Atom 2k18 ?

discussion of games, software, hardware & emulators relating to the Acorn Atom and Acorn System machines.
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hoglet
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Re: Atom 2k18 ?

Post by hoglet » Tue Apr 09, 2019 8:13 pm

That looks great Roland, definitely the right thing to do on a board this size.

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Re: Atom 2k18 ?

Post by myelin » Tue Apr 09, 2019 8:25 pm

What's the purpose of the split in the ground plane? (I assume purple = In2.Cu / bottom inner layer.)
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Re: Atom 2k18 ?

Post by hoglet » Tue Apr 09, 2019 8:47 pm

myelin wrote:
Tue Apr 09, 2019 8:25 pm
What's the purpose of the split in the ground plane? (I assume purple = In2.Cu / bottom inner layer.)
I think the purple layer is is power plane, split between 3.3V and 5V.

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Re: Atom 2k18 ?

Post by fordp » Tue Apr 09, 2019 10:02 pm

I am not and expert but would like to look at the KiCad design. I hope to build on this project with one of my own I have been planning. I saw in the past that Hoglet ( Dave) made a homebrew Atom keyboard is that design available. It would be great to have an Atom design with all modern easy to get parts.
Last edited by fordp on Tue Apr 09, 2019 10:06 pm, edited 2 times in total.
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Re: Atom 2k18 ?

Post by roland » Wed Apr 10, 2019 6:01 am

hoglet wrote:
Tue Apr 09, 2019 8:47 pm
myelin wrote:
Tue Apr 09, 2019 8:25 pm
What's the purpose of the split in the ground plane? (I assume purple = In2.Cu / bottom inner layer.)
I think the purple layer is is power plane, split between 3.3V and 5V.
That is correct. Purple is 3.3 and 5V.

As soon as we know that the board works then I will release the KiCad files and every body who wants to modify it can use them.
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Re: Atom 2k18 ?

Post by fordp » Wed Apr 10, 2019 6:54 am

I may be imagining things but was there a design for a perspex (acrylic) laser cut case for an atom in the past?
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Re: Atom 2k18 ?

Post by bprosman » Wed Apr 10, 2019 9:28 am

Not that I am aware off. I'm interested in DIY cases as well. As I have some (original) boards without cases as well .

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Re: Atom 2k18 ?

Post by roland » Wed Apr 10, 2019 8:14 pm

Almost my final design of the pcb. I just need to add some info of the jumpers on the silk screen.....
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Re: Atom 2k18 ?

Post by fordp » Thu Apr 11, 2019 6:47 am

My only comment is that I am surprised the 3.3V plane does not run under the entirety of the FPGA board as there is nothing running at 5 V there. The highest speed and most critical part is the fast SRAM right under that board.
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Re: Atom 2k18 ?

Post by roland » Thu Apr 11, 2019 10:18 am

The FPGA board is powered with 5V through the two schottky diodes. The ground plane "covers" the fast SRAM.
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Re: Atom 2k18 ?

Post by hoglet » Sat Apr 13, 2019 12:38 pm

Roland,

I've just been re-checking my Beeb 1MHz Bus Adapter board before sending it off to be made.

I thought it would be useful to check against the FPGA Modile footprint you posted here:
viewtopic.php?f=3&t=16643&p=232808#p232848

I'm comparing your footprint to my physical FPGA module, and there are some discrepancies.

1. Spacing of 2x20 connectors

- On my module, if you measure from the inside pin of one connector to the inside pin of the other connector, it measures exactly 1.6 inches.
- On your footprint, that same dimension is 1.55 inches. That's enough that it would not fit.

2. Offset to the 2x6 connector

- This might also be out slightly. But it's difficult to tell until (1) is fixed.

I believe the spacing of the these connectors should be the same as the DE0-Nano. Here's a technical drawing of that:
de0-nano_dimm2.pdf
(42.08 KiB) Downloaded 3 times
The same measurement from there is (44.96-4.19) = 40.77mm = 1.605 inches.

I'm wondering if you just measured this wrongly, or if the design itself has changed.

Can you carefully re-measure your module?

Dave

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Re: Atom 2k18 ?

Post by roland » Sat Apr 13, 2019 5:46 pm

Thanks for noticing me. I bought a schuifmaat to measure the exact distances on my board. It seems you're right and I corrected my footprint. I got the distances by "guessing" and printing the footprint but my printer is not accurate enough (I had the same issue with the fast SRAM footprint). Now it should be good.

