Long reading time / measurement delay

[pedroluisneves]

Dear all,

Is there a reason for waiting 1 second while performing a temperature measurement?
self._owReset(); self._owWrite(0xcc) self._owWrite(0x44) time.sleep(0.01) self._owReset(); self._owWrite(0xcc) self._owWrite(0xbe)

I just reduced it to 10 milliseconds and observed that my read value seams from while ago, not reflecting the most recent temperature change.
If measure needs time to be performed, is there a way of checking new measure is done from the hardware?

[jaka]

1 second is just safe value. In the sensor datasheet (Table 2) the following is given:

RESOLUTION (BITS)	MAX CONVERSION TIME
9	93.75ms (tCONV/8)
10	187.5ms (tCONV/4)
11	375ms (tCONV/2)
12	750ms (tCONV)

Reading value too soon might result in wrong value.

The master can issue read time slots after the Convert T command and the DS18B20 will respond by transmitting a 0 while the temperature conversion is in progress and a 1 when the conversion is done.

Pseudo code after self._owWrite(0x44) might be:

while:
self.uart.write(0xff)
r = self.uart.read(1)
if r == 0xff: break #done

I haven't tested this yet.

[pedroluisneves]

Thank you for the feedback, I will try as post back the results.