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Homemade Tablet
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 27 Nov 2011 12:52:37 pm    Post subject: Homemade Tablet
Well, with the release of Raspberry Pi sometime in December, I thought I'd look into building a tablet. Predicted parts:

Raspberry Pi A or B
Touchscreen
Battery (This will have a 300mA draw (700mA for the B version), and will need to provide that through a Micro USB cable)
Wireless Ethernet USB Dongle
SD card (Persistent storage)
USB Hub
A case of some sort.

I know where to get most of this stuff, but I don't know where to get a touchscreen, or a battery that meets those specs. I've been pointed to various places by tifreak and Kerm, (To eBay and someplace else) but they had doubts that I would be able to find a screen big enough. If anyone has Ideas on where I could get such parts, it would be appreciated.

EDIT:

Raspberry Pi FAQ wrote:
Can I run power Raspberry Pi from batteries as well as from a wall socket?
Yes. The device should run well off 4xAA cells.


What it doesn't say is how to do this. I'm not really sure what they're talking about.
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comicIDIOT


Guru


Joined: 01 May 2006
Posts: 5105
Location: SFBA, California
Posted: 27 Nov 2011 01:25:28 pm    Post subject:
As for the batteries, it would be setup like any other battery device. The batteries create a circuit with the device. It's nothing different from device to device.

My knowledge ends there, so I'll let others correct, agree or add-on to what I have said.
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 27 Nov 2011 01:27:08 pm    Post subject:
comicIDIOT wrote:
As for the batteries, it would be setup like any other battery device. The batteries create a circuit with the device. It's nothing different from device to device.

My knowledge ends there, so I'll let others correct, agree or add-on to what I have said.


Well yes, I know that... I mean in terms of how to hook them up, and that sort.
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D(+) G e-(*)>++@ h! r!>+++ y?
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willrandship


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Joined: 06 Jul 2010
Posts: 558
Location: Between Venus and Mars
Posted: 27 Nov 2011 04:42:49 pm    Post subject:
Well, if you're going NiMH the charging hardware is more modest, but with a Li-Ion battery you'll want an overcharging protection circuit.
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 27 Nov 2011 04:43:45 pm    Post subject:
willrandship wrote:
Well, if you're going NiMH the charging hardware is more modest, but with a Li-Ion battery you'll want an overcharging protection circuit.


/me is still very confuddled.
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willrandship


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Joined: 06 Jul 2010
Posts: 558
Location: Between Venus and Mars
Posted: 27 Nov 2011 10:56:43 pm    Post subject:
NiMH means the type of rechargeable you buy in the AA form factor, that was made after, say, '99 (older ones are NiCd, which suck in many ways) whereas Li-Ions are the ones you have in Cell phones, laptops, and other stuff.

Li-Ions hold about twice as much, but have a tendency to explode if overcharged. Hence, NiMH is safer. Plus, it uses greener materials, if that matters (not saying production is greener, but waste is)

Also, you can buy NiMH far more easily.
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 28 Nov 2011 05:01:23 pm    Post subject:
willrandship wrote:
NiMH means the type of rechargeable you buy in the AA form factor, that was made after, say, '99 (older ones are NiCd, which suck in many ways) whereas Li-Ions are the ones you have in Cell phones, laptops, and other stuff.

Li-Ions hold about twice as much, but have a tendency to explode if overcharged. Hence, NiMH is safer. Plus, it uses greener materials, if that matters (not saying production is greener, but waste is)

Also, you can buy NiMH far more easily.


I know about all that. What I'm asking here is, how would I hook this stuff up? I'm not very clear on that bit. More on the anti-vaporware bit: The Register's take on this. Here's a circuit diagram to clear a bit of what I'm trying to do up:

link
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 05 Dec 2011 04:48:41 am    Post subject:
***BUMP***

So... There's beta pcbs now. And they really are credit card size. Anyway... Tablets. I would really like to get a post from some of our hardware hackers (*Cough* Kerm *Cough*) who have skipped this topic...
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55733
Location: Earth, Sol, Milky Way
Posted: 05 Dec 2011 11:53:58 am    Post subject:
If you can find a nice, cheap, touchscreen, I would be very happy. I've been trying to source one myself and have thus far been unsuccessful.
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alberthrocks


Power User


Joined: 29 Jul 2010
Posts: 403
Posted: 05 Dec 2011 12:09:44 pm    Post subject:
I think you can simply buy the 4 battery case, and then hook the + and - ends to a USB male port, depending on the pins of the USB micro USB. These can be found on Mouser, and potentially many other electronic hobbyist retailers.

