Laser-Pointer-Tracker-Abob

Problem Statement

I teach classes where we build amsat antennas and try to listen to satellites and the International Space Station. It is really hard to point to nothing at all, so I thought this would help (at least, during the night). It also has the handy dandy feature that it can be used to point out astronomical items if you modify the pyephem script barely.

The thing you have to 3D print

It is here: http://www.thingiverse.com/thing:1403736

Arduino Code

I used an uno to do this with a polalu stepper driver (one that takes steps and direction pulses) I also used a futaba servo. I also used the highest microstepping, which I believe is 1/16th microstepping.

Python Code

#!/usr/bin/env python
#Laser tracker thinger using pyephem to send serial alt-az commands to the arduino. 
#remember to set your ground station GPS coordinates!!!
#The line looks kinda like this => solution.lon, solution.lat = '-111.717379', '33.401926'

import time
import datetime
import ephem
import optparse
import sys
import serial

filename = "TLE.txt"

try:
   fo = open("/home/pi/" + filename, "r")
except:
   print "TLE file not found - error"
   print filename
   sys.exit(1)

#Read the first three lines of TLE.txt
line1=fo.readline()
line2=fo.readline()
line3=fo.readline()
fo.close

#port = serial.Serial("/dev/ttyAMA0", baudrate=115200, timeout=3.0) #Pi pins
port = serial.Serial("/dev/ttyACM0", baudrate=115200, timeout=3.0) #Arduino USB 

sat = ephem.readtle(line1, line2, line3)

solution = ephem.Observer()
solution.lon, solution.lat = '-111.717379', '33.401926'
#solution.date = '2015-10-19 13:44:51.4584';

while True:
   solution.date = datetime.datetime.utcnow()
   sat.compute(solution) #defaults to NOW
   pi = 3.14159265359   
   
   if sat.alt < 0:      
      out_altitude = (180.0/pi)*sat.alt
      ser_altitude = int(0)
      out_azimuth  = (180.0/pi)*sat.az
      ser_azimuth  = int((180.0/pi)*sat.az*10)
   else:      
      out_altitude = (180.0/pi)*sat.alt
      ser_altitude = int((180.0/pi)*sat.alt*10)
      out_azimuth  = (180.0/pi)*sat.az
      ser_azimuth  = int((180.0/pi)*sat.az*10)
   
   print("Alt:{0:.1f} Az:{1:.1f}".format(out_altitude, out_azimuth))
   port.write("{0},{1}\n".format(ser_altitude, ser_azimuth))
   port.flushInput() #this might be why the thing is crashing, input buffer fills up??
   #print("Alt:{0} Az:{1}".format(ser_altitude, ser_azimuth))
   time.sleep(1)

TLE

A sample TLE file would look like this, but note that the code will only load the FIRST THREE LINES but it is nice to have them all in one spot, so I just shuffle them up to the top as needed.

NOAA 19 [+]             
1 33591U 09005A   16069.53289067  .00000138  00000-0  10001-3 0  9994
2 33591  99.0285  25.5538 0014613 136.4662 223.7665 14.12048620365077
Saudisat 1C
1 27607U 02058C   16069.10105181  .00000444  00000-0  83508-4 0  9996
2 27607  64.5542 106.6305 0076860 237.5124 121.8533 14.75091549710503
NOAA 15 [B]             
1 25338U 98030A   16068.51495196  .00000095  00000-0  58860-4 0  9997
2 25338  98.7831  72.4648 0011644 115.9718 244.2663 14.25708308926640