
Add a dirt-cheap screen to the Raspberry Pi B+ - nmilford
http://blog.reasonablycorrect.com/raw-dpi-raspberry-pi/
======
freehunter
This really should be the next thing the RPi team tackles, IMO. It's nice we
have this great cheap computer, but trying to find a screen to plug into it is
terrible. A computer monitor or TV is fine, but both of them draw too much
power and are far too big and stationary. And have you seen the prices of
small HDMI screens? I can buy a 8" Windows tablet, full PC mind you, for the
price of a single 5" HDMI screen.

Far too often I find myself saying "it shouldn't be this hard". Surely there
exists a market for an adapter to plug an easily available iPhone screen into
an RPi?

~~~
derekp7
What I'd like to see is a calculator shell that you could pop the RPi into,
including physical buttons, lcd screen, battery and charger. My thinking --
most high schools require a graphing calculator, such as the TI 89 or similar,
which is around $100 or so. Imagine if for that $100 you get something that
can act as the same calculator, but morphs into a full computer when plugging
in a keyboard/monitor? It may end up getting a lot more kids into programming
that way.

~~~
Phlarp
And then you have to buy a graphing calculator anyway because no high school
teacher / university professor will let you take tests with it.

~~~
derekp7
Because of cheating? How can you use the Raspberry Pi (in a calculator shell)
to cheat, in such a way that you can't use a ti-89 to cheat? Most cheating
will be by either storing crib notes on the device (which won't do you any
good in math if you don't understand the concepts), or by running a program to
solve a problem for you, both of which the ti-89 is more than capable of doing
-- that is its whole purpose, is to run math programs.

The ideal situation would be where the RPi foundation uses its existing clout
to get a PiCalc accepted as a standard calculator in school.

~~~
Crito
Standardized test calculator rules in this country are not governed by reason.

For instance, a TI-89 is allowed on the SATs, but a TI-92 is not. Basically
the same calculator, except the TI-92 has a qwerty keyboard. How would a tiny
little qwerty keyboard actually give you an advantage on a test like the SAT?
Who the hell knows. Remember 10 or so years ago when teenagers were all typing
on telephone keypads?

On the other hand, the advantage of a TI-89 (with a CAS) over a TI-83+
(without one) is fairly extreme.

 _(Also, anyone who bothers to google it can trivially get around the reset
key combos for at least 83+
line:[http://brandonw.net/calculators/fake/](http://brandonw.net/calculators/fake/)
Somebody who takes the time to program their calculator for cheating on a test
can do this)_

~~~
mdturnerphys
The TI-92 with its keyboard was banned not because it would help the test
taker, but because of a worry that the full keyboard would enable copying the
test to send to someone in a later timezone.

~~~
Crito
I am skeptical that it would be of any help, particularly since the calculator
is only allowed to be out during the math sections, not during the
language/written sections.

With the 89's input history, you could effectively record the mathematics
section merely by running it all through your calculator and then extracting
the history after the fact.

------
Someone1234
This looks extremely fun, and I can see it being used for creating homemade
mobile devices, and stand-alone packaged hardware.

I will say fun and small size notwithstanding the current cost of doing this
($50) is a little high relative to just buying a super-low end LCD monitor
($85 for an 18" by Samsung, Asus, and Acer, $54 for a refurb from NewEgg). But
I'm sure that misses most of the point...

Just seems like the $30 for the 5" LCD is a little steep but maybe you're
paying a premium because it is so small(?).

~~~
robertely
[Author] The premium was mostly Adafruit markup and convenience. I'm totally
not mad at the price, I received parts next day. If I really wanted to save
money I would design an adapter board, and order bulk screens from China.

Keep in mind this is prototype cost, typically inflated seriously because it's
a one off.

~~~
paulgerhardt
How does this compare with some the Raspberry Pi screen kits from China?

I see you can get a generic Pi LCD for $7.65, a 5" LCD with video in for
$18.75, and a touchscreen Pi size kit for $19.90[1].

