#!/usr/bin/python3
# Unpack the dht11 data which are packed into 32bit words into individual bits
# and write these to a file
# The file can then be plotted with gnuplot
# Copyright (c) U. Raich 10.3.2020
# This program was written for the course on embedded systems at the
# University of Cape Coast, Ghana
# It is released under GPL
#

# open the file with the packed data which must be named: "dht11Packed.dat"

import sys

try:
    fd_r = open("dht11.txt","r")
except:
    print("Could not open the file 'dht11Packed.dat' for reading, giving up ...")
    sys.exit()

bits=[]
bitNo=0
bitOn = False
bitLength = 0

for i in range(32):
    d=int(fd_r.readline(),base=16)
    # print("value read: %08x"%d)
    mask = 0x80000000
    for j in range(32):
        if d & mask:
            if not bitOn:
                # here we start a data bit pulse 
                bitOn=True
                bitLength=1
            else:
                # calculate the length of the data pulse 
                bitLength += 1            
        else:
            if bitOn:
                # this is the end of the data pulse 
                bits.append(bitLength)
                bitNo += 1
                # print("bit length of bit %d: %d"%(bitNo,bitLength))
                bitLength=0
                bitOn=False
                
        mask = mask >> 1

fd_r.close()

if bitNo != 40:
    print("Something is wrong with the protocol")
    sys.exit(-1)

decodedData=[]
for i in range(5):
    d=0
    for j in range(8):
        # print(bits[i*8+j])
        if bits[i*8+j] > 10:
            d |= 1
        if j < 7:
            d=d<<1;
        # print("%2x"%d)
    decodedData.append(d)

checksum = 0
for i in range(4):
    checksum += decodedData[i]
if checksum != decodedData[4]:
    print("Chechsum error: expected: 0x%02x but found: 0x%02x"%(decodedData[4],checksum))
temperature = decodedData[2]
humidity = decodedData[0]
print("temperature: %d °C, humidity: %d %%"%(temperature,humidity))