The e-paper display I have makes use of the UART on the GPIO which collides with the GPS. I decided to switch to an OLED display, which only uses the I2C.

It is a 1.3" 128x64 pixel display using the SH 1106 controller. 

Use raspi-config to enable the I2C and install the i2c tools:

sudo apt-get install i2c-tools

Wiring is easy but requires some soldering.:

Check if the display is detected:

i2cdetect -y 1

Output should show a 3c:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         

I found the some python libraries here: 

sudo apt-get install python-dev python-pip libfreetype6-dev libjpeg-dev build-essential
sudo -H pip install --upgrade luma.oled

Installation and building will take some time. Don't panic. 

There is some nice example code available if you want to play around before continuing. This will also make sure your display is working correct.

You might want to clone the git repo from here: https://github.com/rm-hull/luma.examples. Before you need to install the git client:

apt-get install git 

git clone https://github.com/rm-hull/luma.examples.git

The examples default to the ssd1306 display driver, but mine is using a sh1106. So you need to run the example scripts with option -d sh1106. Else the display looks broken, but it is just using the wrong driver.

Here is a picture running the clock demo:

Yes, I already made a 3D printed case for everything. Not yet perfect, STL files are in the files section.

I like to keep all the bash and python scripts at /home/pi/. So this time not working as root.

Let's create a new file:

nano get-gps.py

This is the script:

#!/usr/bin/env python

import sys
import time
from gps3 import gps3

gpsd_socket = gps3.GPSDSocket()
gpsd_socket.connect(host='127.0.0.1', port=2947)
gpsd_socket.watch()
data_stream = gps3.DataStream()

def getgps():
   for new_data in gpsd_socket:
       if new_data:
            data_stream.unpack(new_data)
       if data_stream.TPV['mode'] != 'n/a':
            mode = data_stream.TPV['mode']
            latitude = data_stream.TPV['lat']
            longitude = data_stream.TPV['lon']
            time.sleep (2)
            if mode == 3:
                return (latitude, longitude)
                break

def dms(deg):
    m = (abs(deg) - int(abs(deg))) * 60.0
    s = (abs(m) - int(abs(m))) * 60.0
    return (int(deg), int(m), int(s))

def celestron(deg):
    c = dms(deg)
    return "{0:d} {1:d} {2:d} {3:d}".format(abs(c[0]), c[1], c[2], 0 if(c[0] >= 0) else 1)

coordinates = getgps()
print "{0} {1}".format(celestron(coordinates[0]), celestron(coordinates[1]))

Basically I took Dan Gardners script which takes GPS coordinates and returns it into the right format for the Celestron and added the capability to get the data from GPS. I'm not very happy with the for-loop and the break, as I don't like breaks in general. I might need to improve my python skills a little.

Don't forget to change permissions:

chmod +x get-gps.py

And give it a try:

./get-gps.py

After a few seconds (and if your GPS has a 3D fix) you should get an output like this:

pi@raspberrypi:~ $ ./get-gps.py
48 5 30 0 11 32 8 0

 Finally let's put everything together:

nano hc-location-gps.sh

Copy & Paste this:

#!/bin/bash

readonly serial=/dev/ttyUSB0

location=$(/home/pi/get-gps.py)

if [ ${?} != 0 ]; then exit; fi

stty -F ${serial} 9600

HEX="\\\\x%02X"
unset FORMAT
for i in {1..8}; do
  FORMAT="${FORMAT}${HEX}"
done

echo "Location: '${location}'"
hex_text="$(printf "W${FORMAT}" ${location})"

echo "Writing location to HC: '${hex_text}'"
echo -ne "${hex_text}" > ${serial}

Connect your hand controller and give it a try:

./hc-location-gps.sh