AndyA
Posts: 31
Joined: Mon Sep 17, 2012 6:02 pm

Re: Modifying a 3.5" car display for USB power.

Tue Oct 16, 2012 3:09 am

However my control board is unlike yours, any idea which is the 5v resistor.
The main regulator will be the bigger part in the top right. The 5V rail will go to one of those 3 large capacitors on the right,
which one is impossible to tell from that photo.
If you have a voltmeter it should be possible to work out which one. Failing that you may be able to tell by looking closely at the traces on the board.
The two 4 pin parts to the left will then regulate down from 5 to probably 3.3 and 2.5
Also the wires in the cord are not of the same color as in your tutorial and would appreciate if anyone could tell me which are for the video feed.
Again looking at the board is the best bet. From the connector one pin will go to a thick trace, that's the 12v power in. One will go to a large copper area, thats ground. And the other two will be thin lines going to some small resistors near that big square chip, they are the two video inputs.

On another note, does anyone know how to wire a 4 port usb hub directly to the pi, so I dont have to have it taking up space on the usb ports
If it was connected like that you wouldn't then be able to use that port. You can bypass the current limit protection on the ports so that you can power more things directly if your power supply has enough power but what you want would only save you the plug sticking out, you wouldn't gain any ports.

Krebsy
Posts: 10
Joined: Thu Sep 20, 2012 2:55 pm

Re: Modifying a 3.5" car display for USB power.

Tue Oct 16, 2012 9:53 am

For the screen, the best option is to wire up 8 AA batteries in a holder to the red and black feeds for the screen, then take the back off and probe against any of the exposed capacitor legs with a voltmeter. When you find +5v, that's the spot to attach the power feed to.

Likewise, when connecting up the batteries, measure the voltages on the back of the connector where the cable comes in and attaches to the motherboard. The +12v you detect "should" be the red cable on the left and that'll be the one to pull out of the block and splice to the capacitor leg....

DFog
Posts: 3
Joined: Fri Aug 24, 2012 12:12 am

Re: Modifying a 3.5" car display for USB power.

Wed Oct 17, 2012 1:17 am

AndyA wrote:Snip
Thank you for your response. I believe I solved which wires are the video input. What I am unsure of is do I need to take out one of the cylindrical capacitor. I don't really care if I lose use of one of the usb port of the board as long as the 4 port hub connects in its place. I am constructing a case mod with very limited room and can not have the wire sticking out of the case only to be routed back into the hub Additionally, is there a way to power this screen off of the pi itself without taking a usb port?

AndyA
Posts: 31
Joined: Mon Sep 17, 2012 6:02 pm

Re: Modifying a 3.5" car display for USB power.

Wed Oct 17, 2012 1:31 am

DFog wrote: However, what I don't understand is what do you mean by the 4 pins to the left? ... Additionally, id there a way to power this screen off of the pi itself without taking a usb port?
I mentioned the two 4 pin parts on the left. They have 3 small pins on one side and one large one the other. These are linear voltage regulators used to drop a power supply from one voltage to a lower one. Not very efficient but simple and fine for smaller drops.

You can power the screen from the pi but you would need to solder the power connection directly to the pi board before the fuse on the power input, all of the headers are after the fuse and so couldn't be trusted to supply enough current. You would also need a power supply able to source sufficient power for both.

eyebee
Posts: 35
Joined: Tue Sep 25, 2012 7:05 pm
Location: Los Angeles, CA

Re: Modifying a 3.5" car display for USB power.

Wed Oct 17, 2012 6:26 pm

I see three models on the Amazon US website that are about $18. The product photos look slightly different and there are no photos of the packaging so I am not sure if all have the same internals or not. Could someone who made this hack work with a product they bought on Amazon let me know which is the screen to order?

Option 1 $17.99
Option 2 $19.70
Option 3 $18.45

Thanks.

AndyA
Posts: 31
Joined: Mon Sep 17, 2012 6:02 pm

Re: Modifying a 3.5" car display for USB power.

Wed Oct 17, 2012 8:54 pm

eyebee wrote:I see three models on the Amazon US website that are about $18. [...] Could someone who made this hack work with a product they bought on Amazon let me know which is the screen to order?

Option 1 $17.99
Option 2 $19.70
Option 3 $18.45

Thanks.
I've opened up both 1 and 3 and they are identical.
I haven't tried 2 but I'd be willing to bet that it too is the same internally.

eyebee
Posts: 35
Joined: Tue Sep 25, 2012 7:05 pm
Location: Los Angeles, CA

Re: Modifying a 3.5" car display for USB power.

