DIY tablet computer, maybe.

[awemawson]

I think it's generally seen as... uncouth or something to talk about price and money. But if someone says somethings cheap or expensive it's really a relative thing and it's hard to tell how they personally value things. For me £193 is definitely in the 'yowza!' territory.

Actual prices are probably important so people can see how much it's worth the idea of making your own mains power only tablet computer with a high chance of failure against just buying one. Plus calling it a tablet seems like a stretch if it's mains only. It's closer to an all-in-one PC really.

Simon, price or cost is often highly relevant in these matters. If you're giving someone a present and discuss it's price, or bragging about your costly new car, then yes that's uncouth, but letting people know what is a realistic price in an engineering discussion I believe is absolutely fine

[S. Heslop]

Boy howdy it's hot. I've been taking it easy and daydreaming about portables some more. I think the ideal device is probably the slider style phones they were coming out with before the stupid iphone ruined it and every manufacturer turned towards big solid cheap to manufacture touchscreen slabs.

Here's a doodle of a really bad idea for a chunky handheld games console.



Not a great idea at all really. I'll need to re-think it a bit. But something i've been hung up on for years is how... nice DSLR cameras feel. I think something with a similar form factor that's better than what I came up with might make a neat novelty device, if a goofy one. I believe those dirt cheap Rapberry Pi's are capable of playing the only game that matters - Doom (1993). Or more specifically the custom levels for Doom and its sourceports that people have been making for the last 25 years, refining their art. So it could be relatively cheap to slap together something silly some day.

[S. Heslop]

This is going a bit slow since i'm still waiting on stuff to be delivered. The cable came today though.


Got a few things soldered onto this tiny Tiny board, including the 3V voltage regulator. It's the first time i've actually soldered anything surface mount and it wen't just fine. Probably helps that it's still on the large side of surface mount!


I really hope I got the right wires in the right holes. The guy i'm following was lucky enough to have them colour coded. I went over them a few times and labelled them. I could perhaps test it on my desktop PC but it took so much to get the weird Chinese drivers that came with my current graphics tablet working that I'm not keen on risking anything that might break them. They still stop working when I open certain programs.



Here's the setup I used to record the soldering. All those weird extra adjustments on the legs finally came in useful. Check out all that "useful looking junk" in the shelves.

[vtsteam]

Now that's my kind of clutter! 

[S. Heslop]

Now that's my kind of clutter! 

I swear I just cleared the desk a week ago. I can't figure out where it comes from but its the same stuff every time.

[S. Heslop]

Holy mackrel. New problems. So the new power supply seems to make the PC run. A connected CPU fan spins and a keyboard can toggle the caps lock etc LEDs. But no video over HDMI. It's the only video output aside from LVDS.

So I figure maybe I can get a beep code out of it to try narrow the problem down. So I pull the case speaker out of a very old computer that's been sitting in a corner for years but I can't find the header on this motherboard. It's got headers galore to meet the all-in-one thin mini ITX standard but no PC speaker header. It does however have some LDC debug card header, so I look that up and find nothing. But there's similar looking connectors (9 pin header) called LPC and lots of shoddy looking circuits from China.

Man I was really hoping something would just work. I'm hesitant to go out and buy even more stuff to maybe get this working, but i'm half tempted by that debug card just to see if it's the CPU and memory causing the issues. They seem a likely candidate since they were sent in a god damn paper bag.

I think I might have a plan B if I can't get this PC to work. And i'll definitely return those components on the grounds of shoddy packaging.

[S. Heslop]

Here's the messy setup. Bar of aluminium as a temporary heatsink.



But just as I posted that last post a package arrived.



Kayzed1 sent me this cool laptop. Part of plan B was to gut it for parts but it's far too nice and useful. But it will give me a second computer to test the display and digitizer on without risking driver conflicts. It's got an older CPU but i'll also see how well it handles Krita.

[S. Heslop]

That panel at least seems to work. Or rather it switches on, makes a weird buzz, then switches back off and repeats. I suspect it's becuse I was using a tiny .75 amp power adapter but it's all i've got on hand at 12 volts. Boot sales are the best option for finding power adapters so hopefully the weather holds till Sunday.

Cant find my USB cale that matches the Tiny board either. I'm glad they finally came up with a USB adapter that can fit in both ways - but it's a shame they left a wake of hundreds of variations of the smaller sized ones.

I think i'm done for now. Just running up and downstairs to fetch stuff in this heat is killing me. I think i'll start concentrating on the case next. Might go with plastic rather than aluminium. Prices are about the same and aluminium would probably be the better choice - but I have access to a laser cutter. At least I think I do. If I can get the front assembled then i'd feel more comfortable flinging this very delicate display about to test stuff.

