Feedback for an LED matrix board

[m00dawg]

Howdy Folks!

I was hoping to get some feedback on some changes I made to my LED Matrix board. To save on space, I opted to mount the diodes for the buttons under the button itself. I was thinking I could solder the diodes on the back side to avoid solder blobs that might prevent the button from mounting flush. I was curious as to people's thoughts on if this is a good idea? It saves a ton of space and, otherwise, I would have to shift everything over on my control surface which I wanted to avoid since I'm otherwise happy with my layout.

This is not a board I care to etch on my own so I was going to order it from BatchPCB though if enough people were interested (25 seems to be the magic number), I was going to see about organizing a bulk order.

[m00dawg]

Doh! I realized I can save 2 pins by using JD8-D1 and JD8-D2 from the LED headers. Wilba, if you happen to see this, can you confirm this is correct? The button wiring diagram for the MB-6582 didn't include the matrix buttons, so I went off the MB-6582 control surface board layout itself.

[rosch]

very nice! i'm interested, i could use at least 2 or 3

[m00dawg]

Well, that puts us up to 5 :)

Also, here is the revision sharing the LED pins. I'm pretty sure that's right but not sure enough to order any boards just yet :) I opted to share those pins since I am going to use the MB-6582 baseboard for my synth. Wilba's transistor sink magic, though I don't quite understand it, could be applicable elsewhere too. If enough people are interested, I guess we'll need to see what everyone would prefer there.

EDIT: 4pcb came back. 25 boards @ 3-day turn-around ends up being $15.08 each (not including shipping). I need to talk to someone there but there is also an option for longer leader times. 4-week lead time, for instance brings the cost for 25 down to $9.37. Don't yet know about shipping since that will drive the costs up for everyone just a bit (since it has to get shipped to me then out to everyone). I'm in the US so I'm not sure how international rates apply there (haven't done that before :) )

Edited March 22, 2011 by m00dawg

[ilmenator]

If it was my board, I would go smd for the diodes. That way, soldering the diodes on the "back" side would be natural, and the whole thing would still look nice and tidy. 4148s can be had in MiniMelf (MMA) 0204 L=3,6mm, Ø=1,4mm, which is not too bad to solder even for beginners.

[m00dawg]

I was thinking about that last night too. Are you referring to something like this? I would have to see it a bit closer to know how much of a pain that could be but it's probably easier than soldering the GM5 (which was actually not bad, just slow) and, yeah, I agree, that would totally solve the problem of the diodes messing up the buttons.

Actually, I was thinking about use SMD buttons for another board (the one surrounding the LCD panel) but was worried about alignment being a problem if one wasn't spot-on with the surface soldering. That and I can't find SMB 6x6 buttons with a 13 or 15mm button-length.

[ilmenator]

I was more referring to something like this. But any package/case you can get across should be fine as long as you feel comfortable with its size. MiniMelf is quite standard, i.e. available all over the world (my part of the world? :rolleyes: ).

[m00dawg]

Ah ok. I was actually thinking about the flat-mount SMD devices (so basically like the one I linked to but with only two pads). Is there a particular technique to MELF's? I see glue is recommended to keep them in place until you solder them. What about the soldering technique anything concerning there?

I guess I'll see what's available in EagleCAD and go from there :) Really, if it's just SMD pads, I wonder if I can make a design that would work for flat or MELF-mounts (seems like that is plausible).

[ilmenator]

What about the soldering technique anything concerning there?

Put some solder on the tip of your iron, take some pliers and grab the component on one end and place the other end on top of one of the pads. Solder the one end with the solder that is still attached to your iron's tip. Then do the same with the other end of the component. Use solder flux for best results. It's really as simple as that.

The glass body of the diode is actually really handy as it does not stick to the pliers. If you let the one end of the diode cool down before you solder the other, then the component should not move away from its place - again, flux helps.

[rosch]

from your schematic it seems like there's plenty of room even if using through hole components. if you're doing double layer boards anyway and they're on the back they'd just have to be soldered at first.

another question: is there enough room between the screw holes and the switch for the head of the screw to fit?

[Flying Panther]

I'm interested as well! I'm not even near designing the control surface, but a nice PCB for the matrix will make things a lot easier when I get to it :)

[m00dawg]

@ilmenator

That's about what I was thinking. I wasn't sure about the way the solder would flow off the barrel since I'm used to components with a direct contact to the pad. Doesn't seem terribly difficult and I like not having through holes there.

@rosch

The through-holes could become a problem as they are quite close to the border of the button. Soldering the diode on the underside helps, but it still has leads that would poke out and need to be trimmed. I agree with ilmenator that SMD is a good way to go and may be a nice practice board before going to the GM5 or OPL3. Not really much to mess up for something like a diode. But, as far as a bulk order goes, as long as functionally the non-SMD board works, then I guess it's more up to those interested.

@Flying Panther

Ask and ye shall receive :)

[rosch]

ok, now i got it, i didn't think of the contact to the switch.

i just put myself down for 3 in the wiki.

i'm not in a hurry, so i can wait for the lower price

i guess i still can increase that in case we take the 4 week lead time?

cool!

[m00dawg]

Yeah you can put whatever quantity you'd like :) It's just a tally until we meet the minimum number of orders, at which time I'll start checking with people to see who still wants them and then if the final count is still above the minimum, we can start going. The 4 week lead time is akin to BatchPCB. I would expect 6-8 weeks all told for people to get their boards at least to international places. I'll iron that out if/once we hit the minimum amount of boards.

I didn't put it down yet, but we can have choice of fancy colors if people care about that sort of thing (there's a cost difference so keep that in mind). I know people liked red for the GM5x5x5 boards for instance.

