Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 7 of 7

Thread: Custom PCB with ethernet-kit clone section.

  1. #1
    Junior Member
    Join Date
    Jun 2021
    Posts
    4

    Custom PCB with ethernet-kit clone section.

    Hi,

    I'm trying to make a custom PCB that will be used for a lighting control module based on Teensy 4.1 and building onto the board the circuitry from an OCTOWS2811 and Ethernet kit module.
    I'm happy with the octo section, its just the ethernet kit module has several lines that are wiggling around on the bottom of the board.

    I imagine these wiggles are to make sure the T+/T- and R+/R- lines are as close in length to each other as possible?
    I've been trying to match the shape (using EasyEDA), and I'm getting close was wondering if it matters that the T-pair and R-pair are different lengths?
    I have the T+ and T- in at 25.296 and 25.286mm (0.01mm diff), the R+ and R- at 10.727mm and 10.725mm, does it matter that they are so different?

    I'm planning on using the same 6x1 cable that is in the kit, rather than routing the 6 lines directly from the teensy to the ethernet section.
    I could perhaps integrate these into the PCB too, any advice welcome!

    Also anything else I should look out for in this section?
    I'm adding 12v power lines (with a 12v > 5v convertor for teensy) to a separate section of the board, but these are going to be isolated from the teensy and octo and ethernet sections.

    Thanks in advance!

    Click image for larger version. 

Name:	Screenshot 2021-06-01 at 15.49.07.jpg 
Views:	16 
Size:	116.6 KB 
ID:	24958

  2. #2
    Member
    Join Date
    Feb 2017
    Location
    Chicago, IL
    Posts
    36
    As TX and RX are independent from a signaling/functional perspective, I don't think their relative lengths matter. I have a custom board with a Teensy 4.1 and Ethernet amongst other things (designed in EasyEDA too), and the TX / RX lines differ from each other by 8.059mm. RX+/- have an 0.008mm difference (best I could get with a mini Lombard Street design) and TX+/- have an 0.001mm difference. Everything functions without issue.

  3. #3
    Junior Member
    Join Date
    Jun 2021
    Posts
    4
    Thats great, thanks for the info!
    I figured as much for the different TX/RX lengths, looking at my layout now, I'm going to experiment with removing the cable and doing everything on the pcb. What can possibly go wrong eh?

  4. #4
    Member
    Join Date
    Feb 2017
    Location
    Chicago, IL
    Posts
    36
    Yeah, what indeed could go wrong? One thing, if you currently use 2.54mm headers to attach the Teensy to the PCB, the Ethernet ones are smaller pitch and size, so just ensure the ethernet male/female header combo has sufficient reach from Teensy to the board. I also routed all other traces away from passing under the Tx / Rx lines as best I could, I read this was a good practice, but I still have pin 20 (carrying parallel data to a TFT) crossing under the Tx lines on the lower layer, with no apparent adverse effects. All in all, I basically kept the +/- lines physically close on the board and also in length, routed other signals away, and everything worked fine!

    Click image for larger version. 

Name:	Image1.jpg 
Views:	18 
Size:	158.7 KB 
ID:	24962

  5. #5
    Junior Member
    Join Date
    Jun 2021
    Posts
    4
    Great advice!
    I had a teensy+ethernet kit infant of me and have been working round the 2.54 v 2 mm spacing on the two headers, not a problem design wise, but surprisingly painful finding 2mm parts (with a short lead time at least!) I finished my board up and ordered last night, I also was able to keep the TX+RX lines away from all the others, managing to have an exact match in lengths for both pairs (well as far as EasyEDA is accurate!).
    Due to the other components on the board I was able to space out the components a bit, and have room for improving this prototype and make other additions at a later date. Quite happy with the final design, which will be with a black pcb finish. Though it will be hidden away in a 1U rack box!

    Click image for larger version. 

Name:	Screenshot 2021-06-01 at 23.03.37.jpg 
Views:	15 
Size:	73.3 KB 
ID:	24963

  6. #6
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    24,485
    Quote Originally Posted by nebulus View Post
    but surprisingly painful finding 2mm parts (with a short lead time at least!)
    PJRC has plenty of these in stock.

    https://www.pjrc.com/store/header_socket_3x2.html

  7. #7
    Junior Member
    Join Date
    Jun 2021
    Posts
    4
    Quote Originally Posted by PaulStoffregen View Post
    PJRC has plenty of these in stock.

    https://www.pjrc.com/store/header_socket_3x2.html
    Thats great to know! Unfortunately I'm on the wrong side of the Atlantic to make getting these from you quick I suspect...
    Are these (the long male pins) available from Digikey, I'm putting an order together to cover a load of other parts can't quite find them on there right now.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •