Cross-Talk and Ground Planes « LeafLabs Garden

LeafLabs Garden » Support » Maple Hardware Support

Cross-Talk and Ground Planes

(26 posts) (5 voices)

Started 5 years ago by Silntknight
Latest reply from Silntknight

« Previous 12

Silntknight
Moderator

Gbulmer, thanks for the idea about using cut-off leads. That should be better and easier. Also, I already have the copper boards (double-sided). I plan to print all my layouts to scale and outline it with a trace the runs just outside the board to line everything up. Then, before I etch it, I will drill 4 guide holes to ensure everything is in place. I'd like to try doing as much as I can myself because (not to try to sound like an educator but) this is supposed to be an educational experience. Plus, working with Ferric Chloride should be exciting. I have adequate facilities for handling chemicals (school...).
Hopefully for hand routing all of it, this wasn't too bad. I might change the design again to move the PWM outputs closer to the opto, but I'll see. As it is, does it look better? Moving stuff offboard really helped.

Mbolivar, good to know that it is something that will be looked at. I understand the focus on the Maple hardware. If fact, I like that. Support here is great, so I like that you are all working on the hardware aspect to make the boards even better.

Soundcyst, thanks for the link. Multiple copies would be mostly useless because I only ordered enough parts for one copy with 1 or 2 spare parts. The prices are a little high for my project. Right now I have maybe $80 left to work with until I find more donations/sponsors.

On that note, I was able to get 8 fuel injectors (with two fuel rails) donated. That saved me at least $15. Now I just need a pump, ignition coil (or two), and an O2 sensor.

Posted 5 years ago #
gbulmer
Moderator

soundcyst - Thank you very much.

I've never heard of http://pcb.laen.org before.
At $5 international shipping, it is still very, very competitive for small boards.
We were thinking of making an adapter for LGA chips, but the price was putting us off.

I'll likely give them a go! Thanks again.

Posted 5 years ago #
Silntknight
Moderator

I have some new images:
http://i1221.photobucket.com/albums/dd470/Hari_Ganti/ECUShieldTopLayer.jpg
http://i1221.photobucket.com/albums/dd470/Hari_Ganti/ECUShieldBottomLayer.jpg

Finally, I accomplished my goal of making everything fit in the Maple form factor. The answer, obviously, was to take stuff off the board. Anyway, this should look much better now. The signals travel MUCH less distance than they used to. I also have three isolated ground planes. One for the PWM outputs, along with all the associated components, one for the digital switch inputs, and one for all the analog inputs.

Posted 5 years ago #
gbulmer
Moderator

Then, before I etch it, I will drill 4 guide holes to ensure everything is in place.

I realise this might sound a bit patronising, but is isn't intended to be.

Try to ensure the 4 guide holes are asymmetric, so that it isn't possible to make a mistake.
It is quite normal to make holes in a nice symmetric pattern, which leaves confusion.
Edit: make the guide holes small, as they effect the limit of your alignment error.

Also, put some text on both sides.
Olimex insist on this so that they can instantly see the photomasks are the right way up.

Edit: I don't know what PCB package you used, but people who design PCB's for a living suggest using a hatched copper pour (e.g. the large areas of copper ground plane).
This reproduces better when you make the mask (large areas of black seem to produce less dense blacks, than hatched areas on laser printers).
More importantly, the etching process tends to be is more uniform, i.e. tracks are more uniformly etched when the large copper areas are hatched.

You might try persulphate instead of ferric chloride. Ferric chloride stains very-near-permanently, and I believe is is more hazardous to dispose of.

Posted 5 years ago #
Silntknight
Moderator

Don't worry about being patronizing. It's better to assume nothing. I'll make them asymmetric AND use a mark to indicate the alignment corner, like most IC devices.

About putting text on both sides, I like it. If I can read it, it is the right way up.

Edit: I don't know what PCB package you used, but people who design PCB's for a living suggest using a hatched copper pour (e.g. the large areas of copper ground plane).
This reproduces better when you make the mask (large areas of black seem to produce less dense blacks, than hatched areas on laser printers).
More importantly, the etching process tends to be is more uniform, i.e. tracks are more uniformly etched when the large copper areas are hatched.

I'm really confused here. I used ExpressPCB. Hatched copper pour? Do you mean make the large areas a series of really close lines?

