Custom PCB with ethernet-kit clone section.

nebulus

New member
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!

Screenshot 2021-06-01 at 15.49.07.jpg
 
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.
 
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?
 
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!

Image1.jpg
 
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!

Screenshot 2021-06-01 at 23.03.37.jpg
 
Hello, I was also designing an ethernet kit but this one is the Abracon ARJE-0032 that is USB stack combined that way i can break out the ethernet and the USB. This is the same type magjack as the one Paul uses but the dot notation on the back mags are different. Is this going to be a problem or are they all acceptable. The small red circles are the dot notation which is different from Pauls.
Thanks very much,
Marathonman
Teensy Breakout RJ45 and USB.PNG
Teensy Breakout RJ45 and USB front view.PNG
Magjack Schematic.PNG
 
Only whether the dots are on the same side, or on different sides of the same pair, matters. This means yes, you can use ARJE-0032, as long as you take care about the pinout on your own board (that is, even the pin numbering on the chip/pcb side differ).
 
Thanks and YES!, I accounted for that in the pinout since pin 1 and 6 are CT. I am curious about the LED's though as Paul did not use resistors on his MJ kit.
 
Only one of the LEDs is used. If you look at the Teensy 4.1 schematic, on the right side, ethernet connects to DP83825 PHY. You'll also notice R3 (150 ohm) connected between the PHY LED0 pin and the LED pin. In other words, that resistor is included on the Teensy 4.1 itself, not on the breakout board.
 
Only one of the LEDs is used. If you look at the Teensy 4.1 schematic, on the right side, ethernet connects to DP83825 PHY. You'll also notice R3 (150 ohm) connected between the PHY LED0 pin and the LED pin. In other words, that resistor is included on the Teensy 4.1 itself, not on the breakout board.

WOW i missed that. Well that was forward thinking on Paul's part LOL! Not to many people do that and certainly not Corporate America or Multinational Corporations as they are cheep as hell and profit above everything.
Thanks so much for pointing that resistor out as I did omit that in the board anyways. cool and thanks!
With the ARJE-0032 the green and orange are together as one unit yet 180 from each other.

Defrag; Thanks you very much!

Regards,
Marathonman
 
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Now finding a 12 pin ribbon cable that doesn't cost an arm and a leg is a different story in these times of man made epidemic and shortages. Seems everyone is price gouging which is illegal in a so called plandemic, I mean pandemic, How silly of me. LOL!
If anyone knows of a supplier of small quantity 12 pin ribbon cable please by all means speak up.
 
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