Kerm: Depends on how big the touchscreen. Wink If you are truly aiming for tablet, it's going to be hard, even with the resistive ones... for this guy [Raspberry Pi], I'm going to be aiming for an iPod Touch form factor, since it's guaranteed to be pretty darn cheap.
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KermMartian


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Posted: 05 Dec 2011 12:44:37 pm    Post subject:
Albert: absolutely not. You need a voltage regulator on it, either of the 5V low-drop variety, or (maaaaaybe) the 5.1V zener diode trick. For supplying power to a whole board, I would probably go the discrete regulator route. Regarding touchscreens, something 3" diagonal or so is what I want, ideally in the $20 or less range.
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 05 Dec 2011 04:42:54 pm    Post subject:
KermMartian wrote:
Regarding touchscreens, something 3" diagonal or so is what I want, ideally in the $20 or less range.


I remember you mentioning places to buy touchscreens on irc, but I can't remember where. Could you post them here?
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D(+) G e-(*)>++@ h! r!>+++ y?
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alberthrocks


Power User


Joined: 29 Jul 2010
Posts: 403
Posted: 05 Dec 2011 10:39:28 pm    Post subject:
KermMartian wrote:
Albert: absolutely not. You need a voltage regulator on it, either of the 5V low-drop variety, or (maaaaaybe) the 5.1V zener diode trick. For supplying power to a whole board, I would probably go the discrete regulator route. Regarding touchscreens, something 3" diagonal or so is what I want, ideally in the $20 or less range.

Ahh yes, forgot that even AA batteries can fry a device in a few seconds. :/
My bad.
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Nick


Newbie


Joined: 30 Nov 2011
Posts: 25
Location: Belgium
Posted: 06 Dec 2011 12:07:29 pm    Post subject:
http://www.directron.com/id800t.html

there you can find a touch screen image viewer, maybe you can disassamble it, sincs it's ony $70 for a 800*600 touch lcd, the quality will be in the same range as the price i think, but it might help to see if everything works
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55733
Location: Earth, Sol, Milky Way
Posted: 06 Dec 2011 12:58:53 pm    Post subject:
Nick wrote:
http://www.directron.com/id800t.html

there you can find a touch screen image viewer, maybe you can disassamble it, sincs it's ony $70 for a 800*600 touch lcd, the quality will be in the same range as the price i think, but it might help to see if everything works
The difficulty there would be seeing how much extra interface circuitry you'd need to make that work with the Pi. Ideally, we'd be able to find a nice LCD that requires minimal interface circuitry. I believe we need something with the LVDS interface?
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willrandship


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Joined: 06 Jul 2010
Posts: 558
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Posted: 10 Dec 2011 07:19:46 pm    Post subject:
Actually, DVI. Or Composite. That is, on the Pi's end. You're not likely to find DVI in embedded electronics, but composite is fairly common. LVDS is even more common Razz

Then the touchscreen has some sort of interface of its own.
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seana11


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Joined: 23 May 2011
Posts: 833
Location: Well, the sign says "You are here"...
Posted: 11 Dec 2011 08:28:09 am    Post subject:
willrandship wrote:
Actually, DVI. Or Composite. That is, on the Pi's end. You're not likely to find DVI in embedded electronics, but composite is fairly common. LVDS is even more common :P

Then the touchscreen has some sort of interface of its own.


Hmm, maybe I could figure out some way to make it look like a touchpad, from the pi's end. Some of the DEs have options that can make a touchpad behave like a touchscreen.
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GCS d- s+: a---@ C+++ UL++ P L+++ E- W++ N o? K? w--- O? M--
V- PS++(--) PE- Y+ PGP t 5? X(+) R tv-- b++(+++) DI+(++)
D(+) G e-(*)>++@ h! r!>+++ y?
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willrandship


Expert


Joined: 06 Jul 2010
Posts: 558
Location: Between Venus and Mars
Posted: 11 Dec 2011 09:07:16 pm    Post subject:
figure out some way to make it USB and you don't need to do anything, but anything else will require more work on the Pi's end.

Edit: Wow, check out this thing. Sure, it's only 320x240, but it's also only $20!

http://www.dealextreme.com/p/3-5-tft-lcd-monitor-visual-reversing-vehicles-reverse-camera-ntsc-pal-dc8-15v-49796
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Jim Bauwens


New Member


Joined: 05 Dec 2006
Posts: 96
Location: Belgium
Posted: 12 Dec 2011 08:59:44 am    Post subject:
There are some USB (display link) screens that have touchscreen.
I have an 800*600 7 inch screen (without touchscreen) of samsung, and it only costs 50 euro.
Linux has displaylink drivers, so you should be able to use them without a hassle Smile
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55733
Location: Earth, Sol, Milky Way
Posted: 12 Dec 2011 12:00:15 pm    Post subject:
jimbauwens wrote:
There are some USB (display link) screens that have touchscreen.
I have an 800*600 7 inch screen (without touchscreen) of samsung, and it only costs 50 euro.
Linux has displaylink drivers, so you should be able to use them without a hassle Smile
Hmm, that's not a bad price at all for something like that! Ideally, I'd like to be able to find something around 4" or so, with a resolution near 640x480 pixels, resistive touch would be nice, around the $20-$30 mark.
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