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Using ST-4 output from ZWO camera with 492 drive
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Hi all,
I have a ~18 year old G11 with 492 drive. Used to guide it with an ST-237 + relay box, but (a) the relay box disappeared at some point and (b) I no longer have a computer old enough to run the 237, although I am trying to change that. I do have a ZWO ASI290MC and wanted to try guiding with that. It's a one-shot colour cam which I know is not ideal for guiding but if it works OK I would pick up an ASI120 mini for guiding and use the 290 for imaging. According to ZWO all the ST-4 outputs are opto-isolated so it seems like this should all be safe to hook up - I'm just surprised that I haven't found a single example anywhere of anyone using ST-4 from a ZWO camera with a Losmandy non-Gemini mount. I haven't seen anyone saying it *won't* work, just... nothing.? Is anyone using this combination (ZWO ST-4 output with 492 drive) successfully, and if not does anyone see any big risk of damage ? I can live with it not working but with 492-based mounts out of production and 492 electronics out of stock I'm a bit more wary than usual.? Thanks, John |
¿ªÔÆÌåÓýYup I use a asi 120mc for guiding with my 492 using PHD2. ?Best move since st4 camera.Sent from my iDork On Sep 1, 2019, at 5:58 PM, John Bridgman <john.bridgman@...> wrote:
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I don't have a 492 but I repair Gemini 1 & 2's, Cameras.....and everything Astro put in front of me.....
All modern ST4 outputs are either opto-coupled out or transistor TTL "low" signals.?? Aka...the signal is a "low level" the opposite to a "high" (high= +5V).? So, ST4 these days outputs is "a signal low".?? The 492 Drive Hand-controller buttons switch ground (or "low") out the appropriate pin to command movement.? See attached diagram. Thus "yes" you can use your ZWO camera as an ST4 for the 492 drive as the HC and ST4 signals are essentially the same.? You will need that parallels these ZWO ST4 signals with the HC signals and your ST4 guiding will be limited to what G/S rate you have set in the system...the top LEDs:.3x; .5x; 2x....etc? But it should work fine at .5X.? Lastly you need to pay attention to the wiring of your ST4 to HC adapter cable to ensure it goes to the correct positions wrt to the HC buttons.? If you miss-wire it...don't fret it won't cause damage....just work the wrong way!? may help a little more in this. Cheers tell us how you get on. ? -- Brendan |
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In PhD2 click on the Tools tab. The first item is Manual Guide. If you set the Guide/Slew rate in the 492 panel to 16X you'll be able to see and hear the manual guide corrections. I use the Manual Guide at 8 or 16X to check cables (a common source of field failures for me) and to center on targets. It works fine, as long as I remember to set the Guide/Slew back to 0.5X afterwards! The whole reason for opto-isolators is to get rid of the problems with relays. The SBIG relay box, in my opinion, was a disaster waiting to happen with grounding and other problems - like no anti-kickback diodes with relay coils powered off (according to the SBIG schematic) your camera power supply. Scary as heck and the reason why the old 237 specification included the number of Joules of energy the circuit had to be capable of withstanding. Optos don't do that. I suspect your anxiety arose from hearing old horror stories associated with the original Gemini system, which had grounding conflicts with some guide devices. The Model 492 never had those problems to my knowledge. I've guided with the ST4 interface with optos on the 492 since 2006 with two different guide cameras wit their own optos and the Shoestring USB to ST4 box (GPUSB) with an old mono Meade DSI. Never a hiccup in any of it. So I think you're better off without the relays and the (my opinion) clunky 237 box and software. Send it to be recycled - don't invest in the past by trying to get a computer with a true parallel port. I ditched my old LX modified Celestron planetary camera (the original NextImager modified ala the MexImager mod of Freddy Diaz in Mexico City) that I used for guiding years ago rather than try to keep it running. That and the GP-INT (parallel port to ST4 opto-adapter from ShoeString) has been sitting in the spares box for over a decade. If you ever get a failure in the 237 you will be on your own repairing it and even getting parts. If you want to guide with a camera that does not have an integral ST4 interface, get a USB to ST4 box (called the GPUSB) from Shoestring Astronomy. If you order it direct it is cheaper than orders through astro-retailers. PhD2 (and PhD) will support that as the Mount interface under the Configuration menu. That and my Meade mono DSI-Pro have been my backup system for over a decade - they both still work with Windows 10. Mark Christensen |
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John Bridgman
Thanks Mark. I thought I remembered seeing comments about grounding concerns with 492 drive as well, but IIRC that was for the "no relay box" scenario. Will try it out next non-cloudy night.
If the weather stays like it has been the last week or so (clear & sunny daytime, cloudy at night) I may end up having to use one computer to drive the camera and another to generate a moving starfield I can track :(? If I am able to guide with the ZWO cameras (which now seems like a pretty sure thing) then I'll probably still try to resurrect the ST-237 so I can play with a cooled camera without further investment, but agree it's not going to be worth the hassle/risk to try guiding with it.? |
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