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Forum Index : Microcontroller and PC projects : Full VT100 - 32mm square...
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Hi folks. 
Playing around with multi-layer board designs now, and this one is four-layer. This board is only 32mm square, but contains the full VT100, including on-board VGA socket, PS/2 socket for the keyboard, USB connector, 3v3 regulator, activity LED, colour select pads, composite video out, regulated 3v3 out, RXD input protection resistors and three pads to allow you to program the firmware into the chip in the first place. These are just solder pads, cos once you have the firmware in there, any updates can be via USB, so you should only ever need to do this once in an ideal world. Power for this module is via the USB cable. There is no provision for external power, but with the plethora of cheap USB charger plug-packs that can be had(often fitted with a USB A type socket), one of these and a USB cable and you have your "External" power. TOP (visual layer only): 
BOTTOM (visual layer only): 
INNER LAYERS: 
ALL LAYERS: 
Pin header at lower-right side of board allows for various connections and is 3v3, RXD, TXD, VIDEO OUT, GND - top to bottom. Smoke makes things work. When the smoke gets out, it stops! |
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kiiid Guru  Joined: 11/05/2013 Location: United KingdomPosts: 671 |
Slowly creeping towards my style 
Will meet you there. http://rittle.org -------------- |
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Zonker Guru Joined: 18/08/2012 Location: United StatesPosts: 761 |
Wow..! Awesome compact layout... Will keep an eye on this one... Good work Grogs..!  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Thanks guys.
I did not really NEED a VT100 this small, it was just an excuse for me to play with multi-layer. And Shenzhen's PCB prices are just too good for me to not have a play with multi-layer - US$22.90 for ten of these four-layer boards. Having set the PCB size, the mission was "Can I squeeze it all in there?" You would have no hope of doing this module, this small, without going multilayer, I would think.(prove me wrong though!) The PCB size came about based on the VGA socket footprint. It was 31mm wide, so add 1mm and make it square - that was how I came up with the 32mm square size. Smoke makes things work. When the smoke gets out, it stops! |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Grogster, that is very very cool. I hope you make some of these. I would love to see it. Nice work!!!! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Yes, I will be getting a batch of ten. I could panelize this design, but the price difference between 5x5 and 10x10 for four-layer is more then double. That's to be expected - they ARE four-layer boards...... But I will get at least a batch of ten - I'd never use that many. Not only does it give me a chance to play with multi-layer, but it also will give me some SSOP soldering practise - I have never soldered this tiny pin-spacing before - I was always too scared of it.
However, with a proper soldermasked PCB, the solder SHOULD want to flow to the pins, and not bridge them, due to the surface tension etc, and it's about time I faced my SSOP fear, as this would allow me to minimize my other designs, if I thought I could solder the things! 
I also need to finish my bleeping reflow oven - that's on the agenda for the Christmas holidays too. EDIT: Shenzhen can supply a solder paste stencil at the time of ordering, so I would get one of those. A couple of swipes with a blob of solder paste and a credit-card or similar, and your solder prep is done, then into the oven for baking. Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
UPDATE: Well, I have assembled one - the VGA and KB plugs show how small this board is. One thing I did find was that having the VGA on one side, and the USB on the other, the bodies of the plugs hit each other - I actually expected that. I will fix that problem by sanding down one side of a mini-USB patch lead for use with this board. These leads are a dime a dozen. 
Smoke makes things work. When the smoke gets out, it stops! |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3165 |
That is tiny, well done. Geoff Graham - http://geoffg.net |
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| viscomjim Guru Joined: 08/01/2014 Location: United StatesPosts: 925 |
Grogster, that is VERY cool. Nice job on 4 layer board!!!!! |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Have to say you're getting very good at this Grogs. Wait till we get to the next 'design-by-committee' four-layer job - should be a ripper.  |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
you could look at revisiting an old favourite - laying out a colour maximite onto a 4-layer board. credit-card sized with the board supported in its case by the VGA connector, using an external 5v regulator but on-board 3v3. cheers, rob :-) btw - saw one of your micromite single-layer boards in the flesh at the weekend, and was quite impressed with the results. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Thanks for the nice words, everyone. I doubt I will really use this size board much, so if anyone wants one of these, US$2.50 including airmail to anywhere on the planet. I have nine boards left out of the 10 I ordered. It was an exercise in 4-layer design more then actually NEEDING the PCB to be that small, but it was all good for practise. I remember a time - not that long ago - where I insisted all boards be single-sided design, with nothing smaller then SOIC and 1210 passives, and that was the smallest I was prepared to go to. SSOP was TOTALLY out of the question, as was any QFP pretty much. We are only talking three years or so ago here. It's amazing once you realize that you CAN hand-solder these tiny pin-pitch devices, that you start to experiment a bit more. Some select devices are only available in QFP or SSOP, so it opens you up as a designer, to many more possibilities if you can work with the fine-pitch stuff.  Smoke makes things work. When the smoke gets out, it stops! |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
Hi Grogs, This is a really useful skill to have - well done 
Out of interest, how many layers can go to when using the existing software that you are using? May just have to speak to you soon about some PCB work if you're interested
WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Four layer is the maximum that Sprint Layout 6 can do, but Shenshen2U can do six-layer boards if you want to submit them..... 95% of general-purpose designs can be had in double-sided, and of the 5% left over, 4% of that can be done in four-layer(probably!!!), leaving only extremely tight boards needing six layer or more. Computer motherboards being the exception here, as they will be multi-layer, me thinks - probably more then six layer most of the time, but I'm not designing them - yet.
