#!/usr/bin/env python
from numpy import *
from math import *
import serial, time
import sys

#interface with pn6100A scale
#http://www.awscales.com/images/stories/scales/PN-6100A/main/PN-Series_manual_v2.pdf

try:
	ser_scale = serial.Serial(
		port='/dev/tty.usbserial',
		baudrate=9600,
		parity=serial.PARITY_NONE,
		stopbits=serial.STOPBITS_ONE,
		#xonxoff=True,
		bytesize=serial.EIGHTBITS)
	print(ser_scale.name)
except(OSError):
	print "Couldn't find the serial port"
	sys.exit(0)

def write(cmd):
	#print "sending: ",map(hex,cmd)
	ser_scale.write(cmd)
def read():
	msg = ['\x11']
	while( ser_scale.read(1) != '\x11'):
		print ser_scale.inWaiting()
	while( msg[-1] != '\x13' and len(msg)<100):
		msg += [ ser_scale.read(1) ]
	return msg

def request_weight():
	write( bytearray([1,ord('s')]) )
	time.sleep(.03)
	weight = read()
	if (weight[9] != 'g'): 
		print 'units are not grams!'
		sys.exit(0)
	return float(''.join(weight[1:8]))
def tare():
	write( bytearray([1,ord('t')]) )
	time.sleep(.1)
	print read()


tare()
for i in range(100):
	time.sleep(.1)
	print request_weight()

ser_scale.close()