversed connection (pin 1 to pin 6). When I plug in a straight cable (pin 1 to pin 1) between the CGE and the ST4K, I get continuous Dec tracking as you describe above: "if you plug it in flipped the mount tracks on Dec Negative continuously because it shorts the pin to ground".

    But when I plug in a reversed cable, the ST4K calibrates well on X+, X-, and Y+, then slews at maximum rate in Y- for exactly the prescribed number of seconds. I get maximum slew rate (9) on Y- with the ST4K either in calibration or pressing the E-W-N-S buttons in CCDSoft (only South has the problem). I ran this with several cables; now I'm suspecting the RJ12 plug in the mount. Could you confirm that the cable between SBIG and Celestron should be a reversed pinout? And can you shed any more light on this puzzle? Or am I getting my North/South and +/- mixed up?
     

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  10. Doug

    Doug Staff Member

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    One of the problems with the informal "ST-4" cable standard is that there's no actual standard... I don't think it was ever formally published except in various vendor's user manuals. (And, ironically, the SBIG ST-4 never had an RJ-12 connector... it needed an adapter cable!) Some mount manufacturers, and even some camera manufacturers, have interpreted the pin assignments backwards. The "clips are on the same side" is the "official" way to do it. But you might encounter a mount where that tracks away continuously... in that case you need the opposite.

    So if I understand you correctly, the mount guides properly in three directions but slews at high speed in Y-. If that's the case then the problem is on the mount side. It doesn't sound like a connector problem - it might be something in the innards.

    The old Losmandy Digital Controllers would slew at full speed if you pressed a guide button, and then tapped the opposite button. Maybe other mounts do that? I don't know if that's a clue or not.

    I should mention that if your mount has ASCOM PulseGuide capability, it might be the path of least resistance to go that way at this point!
     
  11. Colin Haig

    Colin Haig Staff Member

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    One possibility is the Y- is being grounded. That usually means the orientation of the RJ12 connector is flipped.
     
  12. Doug

    Doug Staff Member

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    Actually, +Y would be grounded. Remember I said that opposite simultaneous inputs cause high speed slewing on some mounts? Maybe that's what is happening. +Y and -Y are both being actuated.
     
  13. Colin Haig

    Colin Haig Staff Member

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    Typo on my part, that's all.
     
  14. Tony Lazar

    Tony Lazar Standard User

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    So ASCOM guiding definitely works. Thanks for the suggestion! Sometimes a workaround is better than a solution...

    I was testing with CCDSoft & cable because it's so much quicker & more intuitive than SGP/PHD2 & ASCOM. The latter works, the former doesn't.

    I will test the idea that +Y getting grounded causes opposite simultaneous inputs in +Y and -Y which in turn cause high speed slewing in Dec. (I printed a color diagram to keep track of all the Pluses and Minuses and Rights and Lefts and Norths and Souths... but need more coffee to keep up!)

    Even though the RJ12 pinout only comes in straight or reversed, the Plus/Minus order of RA/Dec can be reversed as well. But guiding calibration should take care of that, so long as a ground is not involved. I'll test that as well.
     

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