GPUSB output and relays?

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mdurkin
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Location: Forest Hills, NY

GPUSB output and relays?

Post by mdurkin » Mon Aug 24, 2009 1:19 pm

Hi,

Last week I bought the GPUSB Shoestring adapter and an SBIG relay box hoping that the combination would work on my old Celestron mount. The mount only has an RJ-11 port for the hand controller. I wired my laptop to the Shoestring adapter, then connected to the relay box, then then finally to the hand controller port. When running the test software on my laptop, I didn't notice any reaction with the telescope motors. After reading the documentation for the SBIG relay box, it looks like the relays need 12V to close the switch, which the GPUSB adapter does not provide.

So instead of modifying the hand controller, I want to make my own relay box that will take the output from the Shoestring adapter, and make the appropriate connections on the Celestron mount. Can I make a relay box based on GP1 in the HCModGuidance PDF, without the voltage from the hand controller? My guess is that I need to have relays that the GPUSB will be able to close without another voltage source, and I wasn't sure if that was possible.

Thanks.

-Mike Durkin

dpanderson
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Re: GPUSB output and relays?

Post by dpanderson » Mon Aug 24, 2009 1:50 pm

Starting with the GP1 schematic as you state is one possibility. A USB port can only put out 100mA, so you'll need to make sure each relay draws less than 50mA, because there could be two of them on at the same time.

If you could find some information on the handcontroller port for the mount, I think it is quite likely that you could interface the GPUSB directly to this port without the need for a relay box. Although the output drivers in the GPUSB are solid state, you can think of them as normally-open switches that short to ground (pin 2) when they close.
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

mdurkin
Posts: 13
Joined: Wed Jul 25, 2007 5:43 pm
Location: Forest Hills, NY

Re: GPUSB output and relays?

Post by mdurkin » Mon Aug 24, 2009 4:18 pm

Doug,

Thanks for the reply.

I wrote back about this a couple of years ago and included a couple of images of the hand controller circuit board:

Image
Image

And the drive itself:

Image

From what I've been able to tell, the RA and DEC buttons are switches that connect pins 3,4,5,6 to pin 2. (pin 1 being the white wire, and pin 6 being the blue wire)
I THINK that the focus buttons connect pins 3 and 4 to pin 1. The drive is powered by a 9 V battery.

I did try to connect the Shoestring adapter directly to the hand controller port, however it didn't seem to have any effect when running the test software.

Sorry, I don't have a lot of experience with tracing circuits, even though I know this is a simple one. Let me know if this makes sense or if you need further info.

-Mike Durkin

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Re: GPUSB output and relays?

Post by dpanderson » Mon Aug 24, 2009 4:30 pm

Can you provide a picture of the other end of the handcontroller cable (i.e. the end that plugs into the jack on the mount) so I can see the colors of wires at that end?

Thanks,
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

mdurkin
Posts: 13
Joined: Wed Jul 25, 2007 5:43 pm
Location: Forest Hills, NY

Re: GPUSB output and relays?

Post by mdurkin » Mon Aug 24, 2009 4:53 pm

Doug,

It's going to take me a while to get back to you on that since I don't have the hand controller readily available. It will probably be about 2 weeks before I can get a hold of it.

I may have used the wrong term by calling the connector an RJ-11. I can tell you that it is definitely 6P6C (6 position, 6 conductor) interface (RJ-25??). I just can't remember if the order of the wires on the mount side is: white,black,red,green,yellow,blue
or the mirror image: blue,yellow,green,red,black,white
It is definitely one of those two sequences.

I found this image where some one seems to have takes the parts of the drive electronics and attached them to a different motor:

http://www.cloudynights.com/classifieds ... -large.jpg

Let me know if that helps,

-Mike Durkin

dpanderson
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Re: GPUSB output and relays?

Post by dpanderson » Mon Aug 24, 2009 6:29 pm

Unfortunately there is not enough resolution in that image near the connector to make out the colors.

From tracing the pictures of the printed circuit board that you posted, I am surprised that the GPUSB won't drive the handcontroller port directly. That is why I was wondering about the connection into the jack on the mount, its the only thing I could think of that might be standing in your way.

Looking forward to seeing the picture of your cable end...
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

mdurkin
Posts: 13
Joined: Wed Jul 25, 2007 5:43 pm
Location: Forest Hills, NY

Re: GPUSB output and relays?

Post by mdurkin » Mon Aug 31, 2009 11:32 pm

Hi Doug,

I don't yet have a picture of the hand controller, but I wanted to verify something about the GPUSB adapter.

So I borrowed some one's multimeter and ran GPUSBCheck using the multimeter on the contacts on the top of the adapter. During my test, there isn't any cable attached.

So assuming I am reading the multimeter correctly, the voltage across pins when I press the appropriate button is coming out at about -0.38V. The resistance when I press the buttons reads about 13K Ohms (> 2 million if the button is not pressed). Do those numbers seem correct if I am only using the USB port on my laptop for power?

Thanks,

-Mike Durkin

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Re: GPUSB output and relays?

Post by dpanderson » Tue Sep 01, 2009 7:37 am

Mike,

The top two topics at this forum location:
viewforum.php?f=3
explain how to check the GPUSB using a multimeter. The first one explains how to do it when connected to the mount, the second one explains how to do it when not connected. The best way is using the "diode check" function of your multimeter if it has one.

Given the change in resistance you observed, I am guessing it is working.
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

mdurkin
Posts: 13
Joined: Wed Jul 25, 2007 5:43 pm
Location: Forest Hills, NY

Re: GPUSB output and relays?

Post by mdurkin » Mon Sep 21, 2009 4:31 pm

Hi Doug,

I just wanted to let you know that everything looks to be working fine. I had my first chance to try out the adapter this weekend and took my best image of M45 so far:

Image

I stacked 10 frames, each 2 minutes long. You can see some spherical aberrations since this was cropped from the top edge of the field of view, but the stars near the center look spherical enough.

Thanks again for all the help.

-Mike Durkin

dpanderson
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Re: GPUSB output and relays?

Post by dpanderson » Mon Sep 21, 2009 4:49 pm

Very nice picture, Mike. Congratulations, and thanks for sharing it.
Doug Anderson
Shoestring Astronomy
http://www.ShoestringAstronomy.com

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