Arduino to Python: How to import readings using ser.readline() into a list with a specified starting point?

Question

This is quite a specific query so please bear with me.

I have 14 ultrasonic sensors hooked to an Arduino sending live readings to the serial monitor (or Pi when I plug it in) . The readings are sent as follows, with a new line between every 2 digits (except Z).

Z 62 61 64 63 64 67 98 70 69 71 90 XX 75 XX

These measurements are in cm. "XX" implies the reading is out of the two digit range. Z has been assigned as a starting point as the pi reads the sensors very fast and repetitively, to the point of 80 readings in a second or so. So ser.readline() gives multiple samples of the same sensors

When python reads the readings in ser.readline() it does not have a starting point. It may start at 70, XX or Z. I want to assign it into an accessible list so that:

array [0] = Z (always)

array [1] = 62 (first two digits)

array [2] = 61 (second two digits)

..

array [14] = XX (fourteenth two digits)

This is my code which unfortunately doesn't work as list is out of range:

import serial
ser = serial.Serial('/dev/ttyACM0',115200)

print ("Start")

overallcount=1 #initialise 2 counters
arraycount =1
array = [] #initialise 2 lists
line = []

while True:
    while overallcount<30: #read 30 random readings from Arduino
        ser.readline()      
        print(str(overallcount)) #print reading number
        while arraycount<15:     #Number of readings to fill the array to be made
            for line in ser.readline():
                if line == 'Z':         #If element in ser.readline is "Z"
                    array[0] == line    #Assign first list element as Z (starting point)              
                arraycount=arraycount+1 #Iterate through until 14 sensors are read
            arraycount=1                #reset counter
        overallcount=overallcount+1     #Iterate through 30 random Arduino readings
    overallcount=1                      #iterate random counter

If you could please tell me what I'm doing wrong, or if there is a better method for this I'd really really appreciate it!

Thank you

Answer 1

How about this? Note that your checks overallcount<30 and arraycount<15 should really be overallcount<=30 and arraycount<=15.

import serial
ser = serial.Serial('/dev/ttyACM0',115200)

readings = [] # Array to store arrays of readings
reading_id = 1 # Id of current reading
random_lines_expected = 30 # NUmber of random lines
num_sensors = 14 # Number of sensors

def read_random():
    for _ in range(random_lines_expected):
        ser.readline() 

read_random() # Read initial random lines
while True:
    print "Reading #", reading_id
    reading = [] # Initialize an array to collect new reading
    while ser.readline().strip() != 'Z': # Keep reading lines until we find 'Z'
        pass
    reading.append('Z') # Add Z to reading array
    for _ in range(num_sensors): # For 14 sensors...
        reading.append(ser.readline().strip()) # Add their value into array
    readings.append(reading) # Add current reading to the array or readings
    reading_id += 1 # Increment reading ID
    #read_random() #Uncomment this if random follows each series of readings