Wednesday, December 28, 2011

Poor Man's Vixen Starbook

Here is how I butchered a NGC Sky Vector Digital Setting Circle (DSC) to connect it to a SkyWire.

SkySafari from Southern Stars is a great planetarium application for the Apple devices and now Android. It's the closest to the old Starry Night Backyard that I knew and loved a decade ago.

One of the neat tricks that SkySafari has is its ability to control most any telescope via a wireless dongle called a SkyFi, or a cheaper wired serial dongle called a SkyWire:

The SkyWire is basically a serial port that connects to the port on the bottom of every iPod, iPhone, and iPad out there.

I had already previously used the SkyWire to control my Celestron CGEM mount, but the CGEM is currently in the doghouse because its GoTo's are darn unreliable. I already had an NGC Sky Vector that I snagged for a hundred bucks off Astromart. The Sky Vector has an RJ-11 jack for a serial connector to a PC (or SkyWire) but I didn't have an RJ-11 plug (or crimper) handy. I did however have a DB-9 female connector, so I decided to swiss-cheese the Sky Vector casing.


After two runs with a 6mm drill bit:

And much later after much dremel-ing:

The Sky Vector PCB (note the little Tangent Instruments label) with its vacuum-fluorescent display and minimalistic four-button interface:

Contrary to my belief (which caused a lot of head-scratching and gnashing of teeth) the RJ-11 jack is soldered to both sides of the PCB, and the correct pins to solder to.. are not obvious. Only three wires are needed: RX, TX, and GND. And I got them all wrong.

The correct pinout according to Southern Stars. Use the third column ("Southern Stars SkyFi") and fifth column ("Celestron, Astromaster, others").

So basically it's DB9 pin 3 to RJ-11 pin 3; DB-9 pin 5 to RJ-11 pin 4 (this is the ground pin); and DB-9 pin 2 to RJ-11 pin 2. More information albeit with not as nice-looking diagrams.

After several bouts of soldering:

Buttoned it up..

and in action (telescope mount not shown):

I noticed that SkySafari couldn't talk to the Sky Vector initially (although I could using a USB serial adapter and RealTerm which is a good HyperTerminal replacement). Turns out my V 3.65 Sky Vector doesn't respond to queries about its maximum encoder resolution, I had to hard-code these into SkySafari.

Next stop.. real alignment. Weather's pretty bad so I just did a simulated/fake align to verify operation.

The nice thing about SkySafari is that you can sync on anything on the screen. Doesn't have to be from a small list of alignment stars.

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