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Building a HomeBrew GPS for the Celestron Nexstar Telescope AUX bus

This began as an outshoot from a thread at the Cloudy Nights astronomy site.
I suspect there are quite a Celestron telescope owners who would love to build their own SkySync compatible GPS module.

Well, it is a lot easier than it may first appear. Here, I will assemble a HomeBrew GPS module, with simple step-by-step instructions. This version uses a SparkFun Pro Micro board. Older designs used a Pro Mini board instead.

Click here for the Arduino source code for this project, which also requires the TinyGPS++ library to be installed within the Arduino IDE.

To begin, click on the first photo below.

The parts required include: a wooden tongue depressor (or similar item), a Beitian BN-180 GPS module, a genuine Sparkfun branded 5V/16MHz Arduino Pro Micro board, one 100K ohm resistor, two 1N4148 diodes, and a short length of 6-conductor flat cable with a 6P6C RJ12 plug on one end.Any resistor from 50K to 100K will probably work. And the diodes could be any type such as 1N4148, 1N5817, or 1N4007 etc..The Pro Micro board must be a Sparkfun branded one, because those can safely handle +12V power from the Celestron AUX connector. No-name clone boards nearly always go up in smoke, because they skimped on the $2 voltage regular chip.
parts 		Here is the wiring diagram for this project.
promicro-gps 		First step is to stick the BN-180 and Pro Micro board down onto a segment of the tongue depressor, using double-sided sticky tape.
stuck_down 		Now wire up the BN-180 to the Pro Micro, and also attach the resistor and the diode for the TXO line as shown. The black striped end of the diode goes closest to the TXO pin.
gps_wired 		Also install the second diode to the RAW pin, with the black striped end closest to the RAW pin.
12v_diode 		Next, secure the cable to the back side with two cable-ties, as shown. This will keep it from moving around and breaking wires while the connections are made in following steps.
cable_ties1
Here's the top view of the two cable ties. Don't worry about that crooked white connector on the BN-180 -- it can be pushed firmly back into place at any time during the build.
cable_ties2 		Here is the completed wiring, per the original diagram. All connections now made, including the _12V (red in this case) wire from the AUX cable to the diode on RAW.
fully_wired 		UPDATE: The Pro Micro gets too hot when completely encased in heat-shrink, so I have now cut away the enclosure from the first 2cm or so back from the USB connector, to allow it to cool. The photo does NOT show this. A bit of clear heat-shrink tubing is melted around the assembly to lock everything in place, making for a nice and slim protective enclosure.
packaged 		The completed GPS accessory, which can just be plugged into the mount and left to dangle; no other form of attachment is necessary.
all_done
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