Wed Oct 17, 2012 9:37 pm

Great! Thanks for the info.

jonty
Posts: 2
Joined: Sat Oct 20, 2012 4:06 pm

Re: Modifying a 3.5" car display for USB power.

Sat Oct 20, 2012 4:17 pm

It seems like there are many different board revisions out there, and I have one that nobody has documented before.

Image

The screen works fine when powered from 12v, but tapping into any available 5v points (including the spare through-hole connectors) results in a white screen and nothing else. It does switch on and off when the video feed is connected, so it's operating on a basic level, but nothing else works.

Has anyone else suffered this, or does anyone have any ideas about how to tackle the problem?

[email protected]
Posts: 39
Joined: Thu May 31, 2012 8:04 pm

Re: Modifying a 3.5" car display for USB power.

Tue Oct 23, 2012 12:30 am

Hiya

I have yet to make the mod, just preparing everything software wise before I mess with the wiring and put this in the car

I have got my 3.5 inch screen working, and modded the config.txt, and the display is looking great from the command line. The trouble I am having is that when I go into x and launch an xterminal the xterm window boundaries are outside the actual borders of the screen. I need to know how I can modify the xterm preferences to make it display correctly.

Part of my usage for this pi in the car will be using xterm to capture input, and I need the xterm to be displayed correctly.

Obviously I will be sharing details of my in car application (an integrated music, video, karaoke, slideshow and hopefully sat-nav system) when it is complete.

Cheers
Matt

Michael Meissner
Posts: 48
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Contact: Website

Re: Modifying a 3.5" car display for USB power.

Tue Oct 23, 2012 5:06 am

Well if you read the man page for xterm, it discusses the -geometry option which gives the rows and columns. Most of the -f options control the various fonts. The XTerm*vt100.geometry resources control the geometry and position of the vt100 box for generic xterm's, while <name>*vt100.geometry controls box size for a specific named xterm (replace <name> with argument used in the -name command line).

aaa801
Posts: 428
Joined: Mon Jun 04, 2012 9:06 pm
Location: Berkshire

Re: Modifying a 3.5" car display for USB power.

Wed Oct 24, 2012 9:34 am

jonty wrote:It seems like there are many different board revisions out there, and I have one that nobody has documented before.

Image

The screen works fine when powered from 12v, but tapping into any available 5v points (including the spare through-hole connectors) results in a white screen and nothing else. It does switch on and off when the video feed is connected, so it's operating on a basic level, but nothing else works.

Has anyone else suffered this, or does anyone have any ideas about how to tackle the problem?
I had this board, i totaly fried it tho =/

AndyA
Posts: 31
Joined: Mon Sep 17, 2012 6:02 pm

Re: Modifying a 3.5" car display for USB power.

Wed Oct 24, 2012 4:00 pm

jonty wrote:It seems like there are many different board revisions out there, and I have one that nobody has documented before.

Image

The screen works fine when powered from 12v, but tapping into any available 5v points (including the spare through-hole connectors) results in a white screen and nothing else.
Does the big regulator in the lower right generate other voltages in addition to 5? If so that could explain it.

jonty
Posts: 2
Joined: Sat Oct 20, 2012 4:06 pm

Re: Modifying a 3.5" car display for USB power.

Wed Oct 24, 2012 4:10 pm

AndyA wrote:
jonty wrote:It seems like there are many different board revisions out there, and I have one that nobody has documented before.

Image

The screen works fine when powered from 12v, but tapping into any available 5v points (including the spare through-hole connectors) results in a white screen and nothing else.
Does the big regulator in the lower right generate other voltages in addition to 5? If so that could explain it.
This is the regulator, it seems to just be a 12v->5v thing, which my probings agree with: http://datasheet.seekic.com/pdfimage/1CZ/1CZ41Hpdf0.jpg

bonesai
Posts: 11
Joined: Thu Oct 25, 2012 1:42 pm

Re: Modifying a 3.5" car display for USB power.

Thu Oct 25, 2012 1:50 pm

Thanks - this worked like a dream - well on the way to building a PiBoy300 now :)

Plus i got this screen from Amazon for £13 inc p&p !

Now for a noob question. I have the screen running off of 4 AA batteries. If I want to run the Pi off of the same battery block, is 4 enough (6v), or do i need more? I'm assuming 4 is ok, but they will drain fast so such use the best rechargables i can get (i have some rated at 2300xxx running the kids' lego power functions that I'll borrow). Or do I need two separate sets of 4 and run the devices separately?

