A project to build an open source Nexstar-compatible GPS unit.
Celestron mounts, such as the CPC, come with a GPS unit built-in. However, they can go bad after a few years of service. This project will give you instructions on how to build your own compatible unit using off-the-shelf components and a little programming.
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Construct a replacement for the CPC mount, which already has a built-in GPS.
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Construct a SkySync-compatible unit for attaching a GPS to Celestron mounts that don't already have a GPS, such as the CGEM.
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Construct a replacement for the module in the Meade LX200GPS.
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Other mounts? Such as the Orion Atlas. (Don't know if the hand controller supports GPS.)
To build this, you will need:
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A GPS module, such as the uBlox NEO-6M. Commonly used by hoobyists for their quadcopters. Available for about $16.
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A small Arduino, such as the Pro Mini (5V version). Available for about $3.
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A TTL serial-to-USB adapter for programming the Arduino (if it does not have an on-board USB port already). Available for about $3.
Examine the three boards in your kit.
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The GPS module should have at least four pins: VCC, GND, TXD, and RXD.
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Locate the following pins on the Arduino: VCC, 5V, GND, TX, RX, and pins 2 & 3.
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The serial-to-USB adapter should have: 5V, GND, TXD, and RXD.
For ease of connection, you'll want to solder header pins onto the boards and use some DuPont cables to run wires between them. I suggest using right-angle header pins.
Here's a basic connection diagram:
GPS 5V ------------ 5V 5V ----------- 5V
GPS GND ----------- GND Arduino GND ---------- GND Serial Adapter
GPS TX ------------ PIN 2 TX ----------- RX USB ----------> PC
GPS RX ------------ PIN 3 RX ----------- TX
Once the Arduino has been programmed you'll remove the serial adapter and plug the Arduino directly into the existing connection in the CPC mount (inside the right-hand fork arm).
You will need to download and install the TinyGPS++ library.
Also needed is the SoftwareSerial library, which is built in to the Arduino IDE.