Flick me a PM or email if you want to talk - I like doing PCB's.
...yes I know - I'm a sick little boy...  Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
UPDATE: It's a squeeze plug-wise, but all up and running with VT100 firmware 1.3 
You CAN'T get away with the bulky VGA plugs, but the thinner VGA patch cables that are all over the place have thinner(cheaper!) cable and thinner moulded plugs, so they fit fine. Smoke makes things work. When the smoke gets out, it stops! |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Looks good Grogs, Have you been having delays with Shenzhen? My last set of boards have been just shipped 12 days it took for manufacture (they quote 5-6), now the 3 week shipping time.. They also didnt send me a link to a picture of them, even though I ticked for that feature. Time isnt an issue on these ones but they seem to be slackening off a bit, unless there was another big holiday in China. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
I've had the same issue with lack of photos, and that was a nice touch. Does not REALLY bother me that much though - no photo. Time to make my latest 300 x 150 beast took about 12 days, but I always get DHL shipping, which normally only takes about three days from the time they email me that the boards have shipped. Perhaps they just have a lot of orders at the moment? Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
I've sold most of these boards already! 
There are three left. For those making the unit, here are some updated GIF images of the top and bottom for assembly purposes: TOP: 
BOTTOM: 
That should make life easier for those assembling the boards. All parts are standard 1206, regulator is MCP1703-33. USB socket is Element-14 part 2300434. The circuit is Geoff's VT100 except that I used a different regulator. The final version is green video only - I got rid of the colour-select pads. Green really is easiest on the eyes out of RGB! 3mm LED changed to 1206 SMD LED. 100n caps on regulator changed to 10uF - I just used the same X5R ones I use for Vcap, as I had them in stock, but X5R is a good choice for general use too, IMHO. Note that there are NO baud-rate pads or jumpers. Default baud-rate will be 1200. You use the internal config utility(SHIFT+F12) to set the options you want, so you will need to go in there and set the baud-rate. Initial programming of the firmware into the virgin PIC32 requires a LITTLE fuffing around. You tap into 3v3 and GND on the pin-header, and you need to tack-solder three thin wires to the bottom solder-pads labelled (C)lock, (D)ata and (R)eset. This gives you the five wire interface to the PICKIT3 programmer. So, to make things a little easier: "R" pad to PK3 pin1(MCLR) "C" pad to PK3 pin5(PGC) "D" pad to PK3 pin4(PGD) 3v3 and GND header pins to PK3 pin2 and pin3 respectively. Once you have the first firmware in there, any future updates are via the USB connection, so this only has to be done ONCE, to get the firmware + bootloader into a virgin chip in the first instance. Naturally, you remove these temporary wires once you have a running firmware in there. Solder-blob across the two small pads on the top side, just below the pin-header, to select bootloader mode for updates. You should not need to do updates very often(if at all) if you flash in version 1.3(+ bootloader!) when you start. Smoke makes things work. When the smoke gets out, it stops! |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1328 |
Grogs, here's a thought for future boards and to see what others think. I've got a good stock of 0805 resistors but very few 1206's (resistors that is), and I think for many people that's pretty common. I like the idea of using the 1206 pads because they're certainly easier to manually handle but as a compromise to handle both how about extending the 1206 pad design you're using inwards a little bit so that 0805's can be used as well. When I put together my Skinnymite board I used 0805 resistors on the 1206 pads and they came up well, but the connection relied on the solder's surface tension from the pad to the outside ends of the 0805's because there's no overlap. Having them overlap just a bit would help. The same's maybe true (though a lot less so) for 0805's in the smaller caps, especially the always needed 0.1 uF's. Getting the right value cap in a particular size and at a reasonable price or quantity break, is sometimes an issue. If either size could be used it would make sourcing some of them a bit easier. I'm definitely not suggesting you should go to 0805's generally unless you need to if you're trying to minimise board space. Greg |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9075 |
Good idea Greg, will take it under advisement. Smoke makes things work. When the smoke gets out, it stops! |
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