I have attached the new footprint so you can double check it.

About the schuifmaat .... I tried to find the correct English word for it and the Internet came up with:
  • caliper
  • caliper gauge
  • marking gauge
  • vernier caliper
  • schuifmaat.jpg
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Re: Atom 2k18 ?

Post by -B- » Sat Apr 13, 2019 5:57 pm

I have always known them as calipers. I have a plastic set that came free with an industry magazine!
Some people I used to work with, who will remain nameless, called them verniers, which is wrong.
The calipers have a vernier scale.
So I guess it’s calipers or vernier calipers.

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Re: Atom 2k18 ?

Post by hoglet » Sat Apr 13, 2019 6:13 pm

roland wrote:
Sat Apr 13, 2019 5:46 pm
I have attached the new footprint so you can double check it.
Phew! I had a horrible feeling that you might have already sent the boards off.

I've had too much wine this evening to make a reliable measurement, so I'll check tomorrow. :D

My printer does seem to be quite accurate, so I'll print it out as well.

Dave

P.S. I would call that measuring device a caliper.
Last edited by hoglet on Sat Apr 13, 2019 6:13 pm, edited 2 times in total.

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Re: Atom 2k18 ?

Post by roland » Sat Apr 13, 2019 6:19 pm

hoglet wrote:
Sat Apr 13, 2019 6:13 pm
Phew! I had a horrible feeling that you might have already sent the boards off.
I've had too much wine this evening to make a reliable measurement, so I'll check tomorrow. :D
I assume you didn't drink that wine because of that horrible feeling :lol:

I'll wait with ordering the boards. By placing the connectors not in a 90˚ angle on the board it might have fitted anyway. The deviation was only a few millimetres. Have a nice evening and enjoy your wine...
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Re: Atom 2k18 ?

Post by hoglet » Sun Apr 14, 2019 7:18 am

roland wrote:
Sat Apr 13, 2019 6:19 pm
I'll wait with ordering the boards. By placing the connectors not in a 90˚ angle on the board it might have fitted anyway. The deviation was only a few millimetres. Have a nice evening and enjoy your wine...
The main connectors are now perfect.

The extra 2x6 pin connector still seems to be out slightly.

My measurements (between the closest pins) were:
- horizontally offset by 0.175"
- vertically offset by 0.25"

Yours are currently:
- horizontally offset by 0.2024"
- vertically offset by 0.2378
(what grid were you using???)

Again, on printing (and turning the page over), I do see enough of a shift to worry me (mainly in the horizontal direction)

Dave
Last edited by hoglet on Sun Apr 14, 2019 7:25 am, edited 3 times in total.

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Re: Atom 2k18 ?

Post by hoglet » Sun Apr 14, 2019 7:26 am

However, measuring yet again.

I think your vertical dimension may be correct though. Using a ruler marked with 0.25 inch divisions, I can see the vertical dimension is now slightly less than 0.25 of an inch.

The dog is squeaking for a walk, but I'll come back to this in a couple of hours.

Dave

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Re: Atom 2k18 ?

Post by daveejhitchins » Sun Apr 14, 2019 7:36 am

I always find it handy to have a rule with 10ths of an inch - I have a 6" and 12" rule with a 10th scale. They're getting harder to find but should be readily available in the US (?).

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Re: Atom 2k18 ?

Post by hoglet » Sun Apr 14, 2019 9:37 am

Thanks Dave. Yes, I have one of these as well.

I think I'm going to settle with my original measurements (between the closest pins) of:
- horizontally offset by 0.175"
- vertically offset by 0.25"

I'm using 1mm holes, so there is a bit of play when soldering the headers in. What I usually do is to fit the headers into the FPGA board, mate the boards, then solder all the end pins, to keep everything nicely aligned.

Roland, your holes are 0.762mm and the pads are 1.524mm. This seems a too small for normal 0.1" square header. The pin size is usually 0.025" (0.635mm), which has a diagonal of 0.035" (0.898mm). You really need 1mm holes and 1.7mm pads. You can still get a 10mil trace between the pins, with 10mil spacing each side.

(Also, JLCPCB's tolerance on finished hole diameter is +- 0.08mm).

