Raspberry PI: Transmitting Telemetry via UHF
Equipment used:


UBlox Neo 6M GPS
NTX2 UHF transmitter
Raspberry Model B

GPS

The GPS uses 3.3V so connect the GPS to the appropriate GPIO pins for 3.3V working 









 
 Install the GPS software


#apt-get install gpsd gpsd-clients python-gps
 
 
Then edit /boot/cmdline.txt


ammend the "ttyAMA0" parameter to read


dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait


 edit /etc/inittab


comment (add a hash #) the line below "#Spawn a getty on Raspberry Pi serial line" like this:


#T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

 
 edit /boot/config.txt


 insert to set the baud rate for the neo 6M to 9600bps



init_uart_baud=9600

edit /etc/default/gpsd:
and change the DEVICES to indicate "/dev/ttyAMA0"

Reboot and test the gps data. You can test the rx data with minicom :

#minicom -b 9600 -o -D /dev/ttyAMA0 
you should see a stream of gps info

Run gpsd 

# gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock
and you can check the incoming data with cgps -s
UHF transmission
Run gprx on the mac to receive the 434 Mhz uhf signal and dl-fdigi to decode the audio that is being sent with the carrier.






 




 

Set the serial port to the correct settings:
# stty 50 cs7 cstopb < /dev/ttyAMA0


I run a quick cycled message to see if I can pick up the message via audio.

# while x=1; do echo Hello Out There > /dev/ttyAMA0; sleep 2; done
I pulled up quick script (be careful I said it was quick)

#!/usr/bin/python

import os
import serial
import time
import crcmod

x_list = []
y_list = []

def send(data):
 NTX2 = serial.Serial('/dev/ttyAMA0', 50, serial.SEVENBITS, serial.PARITY_NONE, serial.STOPBITS_TWO)
 NTX2.flush()
 NTX2.write(data)
 print "sent "+ data
 NTX2.close()


while True:
 gps = serial.Serial('/dev/ttyAMA0',9600, timeout=2)
 line = gps.readline()
 if 'GPGGA' not in line:
 continue
 #gps.flush()
 gps.close()
 time.sleep(0.5)
 print line
 fields = line.split(',')
 utc = fields[1]
 lat = (fields[2])
 N = fields[3]
 lon = fields[4]
 E = fields[5]
 FS = int(fields[6])
 NoSV = fields[7]
 HDOP = fields[8]
 msl = fields[9]
 uMsl = fields[10]
 Altref = fields[11]
 uSep = fields[12]
 DiffAge = fields[13]
 DiffStation = fields[14]
 if FS == 0:
 print "not synched"
 continue

 utc = float(utc)
 t = "%06i" % utc
 h = t[0:2]
 m = t[2:4]
 s = t[4:6]
 utc = str(str(h) + ":" + str(m) + ":" + str(s))

 y = int(lat[:2]) + float(lat[2:]) / 60.
 y = "%02.2f" % y
 if N == 'S':
 y = -y

 x = int(lon[:3]) + float(lon[3:]) / 60.
 x = "%02.2f" % x
 if E == 'W':
 x = -x

 print FS, x, y, NoSV, msl, DiffStation
 string = "DATA " + str(NoSV) + ',' + utc + ',' + str(x) + ',' + str(y) + ',' + str(msl) + "\n"
 send(string)





References:




http://ukhas.org.uk/guides:raspberrypi
http://diydrones.com/profiles/blogs/how-to-connect-3dr-gps-ublox-to-raspberry-pi
http://www.danmandle.com/blog/getting-gpsd-to-work-with-python/
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=41&t=53012
http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
http://elinux.org/RPi_Low-level_peripherals#General_Purpose_Input.2FOutput_.28GPIO.29
https://pypi.python.org/pypi/crcmod
https://github.com/ibanezmatt13/NORB