I am advised that Shoe String supply two different units for the older and current Losmandy
Gemini GEM's. My understanding of the SBIG ST4 guider is that it is a "pull down" system.
Will someone please advise what is the essential difference betwee the two marketed units ?
differences in GPUSB for old an new gemini mounts
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Re: differences in GPUSB for old an new gemini mounts
Yes,there is a difference. Here is a note from our webpage http://store.shoestringastronomy.com/products_gp.htm:
"NOTE to Losmandy Owners: If you have a GM-8 or G-11 without the Gemini box, you will need the GPUSB or GPINT-PT. If you are using the NEW style Gemini box (the NEW style has a circular DIN connector to connect to the motors), then you will need the GPUSB or GPINT-PT. If you are using the OLD style Gemini box (the OLD style has a modular RJ-45 connector to connect to the motors), then you will need the GPUSB-AH."
As you state, the ST4 is a "pull down system" where the electronics act like normally-open switches to ground. The NEW Gemini box is compatible with this. The OLD Gemini box was designed to work with a "pull up system" where the electronics act like normally-open switches to the positive supply voltage.
"NOTE to Losmandy Owners: If you have a GM-8 or G-11 without the Gemini box, you will need the GPUSB or GPINT-PT. If you are using the NEW style Gemini box (the NEW style has a circular DIN connector to connect to the motors), then you will need the GPUSB or GPINT-PT. If you are using the OLD style Gemini box (the OLD style has a modular RJ-45 connector to connect to the motors), then you will need the GPUSB-AH."
As you state, the ST4 is a "pull down system" where the electronics act like normally-open switches to ground. The NEW Gemini box is compatible with this. The OLD Gemini box was designed to work with a "pull up system" where the electronics act like normally-open switches to the positive supply voltage.