Temp sensors register 3920 intermittently

[TJF1960]

Hello,

I have 8 temp sensors purchased from Mouser pn DS18B20+ which I selected because the specs indicated they were more accurate than some of the others. The wiring for the most part is star configuration which I know is not the best from what I have read. The approximate distances are 2ft, 4ft, 5ft, 6ft 10ft, 15ft, 20ft and 40ft and I used cat5 cable for all runs.

They all work fine most of the time. However every once in a while, maybe a couple of times a week one randomly will show 3920 for a few seconds then return to normal. Every one of them at one time or another has done this. Is this a known problem, have other experienced it?

I have installed a 4.7k ohm pull resistor up from Vdd to DQ at the sensor at the longest run. I also added one at the second longest run as well.

The board is rev 2.0.2 with firmware v03.01.06 and I modified the board per CAI to supply 5v to the temp sensors instead of the 3.2v.

Is it ok to add a pull up at every sensor? If ok would that be a possible solution or am I dealing with another issue?

Thanks,
Tim

 

[CAI_Support]

Hi Tim,

The 2.0.2 board does not work as well as 2.2.2 board, due to its hardware differences. On the 2.2.2 board, the 1-wire bus is powered by 5V, but 2.0.2 board powered by 3V. That cause a lot problem for the 1-wire bus. If really like to keep using the 2.0.2 board with your temp sensors, you may consider replace the 3.0 voltaage regulator with 3.3V, part number TC1262-3.3

2.2.2 board also have hardware pull up chip. there is no way to add that to the 2.0.2 board.

 

[TJF1960]

I just wanted to let you know that after replacing the old 2.0.2 board with the new 2.2.2 board I have not had (knock on wood) any temp sensor malfunctions like before. I would get an email every couple of days with the old board when the temp reading jumped to 392 from anyone of the 8 temp sensors (and it was never the same sensor that errored, was always random). Haven't had 1 in the last month!
Thanks,
Tim

 

[CAI_Support]

Thanks, Tim.  Hardware 2.2.2 has improvide hardware design for 1-wire bus. 1-wire sensors are working much reliable on the hardware rev 2.2.2 boards.