Going to the effort of breaking out DPI through the GPIO was quite creative.
If optimized do you think these can hit sub $5? Either way, this was very
clever. Thank you for taking the time to document this for others!

[1]
[http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB...](http://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20150305102546&SearchText=5%22+tft)

~~~
robertely
So, these are almost all crappy clones of this:
[http://www.adafruit.com/products/1601](http://www.adafruit.com/products/1601)
It's fine for static images and low quality video, but its using the SPI bus
and a custom driver. This severely limits size of the display and/or refresh
rate.

~~~
makomk
Yeah. This might change if the Chinese companies get wind of this technique;
if I recall correctly these kinds of parallel LCD panels aren't all that
expensive. (Edit: Actually, the controller chip used in those existing Pi LCD
modules seems to support the required interface, it's just not pinned out.
They could probably make new versions of the modules that are wired up
properly.)

~~~
rasz_pl
there is no controller needed, every single laptop LCD panel from ~10 years
old was parallel. Then we got LVDS. Laptop screens from ~7(?) years ago have
LVDS deserializer chip on the Tcon pcb (DS90C562/SN75LVDS86), you can desolder
that and connect directly to parallel bus. Never screens integrated
Flatlink(lvds) receiver inside main lcd driver chip.

LVDS is just serialized parallel video. Serializer chips are ~$5 in singles on
Mouser. Combining Pee DPI output with SN75LVDS84 ($2.5 if you order 10 from
china) will allow you to connect any modern <=1366x768 resolution (single lvds
channel limit) Laptop LCD screen. Those can be free if you have a broken
laptop. You could even drive older "HDReady" 32' TV LCD with pee this way.

------
gourneau
For about the same price ($60) you can get this fancy little HDMI display
[http://www.adafruit.com/products/2260](http://www.adafruit.com/products/2260)
For $20 more it comes with a touch screen. It is great for little BBB or RPi
projects, zero config required for the BBB.

~~~
mark-r
The price I get at the link shows $60 only if you're buying 100 at a time,
it's $75 for one. Still nice to know about though.

~~~
xrjn
You can get them for under $20 if you buy them from China
[http://www.aliexpress.com/store/product/Free-shipping-LCD-
mo...](http://www.aliexpress.com/store/product/Free-shipping-LCD-module-Pi-
TFT-2-8-inch-320-240-Touchscreen-Display-Module-TFT-
for/1362008_1969913024.html)

~~~
danellis
You're comparing 5" with 2.8", though.

------
makomk
Wow, didn't know that you could do this with the Pi. People have been doing
this with the Cubieboard since it came out[1], but to be honest I'd always
assumed the Raspberry Pi display outputs were as tightly locked down behind
the binary GPU blob as the CSI camera connector.

[1] See for instance [http://linux-sunxi.org/Cubieboard/LVDS](http://linux-
sunxi.org/Cubieboard/LVDS) \- I believe it supports DPI as well as LVDS.
script.fex is basically Allwinner's equivalent of the device tree.

~~~
rasz_pl
You were right, they ARE tightly locked behind ze blob. It took a Broadcom
Senior Principal IC Designer (Gert Van Loo) to enable this interface, and it
only happened because he made a VGA output board (vga666), he didnt even think
about LCDs (something interface was designed for at the time this chip was
landing in cellphones).

I get the feeling DSI will never happen, or it will be as crippled as CSI -
locked down with blob to working with one official product only.

------
MichaelTieso
This has been an issue for me for awhile. I've been scouting for screens for
awhile for something cheap. I've been visiting GoodWill often as they have a
large selection of monitors to choose from but most of them are far too large
for a small screen. $15 is a great deal for a cheap monitor, but it takes up a
huge amount of room.

------
agumonkey
How many old laptops are thrown away ? They have nice LCD, and for 50$ I'd be
tempted to snip a LCD controller on ebay. Less educational, more eco-friendly.

------
rootbear
The pi-s have a display interface connector for DSI panels, and they are
planning to bring one out, but it seems to be taking a long time. The intent
is that it will be very inexpensive, in line with their education focus. The
resolution I saw mentioned was 800 x 480, like the one in this article. A bit
small, but usable.

------
ChuckMcM
This is an awesome post. A number of older laptop screens use this "standard"
and you can just take off the screen and repurpose it. The trick is that
sometimes the flex cable between the screen and the laptop has extra stuff on
it.

Time to go panel hunting for some more panels :-)

