On Thu, 27 Nov 2014, Gareth France wrote: > I really don't understand what you have done here. > >>>> > >>F3 01 90 B7 - 42.79 - 0x90b7 & 0x7fff => 0x10b7 => 4279 decimal > >>>> > >>F3 01 97 78 - 60.08 - 0x9778 & 0x7fff => 0x1778 => 6008 decimal
The two bytes we're interested in (0x90b7) together give us 16 bits of information. This is split into two, 1-bit for one value (true or false) and 15-bits for a measurement value (zero to 32k). 0x90b7 1001000010110111 (binary) When we split it, the two parts are: 1 and 001000010110111 We can pass these to Python to convert from binary to decimal; the '0b' prefix means binary, just like '0x' means hexadecimal: python -c 'print 0b1, 0b001000010110111' 1 4279 The first value is actually a boolean (True/False) and is inverted, and the second is multipled by 100: python -c 'print bool(not 0b1), 0.01*0b001000010110111' False 42.79 We don't need to go to the binary representation at all, we can split the field using bitwise arithmatic AND (&) and right shift (>>) : https://en.wikipedia.org/wiki/Bitwise_operation#AND https://en.wikipedia.org/wiki/Bitwise_operation#Arithmetic_shift python -c 'print bool(not 0x90b7 >> 15), 0.01 * (0x90b7 & 0x7fff)' False 42.79 We can test this another result too: python -c 'print bool(not 0x9778 >> 15), 0.01 * (0x9778 & 0x7fff)' False 60.08 python -c 'print bool(not 0x48db >> 15), 0.01 * (0x48db & 0x7fff)' True 186.51 In this case, this is above >99.99, which the new meter shows as '99.99' so we need to cap it with the minimum function: python -c 'print bool(~0x48db>>15),min(99.99,0.01*(0x48db&0x7fff))' True 99.99 and just to re-check with the others: python -c 'print bool(not 0x9778>>15),min(99.99,0.01*(0x9778&0x7fff))' False 60.08 -Paul -- ubuntu-uk@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-uk https://wiki.ubuntu.com/UKTeam/
