January 30th, 2013, 04:29 PM
Help with universal functions
I am fairly new to python, have just been playing with the arduino for a while, but got kinda bored with the limitations so that's why i'm now going for raspberry pi and python to control the arduino's outputs and receiving temperature/humidity data and so on from it.
The arduino only sends data when its requested from the pi, and the data integrity is checked by a crc32 checksum.
What my problem is, is that I want a universal function to split sensor data, check integrity and then print it. I have written a code that reads up to 2 sensors, but its kinda lame to have to add to the code if I want more of them, after all I want it to be universal, easier to read and reusable for other people too.
Would appreciate any pointers for how I could accomplish this! The code i'm now using has had alot of improvements since I started on it, but I still feel there's alot more to do. As this is the first "real" python program i'm writing, i'm learning alot! And I gotta say, python is great!
Anyway here is the part I need help with.
ser = serial.Serial('/dev/ttyAMA0', 9600) # Arduino connected to raspberrypi's UART
if first == "TEMP" and checksum == crc32: # Compare against types of readings and check that checksums match
print id + " Temperature: " + reading #
elif first == "HUMI" and checksum == crc32:
print id + " Humidity: " + reading
elif first == "DSDS" and checksum == crc32:
print id + " DS temp: " + reading
elif first == "LDR" and checksum == crc32:
print id + " LDR: " + reading
print "Checksum failed, discarding reading!"
def checkRec(n): # Requests the reading I want, splits it and checks integrity.
ser.flushInput() # Flushing the input to make sure its empty before requesting data
ser.write(n) # Asking arduino something..
answ = ser.readline() # Read until \n
length = len(answ) # Store length of answer for comparison
if length > 25: # If length is over 25, its a double reading so we need a different split and slice
a = re.split('-',answ) # Split eading from arduino: TEMP:1:24.30:1024012001-TEMP:2:23.10:1240120414 #Checksums here are made up
b = a # Store sensor 1 data
c = a # Store sensor 2 data
split1 = re.split(':',b)# Split reading 1
split2 = re.split(':',c)# Split reading 2
first = split1 # Type of sensor reading
id = split1 # Sensor ID
reading = split1 # Sensor reading (concatenated float from arduino)
checksum = int(split1) # Make checksum integer for comparison
crc32 = (binascii.crc32(reading) & 0xffffffff) # Calculate checksum of reading for comparison with checksum sent from arduino
ifIn(first,checksum,crc32,id,reading) # Check integrity and print readings if correct
first2 = split2 # Type of sensor reading nr2
id2 = split2
crc322 = (binascii.crc32(reading2) & 0xffffffff)
else: # If length is under 25, do a single sensor split
split = re.split(':',answ) # Reading has : as separator between type,id,reading,checksum
first = split
id = split
crc32= (binascii.crc32(reading) & 0xffffffff)
January 30th, 2013, 05:54 PM
Assume your reader has neither raspberry pi nor Arduino. You want a more general function. What are the possible inputs? What output do you want for each input? Please describe input in Backus Naur form, if possible, and explain the output concisely. Thanks.
def ifIn(first,checksum,crc32,id,reading,translation = dict(
zip('TEMP HUMI DSDS LDR'.split(),
if checksum != crc32:
message = "Checksum failed, discarding reading!"
elif first in translation:
message = id + ' ' + translation[first] + ': ' + reading
message = first + ' unknown'
[/code] are essential for python code and Makefiles!