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dasimpson
Posts: 311
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Re: Modifying a 3.5" car display for USB power.

Mon Nov 12, 2012 6:51 pm

i have the same pcb as jonty and i also get the white screengoing to try and remove the reg see if that changes anything

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dasimpson
Posts: 311
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Re: Modifying a 3.5" car display for USB power.

Mon Nov 12, 2012 7:27 pm

removing the regulator did not help still the white screen on another note i ran thr rpi from the regulator as well as the screen and they both work just meani have to run 18650 li-ions in sreies for the 7.4 volt
not how i wonted to run as this more then halfs my run time with the 4x 5amp hour li-ions i have but i do have a 3v to 5-6v dc-dc boost converter so we will see how that goes

kobzar
Posts: 37
Joined: Tue Jul 17, 2012 1:09 pm
Location: Ukraine

Re: Modifying a 3.5" car display for USB power.

Tue Nov 20, 2012 6:21 am

Great !
Just do it for 5 minute, an all is working fine.
Thanks for this manual!!! It's realy good solutions !
No Fate!

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dasimpson
Posts: 311
Joined: Fri Jun 29, 2012 2:17 pm

Re: Modifying a 3.5" car display for USB power.

Tue Nov 27, 2012 11:06 pm

could some one pls send me to a link for a screen like these that is 640x480 and works on 5volt pls thank you

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dliloch
Posts: 168
Joined: Wed Jun 27, 2012 6:28 pm
Location: cleveland, ohio usa

Re: Modifying a 3.5" car display for USB power.

Sat Dec 08, 2012 6:48 pm

thanks for the great instructions.. I converted my display today from 12v to 5v. I first tested it
off my duracell lithium battery and it worked perfectly... then I tried a usbport on my intel
linux box .. ok .. finally I tried plugging it into the raspberry pi itself.. but I only get a completely
white screen... what is happening here? I only used the red and black as you indicated.. my
usb cord did not have a ground shield .. could that be the problem .. worse case I'll just plug in
into the usb converter directly ...

thanks

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dasimpson
Posts: 311
Joined: Fri Jun 29, 2012 2:17 pm

Re: Modifying a 3.5" car display for USB power.

Sat Dec 08, 2012 9:08 pm

no the problem here is the raspberry pi can not supply the voltage and current needed
to run the screen to need to connect the screan to the gpio pin for 5v and ground supplying one amp into the pi will take about 700ma leaving about 300 for the screen

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dliloch
Posts: 168
Joined: Wed Jun 27, 2012 6:28 pm
Location: cleveland, ohio usa

Re: Modifying a 3.5" car display for USB power.

Sun Dec 09, 2012 3:43 pm

so it is definitely a power issue.. by the way the rev 2 board on the raspberry pi does power the
screen but it is choppy .. goes black between displays.. so I'm using a powered hub .. I was always wondering what good the rca output was .. and now I see..

AndyA
Posts: 31
Joined: Mon Sep 17, 2012 6:02 pm

Re: Modifying a 3.5" car display for USB power.

Sun Dec 09, 2012 4:06 pm

You can power the display from the pi mk. 1 but you need to modify the board by tieing the power input directly to the usb power outputs.
Bypassing the current limit protection isn't a good idea most of the time, it's there for a reason, but isn't hard to do if you need to save the space a hub would take up.

Liuqahs15
Posts: 21
Joined: Sun Nov 18, 2012 4:17 am

Re: Modifying a 3.5" car display for USB power.

Tue Dec 11, 2012 12:50 am

Just for clarification, what is the name of that USB power source you've got the screen plugged into in the final image? I'm interested in some power sources to power a little portable pi computer.

Thanks.

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dasimpson
Posts: 311
Joined: Fri Jun 29, 2012 2:17 pm

Re: Modifying a 3.5" car display for USB power.

Tue Dec 11, 2012 12:54 am

i myself use a few old 18650 from dead laptops and i use this to take the 3.7 upto 5 volt at 1 amp http://www.ebay.co.uk/itm/121032595157? ... 1423.l2649

i have modifyed my rpi into a old gameboy

jhedmonton
Posts: 3
Joined: Thu Dec 06, 2012 3:47 am

Re: Modifying a 3.5" car display for USB power.

Wed Dec 12, 2012 2:34 am

Hi Andy,
would you have a URL for the display? Maybe I am missing something, but the posts start with a reference to a display but there appears to be no link or even model description.
Thanks!
Johannes

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