It's worth checking all your hole sizes carefully. This is where errors often creep in, because they are easily overlooked.

Dave
Last edited by hoglet on Sun Apr 14, 2019 9:43 am, edited 5 times in total.

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Re: Atom 2k18 ?

Post by roland » Sun Apr 14, 2019 12:49 pm

Thanks Dave, I really appreciate your support!

I have moved the 2x6 pin header and I also enlarged the holes. They were 1mm but after updating the footprint they were reset to 0.8mm. I now updated the footprint now with 1mm holes.

My final design is in the attached file.
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Re: Atom 2k18 ?

Post by hoglet » Sun Apr 14, 2019 1:17 pm

Can you let me have some gerber files? They are much easier to review.

Where are you with design rule checks in the PCB layout program? All passing?

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Re: Atom 2k18 ?

Post by roland » Sun Apr 14, 2019 5:56 pm

hoglet wrote:
Sun Apr 14, 2019 1:17 pm
Where are you with design rule checks in the PCB layout program? All passing?
Yes, before I started the design I set up the design rules with the specs of MakePCB. The specs of JCLPCB are within those specs and the DRC runs without any errors, warnings and unconnected pads.
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Re: Atom 2k18 ?

Post by roland » Wed Apr 17, 2019 9:23 pm

If there are no more comments I am going to order the pcb's this weekend.
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Re: Atom 2k18 ?

Post by roland » Sun Apr 21, 2019 10:55 am

I had one comment myself: the keyboard connector had VCC and GND swapped compared to the Atom 2k15 design. That would make the keyboard connectors incompatible. After fixing this I just closed my eyes, created the gerber files and uploaded the stuff to JCLPCB. I expect them somewhere next week.
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Re: Atom 2k18 ?

Post by fordp » Sun Apr 21, 2019 5:59 pm

Let's see what turns up. I am looking forward to this.
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Re: Atom 2k18 ?

Post by roland » Thu Apr 25, 2019 3:11 pm

Today I got a message that the boards are on their way to me :D

Did we also mention that we already have found the first bugs in the pcb? The footprint of the FPGA module has some pin numbers swapped so this will become a more realistic Atom with cut tracks, additional solder joints and wire bridges :mrgreen:
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Re: Atom 2k18 ?

Post by bprosman » Mon Apr 29, 2019 4:51 pm

Isnt the FPGA known for its flexibility to swap signals ? :lol:
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Re: Atom 2k18 ?

Post by hoglet » Mon Apr 29, 2019 5:01 pm

bprosman wrote:
Mon Apr 29, 2019 4:51 pm
Isnt the FPGA known for its flexibility to swap signals ? :lol:
You can't swap power signals :(

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Re: Atom 2k18 ?

Post by roland » Tue Apr 30, 2019 9:33 pm

I have started to solder the most basic components on the board to make it display the text ACORN ATOM. Just in case that the boards have a fault that might them make unusable (then I did not spoil to much components).

First of all, I corrected the errors in the FPGA module socket:
IMG_3567.JPG
I removed pin 14 of the left connector and made a bridge between pin 14 and 15 on the board. But now that I write it down I realize that this is not the correct fix ](*,) I have to remove pin 15 (the real 3.3V pin) and connect pins 15 and 16 on the board. So I need to remove the connector and start over again. [ Here were some words that could have made an admin to remove my account ]

The other correction is correct: remove pins 87 and 88, remove the solder pad on pin 88 with a drill (by hand!) and bend out pin 88 of the header so the resistor can be connected to that pin:
IMG_3564.JPG
IMG_3566.JPG
IMG_3568.JPG
And after checking the power I dared to plug in the FPGA module and have a test running:
IMG_3569.JPG
So tomorrow I will start with replacing the connector and programming the eeprom and FPGA module and then we will see what happens ....
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Re: Atom 2k18 ?

Post by roland » Wed May 01, 2019 9:18 pm

The ROM is programmed ....
The RAM is inserted ....
The FPGA is configured ....

And this is the result:
IMG_3572.JPG
It's not exactly "ACORN ATOM" but it is also not completely dead. I didn't check any signals yet because it took me quite a while to figure out what type of SPI ROM there is on my board. The schematic says M25P80, the manual says W25Q64 but it turns out that my board has a W25Q32 on board.

It will be a tough job to find out what's going on or not ....
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