Finally, here are some SMD options in case there needs to be discussion about which parts to use. This is what I found in EagleCAD just looking at random diodes, so it's not matched to any specific ones, though I would imagine there would be signaling diodes that we need in most all the packages.

In order:

* MICROMELF-R

* MICROMELF-W

* MINIMELF

* DO-214AC

* DO214AC

The last two I guess are variants of each other. There's more in Eagle but some didn't fit without running into the pads. It seems like the MINIMELF and DO214AC pads are close enough such that people could use either/or.

I haven't looked at specific parts on Mouser yet for these - just wanted to share some random findings :)

[Flying Panther]

I've put myself down for one as well. Looks like the third lowest (MINIMELF / DO-214AC / DO214AC) would be able to share the same soldering pads. Also those pads look big enough to confidently solder them without getting scared for SMD ;)

As for the color, I'd be happy with an 'average' green board with white silkscreen, as all other boards I orderd up untill now are that way.

[m00dawg]

Agreed! I went ahead and put in the DO214AC, though I put in the smaller of the two. The larger one had me a tiny bit worried about any bridges. I'll post an update here once I have some extra time (still at my day job :) ).

I, too, am ok with green. Purple sounded neat but, I mean, who is going to see them :) Unless someone is making a clear control panel of course.

[m00dawg]

Ok board layout updated to use SMD diodes, among other minor edits. Turned out pretty well and saved a tiny amount of space. I could not bring in the dimensions of the board much more without Eagle complaining. I may be able to push those limits depending on what 4pcb or BatchPCB's design limits actually are. I also noticed I can shave like .025" by using smaller wire, though I hope people are not quite that space constrained.

In any case, the changes can be found here. I also included a parts list with a link to some SMD diodes I found on Mouser that should work.

[rosch]

here's also a link to the diode at Farnell:

http://de.farnell.com/jsp/displayProduct.jsp?sku=1469425&CMP=KNC-GDE-FDE-GEN-SKU-G12&s_kwcid=TC|13114|1n4148w-v-gs08||S|e|5480397067

[Stormcaller]

In theory could someone take this board, wire the output to a second board with multiplexers on it to connect to J2 on a sammichSID and allow you to connect a modulation matrix to one as an external unit?

Edited March 24, 2011 by Stormcaller

[m00dawg]

You should be able to extend the sammichSID, yes. You can always just use the base board and make your own control surface by chaining your ins and outs. It looks there is also extra headers on the top board too, giving you some nice potential options.

Keep in mind that buttons for the current iteration of the above board are sharing 2 pins with the LEDs as I was going to use the MB-6582. Both the LEDs and buttons share JD8 so I was able to save some space. I am thinking of going back to the old way, however, so individuals had some options since one can always connect the buttons to the JD8 header using some other means.

Either way, the design assumes that a button and LED matrix are used (ala MB-6582) so I would check here for some info on that. Wilba described how it works in greater detail in a forum post but I haven't found it yet to give you a link (it's there though, I looked at it last week :) ).

EDIT: Doh I forgot to mention while I had the floor :) I am planning on offering both SMD pads *AND* through holes for the diodes. That the outline for the 6x6 tactile switches is elongated in Eagle such that using through holes, while close, should be fine in many cases. I think I'm still going to bust out some hard-core SMD action, those wanting their own board can now use either/or. Thanks to SmashTV for providing the info and most excellent suggestion!

The one caveat is that I need to use octagonal pads for the through hole diodes so they will take a bit more effort to solder (not much). I could use elongated pads but they would make the board slightly bigger and I would put some components closer than I would prefer. I'm still working out some of the details but will post an update here and on the wiki once I have that finished.

EDIT 2: (sorry I just drank a tall glass of Promised Land Dairy Chocolate Milk so I'm kinda wired :) also welcome to the forums, Stormcaller!

Edited March 25, 2011 by m00dawg

[m00dawg]

Finished adding through-hole option for the diodes. Either is now an option. The through-hole option should accommodate diodes in a D-7.5 package. I would still recommend the SMD option but it's nice to have choices :)

I am still debating on whether or use a separate pins for the tactile switches or share the two LED pins. I tried to have it both ways but I think that could make things a bit cramped so I'm going for an either/or here most likely. I'm leaning towards adding the dedicated pins back just so there were more options since one can combine the outputs using other means if the bottons and LEDs are sharing the same pins (on the MB-6582, they all share JDB).

Updates are on the MB-SIDR8TR wiki page.

[m00dawg]

So I've been distracted as of late while working on my band's album which centered more around the NES than the SID. I plan on picking up my MB-SID design here soon which includes the LCD Matrix. It will likely be the first board I'm going to order. Since it's been a while, I wasn't sure if folks were still interested in a bulk order? If so, I'll go ahead and start one on the proper forum but if not I'll likely add this to my BatchPCB list to have made when I'm ready to pull the trigger.

The board design I'm pretty happy with so unless folks want the discrete header for the buttons (the 2 pins shared via JD8 on the MB-6582 baseboard), I can't think of much that needs to be changed at this point.

This before, the design is untested so be sure to consider this if interested in the bulk order!

[rosch]

i'd be in for one, definitely, in case you make them :)

[m00dawg]

Ok I'll go ahead and push out the latest revision (mostly just has some silkscreening on it being the difference) and perhaps look at putting up a bulk order in a few days.

[m00dawg]

Had more time than I thought so I went ahead and uploaded the latest board design to the wiki and create a post for it. Not holding my breath that will hit the minimum order anytime soon but there it is anyway :) I'm still a ways out for likely needing to start ordering boards so there's time yet and if we get more folks interested, I could likely wait a little while longer.