Ethernet PCB Devolopment Teensy 4.1

[cjaeck]

Hi there,

I designed a PCB-Board to transfer informations from a USB-Scanner via MQTT to a Server. At first glance, this is not a complex task.
But: I gradually realized that Ethernet is not as trivial as I thought it was.
As a basis for my PCB design I used the Ethernet module available on the PJRC site:
https://www.pjrc.com/store/ethernet_kit.html
Unfortunately, my design is not working and I just can't find the problem. Hopefully there are people here on the forum who are pro's in the subject and can help me! Regarding to my PCB-Design: I know that I should not have placed a ground area under the RJ45 jack. Furthermore I know that it is very suboptimal that the VCC line runs directly underneath the RJ45 jack.
I have attached the PBC design, the schematic and the datasheet of the used RJ45 jack (Sorry, its in german).

I am very happy about help! Thanks a lot in advance!

Chris

 

[PaulStoffregen]

Which ethernet magjack did you solder to your PCB?

Design looks correct for Cetus J1B12111CCD or Link-PP LPJ4012AHNL (the 2 possible parts used on the ethernet kit - PJRC has used both of these parts over the last 2 years - the PCB we ship today has both parts numbers printed).

But your message has a datasheet for Weidmüller M100_T1D_32E4N, which has different pinout.

 

[PaulStoffregen]

Ethernet magjacks have many different pinouts. There is no official or de-facto standard.

During Teensy 4.1 development, we used UDE RB1-125BAG1A, which has a completely different pinout from Cetus and Weidmüller.

https://oshpark.com/shared_projects/5epewE3O

But the UDE part was unavailable when Teensy 4.1 started shipping, so the PCB was redesigned for the Cetus part.

 

[cjaeck]

Oh wow...that's not fair! I've spent hours for finding the problem and you are solving the problem in minutes.
Thanks a lot Paul! So my fault was the pin-mapping.
One more questing: In our case T+ of the magjack has to be connected to T+ of the Teensy-Board? Because in UART its Tx to RX.

 

[cjaeck]

Hello again, I have another question:
In your old version with UDE magjack you've implemented 4 capacitors. What are these for? And why did you reduce the capacitor number in the newer version?

 

[PaulStoffregen]

The old PCB has 3 capacitors and 1 resistor. But it's really 2 pairs of parts in parallel.

The ones joining the grounds were completely unnecessary.

The other pair became just a single 0.1uF in the final version. But early on, it wasn't known (at least to me) whether a single capacitor would be good enough, or if a large cap and small higher frequency one would be needed.


And FWIW, I did spend several minutes following the wires on your PCB and coming back again and again to the conclusion it really ought to work. Wasn't until I closed the windows with copies of the images and a copy of the ethernet kit's PCB that I saw the datasheet with a different part number.