[ddmckee54]

Not sure that I didn't miss something, but is this "maybe tablet" just for funnsies - or are you planning on using it for a dedicated purpose?

Just askin'.
Don

[S. Heslop]

Not sure that I didn't miss something, but is this "maybe tablet" just for funnsies - or are you planning on using it for a dedicated purpose?

Just askin'.
Don

A bit of both. I've been wanting to do something like this for a while for various reasons. One is just to see if its possible. Earlier this year I was collecting some stuff to give it a shot, but ended up shelving it when I realised how expensive older generation CPUs still are. But right now i've found myself needing to ink a whole bunch of drawings as quickly as possible, and if all goes to plan i'll have even more in the future.

One of those Chinese pen tablet displays would probably be the most sensible option but I already had most of this stuff collected. Or at least I thought I did.


If I was going to take the DIY portable idea a bit more serious i'd be looking closer at stuff like those single board computers. Intel NUCs and all the weird stuff coming out like the UDOOx86. I might still in the future - especially as those boards are rapidly getting more powerful. I think whatever I come up with in this thread will be functional at best.

[krv3000]

lol I shod put a pic on showing my work bench

[S. Heslop]

Finally got something real done.


Not a straight edge in sight.

I'm going with steel and i've simplified the design a whole bunch since I want to actually get this finished. The steel is what I have on hand. I'm trying to stick to things I have now, like a keypad from an old mains powered calculator.



The idea is that the glass will be stuck to the steel - i'm gonna try that tape out. Then there's a plate behind the screen that screws into the front plate and holds the monitor in with some foam pads to act as springs so it's held flush against the glass but not with too much force. Then anything else will mount onto that rear plate.

The reason for the delay is that i've been caught trying to figure out how the font plate should look. Since once the glass is fixed to it I won't be able to drill any more holes in it I need to get that fully figured out.

Still thinking about how to join the sides of the box. I was thinking a few tack welds and hoping theres no serious distortions, but I figure i'd want the plate to still flex a bit to match the glass.


Oh yeah - does anyone know of any glass paint that sticks to glass really well? I want to mask the back of the glass off, the side that gets stuck down, with paint to hide the steel and tape behind it. Just searching for glass paint brings up arts and crafts type stuff.

[ddmckee54]

So the glass plate will be on the outside of the tablet in front of the steel plate with the important hardware screwed on the back side of the plate with screws through it?  You want to effectively black out the screws and the steel plate by painting over those areas on the glass?

If the paint's going to be on the back side of the glass you don't really need to worry about the paint getting worn or scratched so just about any rattle can of paint should work - as long as the glass is clean and dust-free.  I think when they black out around the edges of automotive glass they etch the area they're going to paint to ensure a good bond for the paint.  However I don't think this tablet will need to survive the exposure to the elements that automotive glass needs to survive.

Don

[S. Heslop]

So the glass plate will be on the outside of the tablet in front of the steel plate with the important hardware screwed on the back side of the plate with screws through it?  You want to effectively black out the screws and the steel plate by painting over those areas on the glass?

If the paint's going to be on the back side of the glass you don't really need to worry about the paint getting worn or scratched so just about any rattle can of paint should work - as long as the glass is clean and dust-free.  I think when they black out around the edges of automotive glass they etch the area they're going to paint to ensure a good bond for the paint.  However I don't think this tablet will need to survive the exposure to the elements that automotive glass needs to survive.

Don

The problem i've got is that the glass is also going to be a structural part to some degree, since it'll stop the display falling out forwards. And whatever paint I use will be between whatever adhesive I use to stick it to the steel. I guess it's still not going to be taking a whole load of pressure from the display so I could do some tests with the rattle cans i've got. I'm just assuming any old paint would practically fall off the glass.

[awemawson]

But the solvent in the adhesive may well react with the paint and either wrinkle it or not bond at all. You need to experiment with samples.

[PekkaNF]

Think that painting the glass is risky...I remember one design that needed something like that and design was between etching the glass or masking it, sandblasting and painting with epoxy.

Is it possible to paint metal rim and all that hardware behind the glass black? Tape is pretty transparent and probably attaches better to painted metal than painted glass.

The Tesa tape I use seems to be compatible with most of the paints, but reacted with one 2k alkyd paint (blistering).

[S. Heslop]

I'm glad I asked because I didn't even consider the tape reacting with the paint.

