ser2ppm.py

# simple test program
# generating packets
# for the arduino board
# specify port number and a series of channel values
# for ppm output

import sys, serial
import time

BAUDRATE = 115200

# serial port number
# on windows python port numbering starts from 0: COM68 -> 67
# on linux: /dev/ttyUSB0

if (len(sys.argv) < 2):
	print 'usage: python',sys.argv[0],'/dev/ttyUSB0 1500 1000'
	exit(1)

port = int(sys.argv[1])
channels = sys.argv[2:]

count = 5 + len(channels) * 2

packet = bytearray()
packet.append(0x01) # start byte
packet.append(count) # length
packet.append(0x01) # type

try: # test for string to int cast
	for ch in channels:
		ch = int(ch)
		b = (ch & 0x000000ff)
		packet.append(b)
		b = (ch & 0x0000ff00) >> 8
		packet.append(b)

except Exception, e:
	print e
	exit(1)

checksum = 0

for p in packet:
    checksum += p

packet.append(checksum & 0x000000FF) # leave only lower checksum byte
packet.append(0x04) # end byte

for b in packet:
	sys.stdout.write(format(b, '02x'))
	sys.stdout.write(' ')

try:
	ser = serial.Serial(port, BAUDRATE)
	ser.flushInput()
	#ser = serial.Serial(port, BAUDRATE, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, bytesize=serial.EIGHTBITS, timeout=0)

except Exception, e:
	print e
	exit(1)

ser.write(packet)
ser.flush()
ser.close()