Having just installed a Gemini on my G11, I think I am now getting problems with ground loops - stuff freezing, errors from QHY5 in PHD etc
I have drawn a diagram of all the connections in my setup - and now that I have done that it is easy to see where the problems might be - but what do you do about it? I understand there are USB isolators - does anyone else use these? And where do you get them?
If I did get one or more isolators, where in the diagram would be best? If I put them in the obvious places between the netbook and usb hub and netbook and gemini, it still appears there would be the potential for a groundloop through 550D Power --> 550D --> USB Hub --> USB Hub Power...? Is that right? I have only basic knowledge about this stuff, so go easy if I have got it completely wrong.
I also have bought a couple of these in the past. They are very expensive but you think about it you are protecting equipment that is worth $$$. Here's an excerpt of an old correspondence on the Gemini Yahoo Group:
Hi all
I will once again put my 1 cent into this thread.
This is a message I have sent in the past.
The Gemini 1 is sensitive to Ground loops and static electricity. Of
course lighting is also a cause of failure.
I have had to replace about 20 RS232 chips and 3 guider chips do to
either Ground loop voltage, Static electricity, or
lighting in the case of 3 of them.
I would use an isolated adapter for the Guider input, if your camera
does not have isolated outputs.
If you are using a USB to serial adapter for the RS232 input, then one
of these 2 devices will help prevent
ground loops: http://www.keterex.com/kxusb150.php available from Mouser also. http://www.poscope.com/product.php?pid=23
I have both and they both work. You get a message that you could have a
faster connection
if you use a USB 2.0 device with the second less inexpensive device, at
least I did.
I use them with an FTDI based USB to serial adapter from Mouser called
the US232R-10
*http://tinyurl.com/l77sez *
I spent a lifetime in the electronics industry and while I knew of the effects of ground loops I never had any bother other than noise on secure data lines and this was cleaned by screens and single point earthing.
One interesting problem we often had with poor grounding was with mains equipment that had input filtering on the mains lines. If you did not have a good ground the gear would sit at half the mains voltage with respect to ground. Quite shocking!
Our G11/Gemini has no problems and runs in the field from the generator that also supplies a number of computers, telescopes, heaters, cameras etc.
I have never been worried about ground loops before on either my G11 or MI250 both use Gemini level 4.
Maybe I have just been lucky.
Who else with Gemin has had ground loop isues ?
Is this something we really need to worry about ?
I've had arcing between my hands and the alu tripod in very dry nights enough to drop the USB communication to the lappy and have a bit of a jolt myself but I haven't had any major damage. Ever. Although I have heard and read many times on the Gemini groups people having to change specific fuses on the gemini board or components linked to local surge in voltage. One cannot be too cautious IMHO.
As someone who has some amateur experience in electronics, I can say from looking at the wiring diagram there are many potential problems here. Add to this that you or your tripod acting as an earth return may present lower resistance than the earth returns in the electronics and you've got a potential nightmare. I'm not surprised someone might get a jolt once in a while. Operating this set up while standing in wet grass or on a concrete slab in bare feet could be a really bad idea.
I am not qualified or experienced enough to give advice regarding the approach to resolving this and ensuring its safe. I hope the thread attracts the attention of someone that feels comfortable doing this.
I did have some problems on the digital drive as well - if I ever looked through my cameras viewfinder I would get a little zap off the metal surround - felt like a pin sticking into my eyebrow (I keep the eyecup off so I can cover it when doing darks with that little rubber cover you find on the shoulder strap) This did sometimes upset the digital drive - the guidespeed and TVC would reset to their defaults.
But now with the G11 it is making the 550D not respond to on-camera button pushes (but will still control OK via USB), and I get an error out of PHD, and strange chopped up images from the QHY5.
Marc - that sounds like a good idea changing the USB-serial to go through the hub - actually very obvious - although it had't occurred to me . I do have a spare port on the hub.
those little poUSB things for $39 euros each might be the go...
Marc - that sounds like a good idea changing the USB-serial to go through the hub - actually very obvious - although it had't occurred to me . I do have a spare port on the hub.
those little poUSB things for $39 euros each might be the go...
Yeah I think so. Everything helps. I forgot to mention I even blue screened the laptop once . I had my hand holding the mouse on the Alu table and reached for the focuser... Zap! But then again I'm prone to statics. On a windy day I'll always zap on the car door when getting out. I even zap people. My mum's the same. Even worse. Maybe it's biological? Some people retain charge more than others. I don't know..
my next question is - do the ground loops only occur through USB connections - what about the power supplies - or are these isolated already by their transformers?
The path I am worried about (from my diagram) is
USB Hub Power --> USB Hub --> 550D --> 550 Power
for the isolators I imagine that if all USB stuff comes off the hub, then a single isolator between netbook and hub should be sufficient - surely I wouldn't need one off each hub port? It also looks like the isolators reduce the USB throughput a little...would this upset anything?
Our G11/Gemini has no problems and runs in the field from the generator that also supplies a number of computers, telescopes, heaters, cameras etc.
That implies the generator is providing the common ground.
The 240VAC is all on one power board? Not multiple power points which could be on different circuits and floating at different grounds.
Maybe start by opto isolating the ST4 cable (if you can find one of those) between the Gemini and the QHY5. If you can't find one of those, a USB one between the hub and the notebook. You might need more than one, maybe as many as three, or experiment to see which USB most needs it. The QHY5 gets its power from the USB so i guess you can't put an isolator between the hub and it.
I believe QHY5 and Starshoot autoguiders do have an Opto Isolated ST4 port from everything I have read.
I am confused by post below. If what I am reading is correct does this mean if everthing runs off same power source and same powerboard then ground loops are not an issue ?
I have never been worried about ground loops before on either my G11 or MI250 both use Gemini level 4.
Maybe I have just been lucky.
Who else with Gemin has had ground loop isues ?
Is this something we really need to worry about ?
I think if you are not having any problems with connected gear, then you probably don't need to worry. But with mine, it was affecting my laptop (the trackpad was almost unusable), and the camera (did not respond to any on-camera button presses, and would disconnect randomly which has never happened), and god know what it would do to the gemini over time.
Like Marc says - the stuff we have wired up is worth many thousands, if I can protect it with a $50 isolator, I'm in.
. I do have a spare port on the hub.
But then again I'm prone to statics. On a windy day I'll always zap on the car door when getting out. I even zap people. My mum's the same. Even worse. Maybe it's biological? Some people retain charge more than others. I don't know..
