/nexstar_gps

Primary LanguageArduino

NexStar GPS

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.

Goals

  1. Construct a replacement for the CPC mount, which already has a built-in GPS.

  2. Construct a SkySync-compatible unit for attaching a GPS to Celestron mounts that don't already have a GPS, such as the CGEM.

  3. Construct a replacement for the module in the Meade LX200GPS.

  4. Other mounts? Such as the Orion Atlas. (Don't know if the hand controller supports GPS.)

Parts

To build this, you will need:

  • A GPS module, such as the uBlox NEO-6M. Commonly used by hoobyists for their quadcopters. Available for about $16.

  • A small Arduino, such as the Pro Mini (5V version). Available for about $3.

  • 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.

Construction

Examine the three boards in your kit.

  • The GPS module should have at least four pins: VCC, GND, TXD, and RXD.

  • Locate the following pins on the Arduino: VCC, 5V, GND, TX, RX, and pins 2 & 3.

  • 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).

Libraries

You will need to download and install the TinyGPS++ library.

Also needed is the SoftwareSerial library, which is built in to the Arduino IDE.