2 Layer LX9 Board Design

Hosted forum for UMDK related questions

Moderators: BigEvilCorporation, prophet36

Post Reply
Dan181
Newbie
Posts: 2
Joined: Mon Apr 23, 2018 2:11 pm

2 Layer LX9 Board Design

Post by Dan181 » Sun Jun 17, 2018 12:51 pm

Hi,

I recently (well over the past few months :D) built a UMDK and in the process modified the LX9 board design to be two layer. I can confirm the design works (on my single unit test case at least).

I've attached the KiCAD project for anyone that wants to make use of it.

I had the boards manufactured by JLCPCB and used LCSC for most of the components (I wanted to give the service a go since I might use it for future projects and they offer combined shipping). Boards came out fine and were very cheap - although the gold fingers were missing on the cartridge interface board.

I had to substitute a couple of the parts due to availability. These were a AT24C128C-SSHM-T for the USB flash and W9812G6KH-6 for the RAM both are working fine.
I tried to substitute a AT25SF041-SHD-T for the FPGA flash but this wasn't recognised by the programmer script. I ended up purchasing a pack of M25P40-VMN6 from China (since they're no longer available elsewhere).

There were some issues with the Cypress USB chip not being recognised by the PC (possibly an oscillator issue) and in the end I bought a dev board from Aliexpress and hot-aired off the chip it came with. Amazingly the 'faulty' IC worked when soldered on to the dev board so I'm not sure what the problem was.

If anyone's interested in buying some of the spare boards (I've got 9 of each unused) then please let me know.
Attachments
lx9-r3.7z
(150.24 KiB) Downloaded 24 times

User avatar
prophet36
Very interested
Posts: 234
Joined: Sat Dec 13, 2008 6:58 pm
Location: London, UK
Contact:

Re: 2 Layer LX9 Board Design

Post by prophet36 » Thu Jun 21, 2018 6:46 pm

Hi Dan181, great work. If you still have a board with the AT25SF041-SHD-T soldered to it, I'd be happy to work with you to get it added to the programmer code as a supported part. It should be quite easy to do, if you have actual hardware to test it on.

User avatar
prophet36
Very interested
Posts: 234
Joined: Sat Dec 13, 2008 6:58 pm
Location: London, UK
Contact:

Re: 2 Layer LX9 Board Design

Post by prophet36 » Thu Jun 21, 2018 6:55 pm

Also, the problem with the Cypress chip might well be an oscillator problem. The layout for both the oscillator and the USB signals is quite sensitive, but I have got it working on a home-made two-layer board before - the thing to be sure of is that you don't route the oscillator signals or the USB D+ and D- through any vias, and don't try to route anything underneath those signals (having a GND pour on the opposite side of the board is a good idea).

Dan181
Newbie
Posts: 2
Joined: Mon Apr 23, 2018 2:11 pm

Re: 2 Layer LX9 Board Design

Post by Dan181 » Thu Jun 21, 2018 7:39 pm

I'd love to help unfortunately I only had the one AT25SF041 and pretty sure I binned it after hot airing it off. Meanwhile the board is with my brother ~600miles away (I built it as a birthday present).

I think it was an oscillator problem on the Cypress chip - most of the time it wouldn't produce an output on the CLK test point. I played with the oscillator loading caps but couldn't seem to get anything that worked well.
Maybe the loading or parasitics are close to the limits of the IC on my board and I got lucky with a more tolerant replacement IC... (Equally all the parts we're sourced from China so it's possible they were factory seconds and had inherent issues :)).

Overall the oscillator layout and USB are very similar to the 4-layer design. The oscillator connections are direct, have a ground pour below and are surrounded by a 3.3V pour. The USB is surrounded by the GND pour with the 3.3V pour below. This does have vias though to the Cypress IC but so does the 4-layer design.

I'm happy to send you one of the blank PCBs if you'd like?

User avatar
prophet36
Very interested
Posts: 234
Joined: Sat Dec 13, 2008 6:58 pm
Location: London, UK
Contact:

Re: 2 Layer LX9 Board Design

Post by prophet36 » Thu Jun 21, 2018 8:21 pm

Dan181 wrote:
Thu Jun 21, 2018 7:39 pm
I only had the one AT25SF041 and pretty sure I binned it after hot airing it off.
No worries!
Dan181 wrote:
Thu Jun 21, 2018 7:39 pm
Meanwhile the board is with my brother ~600miles away (I built it as a birthday present).
Wow! What a great brother you are! Mine are shit! :-)
Dan181 wrote:
Thu Jun 21, 2018 7:39 pm
I think it was an oscillator problem on the Cypress chip
I admit I'm not much of an electronic engineer, so I have little clue how to diagnose problems like this, sadly.
Dan181 wrote:
Thu Jun 21, 2018 7:39 pm
I'm happy to send you one of the blank PCBs if you'd like?
I doubt I'd have time to play with it, so I'll skip. Thanks for the offer though!

Chris

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests