Introducing OpenPlotter hats!!!

[GSAtlantic]

yep, I felt adventurous and tried to do a bit of python-coding on myself. Not that I am expert - if anybody has a better idea how to transform pulses in speed measurement, I am glad to learn:

Code:

#!/usr/bin/python
import RPi.GPIO as GPIO
import time
import os

GPIO.setmode(GPIO.BCM)
GPIO.setup(24, GPIO.IN, pull_up_down = GPIO.PUD_UP)

path = "/var/run/nmea.fifo"
os.mkfifo(path)

fifo = open(path, "w")
fifo.write('$VWVHW,,,,,0,00,N,,K\r\n')
fifo.close()

impulse_count = 0
NUM_CYCLES = 10
Counter = 10
while 1:
   start = time.time()
   for impulse_count in range(NUM_CYCLES):
       GPIO.wait_for_edge(24, GPIO.FALLING)
   duration = time.time() - start

   Counter = Counter + 10
   distance = Counter / 54737
   distancer = round(distance,2)
   speed = 15.2047222222 / duration
   speedr = round(speed,2)
   nmea = '$VWVHW,,,,,' + str(speedr) + ',N,,K\r\n$VWVLW,,N,' + str(distancer) + ',N\r\n'

   fifo = open(path, "w")
   fifo.write(str(nmea))
   fifo.close()

   time.sleep(0.5)

GPIO.cleanup()

The code counts 10 pulses and measures the time it takes. The paddlewheel documentation for the VDO says it counts  54737 pulses per 1nm, so this gives a basis for calculating speed in knots.

Then the values are transformed into NMEA-sentences and piped via a FIFO to kplex, which sends the NMEA to the cockpit.

Code:

[file]
name=logge
filename=/var/run/nmea.fifo
direction=in
persist=yes
checksum=no
strict=no

The script is started from rc.local so it runs as root. Security concerns are not so high on a standalone-system

Certainly there are ways to do this in a more elegant fashion... but I am not really a programmer.
Hope it helps though.

fair winds
Christian

Thank you for sharing Christian!  I may give this a go myself.

Much Appreciated!

Geoff