20-09-2016, 01:01
(19-09-2016, 18:03)hornychz Wrote: That is the question, if he only wants to bother us?
My dear friend, I liked that!I have just followed what is said in the P82B715 datasheet.
(19-09-2016, 15:59)hornychz Wrote: ...
2) this more important for me: when I study P82B715 datasheet to manage the Rx values, I found Fig. 9 in the chapter 8.2 = Quick design-in point-to-point/multi-point information for 5 V bus. They recommend to put resistance 4.7kOhm on each I2C-bus (SDA and SCL) and on each end of the cable resistance 470Ohm (buffered bus, LSDA, LSCL). It would be satisfactory up to long 30 or maybe 50m of UTP cable Cat5e. Do you agree, please, with this idea?
...
My installation will have 8 m of outdoor UTP Cat5e cable ...
Regards
Yes, I agree! According to the datasheet, the pull-up resistors at both sides of the SDA and SCL bus, should be calculated according to cable length and type.
In your case, with a UTP cable of just 8 meters it's possible that it will work just with the default 4.7K resistors already installed on the TX unit (R9 and R10) and without the corresponding R1 and R2 resistors on the Soil / Leaf interface (mine is working that way with 5 meters of UTP cable).
The reason why on the Soil / Leaf interface the R1 and R2 resistors are the only through the hole parts, is exactly to allow the user to install the resistors with the value that best fit their needs in function to cable length we want to use.