~~~
rootbear
I was wondering recently what the interface is on my old Nokia N800 tablet,
for just this reason, but I'm reluctant to take it apart to find out. And I
still have a soft spot for my trusty old N800. I also have an XO-1 OPLC
laptop, but it has a funky display. Hmm. I have an old IBM T60 in my junk
pile, maybe that could be used...

~~~
ChuckMcM
Heh, if you want a matching XO-1 I've got a spare :-)

------
ceeK
A friend of mine is currently working on a Raspberry Pi laptop, with a DIY
kit. Quite similar. www.pi-top.com

------
vwruetag
I'm aware that this is not comparable to a 800x480 display but if you just
want to output some simple monochrome graphics the 1.6" Nokia 3310/5110
Displays are quite nice. Very easy to drive and really dirt cheap - they can
be found for about $3!

------
lbotos
as an aside, the game on the screen is Gunstar Heroes which is an incredible
side-scroller that everyone should play at least once:

[http://en.wikipedia.org/wiki/Gunstar_Heroes](http://en.wikipedia.org/wiki/Gunstar_Heroes)

------
ilaksh
I can get a whole Android tablet for $60 with higher resolution. Why cant I
buy just the screen for $25?

Basically take the tablet manufacturing process and remove most of the stuff
thats not a screen and add HDMI.

------
runewell
It's truly amazing how someone can now put together a brand new computer for
less than $100 with a bit of effort. I have the Raspberry Pi 2 and it's quite
impressive, especially when running on an ARMv7-compatible Linux build.

------
chisleu
Maybe they can tackle the long-lived, widely-experienced SD card corruption
issues of the RPi in the next version instead of adding a bunch more pins and
an extra core.

Meanwhile the competition even has eMMC in the same price range.

~~~
tdicola
This comes up with every Pi post on HN for some reason, but if you're getting
SD card corruption you either have a bad card (check the known good cards:
[http://elinux.org/RPi_SD_cards](http://elinux.org/RPi_SD_cards) ) or are not
shutting the Pi down correctly. You absolutely cannot just pull the power cord
out while booted up because the SD card might be in the process of writing and
you'll easily corrupt it. Make sure you always run 'sudo shutdown -h now' or
something similar before powering down the Pi. I power up and down Pi's almost
every day and have never corrupted an SD card.

~~~
chisleu
This comes up every time someone mentions the corruption.

We don't power off our many pis, but they are on UPSs (we use them for a
security system.) However, the corruption happens so much that we keep disk
images and have a spare on hand when we have to reboot them for any reason
because 1/4 of the time they will not boot up.

Even if it were corrupting the FILES being written when hard booted, it
shouldn't corrupt the FILESYSTEM being written.

TLDR, nuh uh.

~~~
tdicola
> Even if it were corrupting the FILES being written when hard booted, it
> shouldn't corrupt the FILESYSTEM being written.

That's not how SD cards work unfortunately. When an SD card erases data, like
if it's updating a file allocation table, it has to erase an entire block of
flash and not just the bytes you care about. The card will throw the block
into a cache in memory, erase the block, and then rewrite the parts of the
block that weren't erased. However if you pull out power during that operation
you'll completely kill the block and destroy the filesystem.

There's a great video here from Linuxconf Auckland about using SD cards for
embedded systems and these issues:
[https://www.youtube.com/watch?v=K3zb6p0thQU](https://www.youtube.com/watch?v=K3zb6p0thQU)

~~~
mark-r
I wish we had a filesystem that was tuned to the peculiarities of flash
memory. It should be aware of the large erase blocks and optimize for that.