The hole in the plate was fairly crudely cut out, and I mesured the display wrong so there's a gap around the top and bottom too. I mean it's entirely concerns about how it looks so I could settle for this thing looking crude. I'm fairly sure it's going to anyways.

I took a closer look at those arts and crafts paints and it turns out they're a type you bake on in an oven, and are advertised as dish washer safe. So that's probably plenty strong. But worth testing with the tape.

[ddmckee54]

Depending on how "nasty" the solvents are that you are going to use with this, then your best option would probably be to sandblast the areas that are going to be painted to provide some tooth for the paint.  Then using an epoxy paint should provide the best resistance to solvents.

Personally, I think I'd just try cleaning the glass REALLY well, painting it with a good quality brand rattle can paint and assemble it, maybe baking the glass at a very low temperature for a while to be sure all the solvents are driven off before assembly.  Worst case you've got to peel the tape off the steel plate before you try it again and maybe get some more glass.

Don

[nrml]

Instead of etching and painting the glass, why don't you get a vinyl sticker in the colour of your choice cut out on a plotter-cutter and stuck down. It would be cheaper, easier and probably tidier. It wouldn't need more than a good clean and degrease before sticking down. It wouldn't take you long to get a template drawn and emailed off to a sign-writer or similar on ebay. Vinyl stickers are used on plastics very widely. The probability of chemical damage occurring is far less than with paint.

Here is the 3M VHB tape design guide. They have a lot of very useful data sheets and videos if you do a quick search. http://multimedia.3m.com/mws/media/441448O/vhb-tapes-design-guide.pdf
Sorry for going on about it. I can't help feeling that it would be just the ticket for your project. Page 14 might be interesting to you.

[PK]

Think that painting the glass is risky...I remember one design that needed something like that and design was between etching the glass or masking it, sandblasting and painting with epoxy.

Agree

We did a bunch of testing and what worked well for us was:
Sandblast
Paint immediately.
Paint
Paint
Paint
Cure for a long long time
Glue with a non rigid, non shrinking, neutral cure silicone. (I suspect tape with a little bit of thickness and flexibility would work better).

We've just (ie this batch) given the painting away and now bond a thin, opaque, layer onto the back to create the mask effect. It gets put in the squish-o-matic to force air bubbles out..

PK

[S. Heslop]

Instead of etching and painting the glass, why don't you get a vinyl sticker in the colour of your choice cut out on a plotter-cutter and stuck down. It would be cheaper, easier and probably tidier. It wouldn't need more than a good clean and degrease before sticking down. It wouldn't take you long to get a template drawn and emailed off to a sign-writer or similar on ebay. Vinyl stickers are used on plastics very widely. The probability of chemical damage occurring is far less than with paint.

Here is the 3M VHB tape design guide. They have a lot of very useful data sheets and videos if you do a quick search. http://multimedia.3m.com/mws/media/441448O/vhb-tapes-design-guide.pdf
Sorry for going on about it. I can't help feeling that it would be just the ticket for your project. Page 14 might be interesting to you.

Sign vinyl is a good idea. I was thinking about some sort of thin plastic sheet last night and I don't know why I didn't think of self adhesive vinyl. I can get that from a regular hobby store and it'll probably cut fine with a ruler and scalpel.

I'm interested to hear about this tape though. And adhesives in general. I like the general idea of adhesives but outside of wood glues and loctite i've had nothing but disappointment. But i've got high hopes for this tape doing what I wished hot glues could.

[S. Heslop]

Not a whole lot of progress. Still waiting on that glass. The guy that cuts mirrors, which are in the same order, is off work for personal reasons. I'm not in a huge hurry though since i've got a few other things i'm trying to get done.


The back plate is just solid right now, but once I figure out where things aught to go i'll start cutting bits out of it to lighten it.


The first attempt at these stand-offs were a complicated part with a thread cut in one end and a screw hole in the other. I made one before realising it'd be alot easier to just part the bar off, tap a hole through it, and use a bit of threaded rod on the bottom. Need to get some countersunk screws too.

[S. Heslop]

Sides cut and welded on.


You can see how the stepped sides work. A sleek and modern device for 2018.


The top still seems to be somewhat flat as far as I can tell. It's as flat as that plywood bench at least. I found a cheap Clarke mig welder earlier this year with a broken trigger and i've not had an excuse to roll it out much till now. I'm getting a sooty weld which as far as I know means the gas flow is too high.

[awemawson]

Simon,

Have you an idea what this is going to weigh? You may need muscles like Super Man 

[S. Heslop]

Simon,

Have you an idea what this is going to weigh? You may need muscles like Super Man 

It's already pretty hefty and it's just the shell!