(SOLVED)Temp probe null

First of all apologize for my English is not my native tongue , I live in Argentina and speak Spanish .

I just received my Brewpi-spark and have a drawback.

Do not connect still with raspberry I’m just working with the screen test preinstalled, version 0.4.3.

What happens is this , I have 3 temperature probes if connect separately read correctly , when I connect together one of the 3 appears the word null, disconnect any of the other two who read well and again recognize that before was null .

I 'm not putting the pull down resistor because I understand that is integrated into the i2c bus .

some clues?, tanks in advance.

Did you buy your temperature probes from us?

Is there a sensor that causes more problems than the other 2 when connected?

no probes are not of you , were purchased several years ago by ebay.

It is indistinct, do with any of them , always when a third sensor, works perfectly with two sensors connected .

tanks Elco

My guess is that your sensors have a pull up resistor in each sensor. If you connect multiple, the combined pull up on the bus becomes too high and the master cannot pull down the bus.

You can measure the resistance of a sensor between 5v and data to confirm.

There should only be one 4k7 pull up resistor on the bus and this is already provided by the bus master in the BrewPi Spark.

Thanks, I 'm trying to get some DS18B20 unencapsulated to test well, tonight I test and comment the result

EUREKA … Elco were right probe with three DS18B20 unencapsulated and everything works properly.
Thanks for the help so far away is invaluable to have this quick and accurate diagnosis .

I’d like to add (for the people that come here from Google) that I had the same issue (probe returning null) when I swapped out my eBay bought ds18b20 with Brewpi’s 1/2" probes). Turned out I had forgot to install arduino-core on my raspi which caused manual firmware updates to the Arduino to not succesfully complete; it was still looking for my old sensor. I installed arduino-core to the raspi, wiped the Arduino with 2.10 with a clean config and all was well again.