ser.read(1)
data = ser.read(4)
ser.readline()
vF, = struct.unpack('<f', data)
vSf = float(vS)
diff = vF - vSf
if diff < 0:
    diff = 0 - diff
if diff < 1e-11:
    diff = 0
print('Str:', vSf, ' Fl: ', vF, ' Dif:', diff)
Отправка данных типа float из Arduino в Python