Thanks for the advice on chemicals. I'll try to find some persulfate.
Aside: I've noticed you spell using Commonwealth spelling. It's interesting. I used to live in Canada, so whenever I visit I always revert to Commonwealth spelling.

Posted 5 years ago #
gbulmer
Moderator

Edit: I don't know what PCB package you used, but people who design PCB's for a living suggest using a hatched copper pour (e.g. the large areas of copper ground plane).
This reproduces better when you make the mask (large areas of black seem to produce less dense blacks, than hatched areas on laser printers).
More importantly, the etching process tends to be is more uniform, i.e. tracks are more uniformly etched when the large copper areas are hatched.

I'm really confused here. I used ExpressPCB. Hatched copper pour? Do you mean make the large areas a series of really close lines?

Yes. This shows a picture of a (probably) ground plane which looks like two sets of lines drawn in orthogonal directions.
http://commons.wikimedia.org/wiki/File:PCB_copper_pour_hatch_filled.png
The holes make a checkered pattern. It doesn't need to be at 45 degrees to the board.
http://wiki.altium.com/display/ADOH/Polygon+Pours+and+Copper+Regions

In Eagle, it is the 'Polygon Pour' attribute of the polygon used to make the ground plane area. So once the area is drawn, the value of 'Polygon Pour' is set to 'hatched' and a couple of attributes set the width of pattern.

Thanks for the advice on chemicals. I'll try to find some persulfate.

Definitely check that it is easier to dispose of in your area. We were surprised it was different here, but it seems to make a difference.

Aside: I've noticed you spell using Commonwealth spelling. It's interesting. I used to live in Canada, so whenever I visit I always revert to Commonwealth spelling.

0. I'm dreadful at spelling, but I usually do know when it's 's' and when it's 'z' :-)
1. I'm British, living in England at the moment
2. Yea, when I lived in the USA, I used the local spelling. When people spell well, using the 'wrong' spelling drives them nuts, so it helps to match the local convention.
3. I've never seen it called 'Commonwealth spelling' spelling before. Thank you for the information!
I lived in Massachusetts for a while, so it may still have been confusing :-)

Posted 5 years ago #
Silntknight
Moderator

I'm not sure I have that option. I'm not sure how it prints better. I would think that hatching causes a hatched pattern for a ground plane instead of an actual plane. I guess I can test that a couple of times. I'll use GIMP or Paint to manipulate it a bit.

I know a chemical regulatory affairs manager, so I'll talk to him about the regulations on the chemicals.

I would guess that it is always an "s" for Commonwealth (British) spelling, and a z in American spelling. I've heard the term "Commonwealth Spelling" before, but I guess it's not that common. I call it that because I know that many other places spell similarly, for example, every place Britain ruled except the US.

Posted 5 years ago #
gbulmer
Moderator

I'm not sure I have that option.

If your PCB design package doesn't do hatched copper pours, don't worry about it :-)
It's likely a lot of effort any other way, and a connection might get damaged.

BTW - DesignSparck PCB design package is free, much less limited than Eagle's free version, but windows only
http://www.designspark.com/pcb

I've never used it (Windows only, yeuk) but in the demo I saw, it looked very usable.

Posted 5 years ago #
Silntknight
Moderator

As I'm exploring that option (or maybe in a few hours), what do you think about the screen shots I posted? I am going to make a few minor adjustments, thanks to some new found space. Some resistors and the like are pretty packed, so I'll move them to give them some more room. Other than that, I think it is finished. Other opinions?

Posted 5 years ago #
gbulmer
Moderator

I find it really hard to comment without a schematic.

The separation looks much better.
I can't figure out which holes are for test points, and which maybe for off-board wires.

If a MCU signal is routed off-board, ensure there is a low value resitor (e.g. 270R) in series to protect against screw ups.

Posted 5 years ago #
Silntknight
Moderator

Ok, I'll try to make a schematic for this.

I haven't put any test holes in yet. Anything that has a yellow "box" around/near it is a hole for a component. The largest holes with no yellow are for screw terminals.
By the way, what's wrong with just touching the board on various traces for test points?

Why is this? I have 2 digital inputs from switches, 3 analog inputs, and 4 PWM outputs. Do I need to have a 270R on all of them? The PWM outputs actually go through an optoisolator, so the MCU signal doesn't even go off board.

Posted 5 years ago #

RSS feed for this topic

« Previous 12

Reply

You must log in to post.