Modifying a 3.5" car display for USB power.


182 posts   Page 4 of 8   1, 2, 3, 4, 5, 6, 7, 8
by AndyA » Fri Jan 18, 2013 2:18 am
I think most work on about 5.25V, exactly where below that point they stop will vary board to board even for ones of the same design.
The point of making the changes is to work from any USB voltage and also drop the current draw, running a switching regulator to convert 5 volts to 5 volts isn't very efficient when it's designed for a 12 volt input.
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by dooblem » Fri Jan 18, 2013 8:17 am
Well, but I don't know another way to make it work on 5v. Any other idea?
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by AndyA » Fri Jan 18, 2013 4:43 pm
dooblem wrote:Well, but I don't know another way to make it work on 5v. Any other idea?


Sorry, not much help I can give without access to the circuit to poke around a bit.
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by AndyA » Mon Jan 21, 2013 7:35 pm
Two more board reworks, both of these will convert the existing input cable to 5V input.
Note: outwardly there is no indication that the display is modified but connecting it to 12V will blow things up so if you have more than one display around make sure to mark it clearly.

First a different board found in exactly the same display as the original rework (a 3.5" car backup camera display from amazon for $18).
The display board looks like this:
Image

Remove the part marked with an X (the switching voltage regulator).
Optionally remove the 3 parts marked R (two inductors and the 12V capacitor).
Connect a wire from point 1 (either the inductor or the diode, which ever is easiest to solder to, not both) to point 2.


Secondly this is the board from a 4.3" wide screen car backup display ($22 from amazon):
Image

Remove the part marked X (the switching voltage regulator).
Connect a wire as indicated by the red line. The 12V input pin on the connector (the one furthest from the edge) to the 5V pin of the 4 holes in a line at the edge of the board near the input connector (the one nearest the input connector).



And finally a word of warning. On the top display I was using a hot air gun to remove the IC and in order to avoid melting the input connector I was angling the heat away from that area. Just as the part was starting to lift this happened:
Image
The body of the cap hit my chest with a lot of force for something that small, if it had hit my eye (and I wasn't wearing glasses) that could have been a nasty injury. As you can see it also knocked a couple of parts clear off the board.
So 1) be careful when using hot air guns and 2) it's probably best to remove the board from the display panel when doing this work (I was lazy) and 3) don't let me near your electronics ;-)
After a brief clean up the display still works fine.
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by dasimpson » Tue Jan 22, 2013 4:46 am
i found meltiong solder across all pins of the chip and lifting with a stanly knife edge to be the simpler way
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by AndyA » Wed Feb 06, 2013 7:23 pm
OK. Warning note about the 3.5" board two posts up.

That board runs some parasitic voltage doublers and inverters off the main switcher in order to generate LCD bias voltages required by certain display panels.

Or in english - Depending on the exact display panel used in the unit you got it may not work from anything other than ~12 volts. A universally working rework for 5V operation is going to be complicated.
I ordered 3 displays from the same supplier and got 3 slightly different sets of internals so there is no way to be sure what you're going to get.


I'm still trying to decide if this is a sign of a very smart and efficient design or a very sloppy cheap hack of a design.

Since the bias voltages generated vary depending on the supply voltage and automotive supply voltages are all over the place I'm tempted to go with it being a sloppy hack but it's still a good cost saving trick.
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by e21c » Wed Feb 06, 2013 10:47 pm
I bought very similar display and I modified it as presented below. I assumed that there is a circuit similar to this one attached to XL1509-5.0 datasheet. Additionally, I didn't cut off any path or remove any element so my display may be powered from 5 or 12 V sources.
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by e21c » Wed Feb 06, 2013 10:48 pm
Finally, i have got working display
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by dasimpson » Wed Feb 06, 2013 10:49 pm
also you can put 12v into screen and power the pi thru usb from the screen you could of also connected the screen to the 5v gpio pin thats how mine runs
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by themuffinman » Thu Feb 07, 2013 9:12 am
Wully wrote:I redone it and wired the red wire to the 5V header. Connected a video input and a USB to DC cable and it worked perfectly!
Image
Thanks for the great guide and the extra help!
Image


I was just wondering how you actually soldered the usb cable to this. Did you buy a video input and usb to dc cable or did you make your own, Could you give more details?
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by waltermixxx » Sun Feb 17, 2013 6:05 pm
I have a similar 3.5" LCD panel (no switches on it), also for automobile applications. However this one will accept voltages as low as 5.0 volts. I made a USB to power adapter so I can plug the monitor via USB into my raspberry pi, along with a usb wireless keyboard/mouse dongle all from a blackberry phone power adapter....

I tweeted about it just now... Same name on twitter Waltermixxx.

The little chip that the original poster removed, at least in my case did not have to be removed....

Infact I did not have to mod it at all, I just built a short USB to 2.1mm jack as shown in my tweet... Happily running x and scratch. I will leave it on for a while and check for any melt downs....


Thanks to the original poster for introducing the idea which lead me to a solution that worked for me....

Now I just have to adjust the text size.

Cheers....
Electronics for fun...
Raspberry Pi-1 Occidentalist, Tenda 311m x 2
Raspberry Pi-2 Raspbian Wheezy 07-15-12, Netgear N150 x1
Genius 8000 slimline wireless keyboard and mouse both work great with the usb wifi dongle right in the raspberry pi.
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by waltermixxx » Sun Feb 17, 2013 6:53 pm
Hmmmm.... someone above mentioned powering the Raspberry pi off the display instead....

I actually like the sound of that better....
that way I have 2 free usb ports...
one for keyboard and one for wireless Tenda 311 wifi dongle... :)

hmmmmm.... i do like that...
Electronics for fun...
Raspberry Pi-1 Occidentalist, Tenda 311m x 2
Raspberry Pi-2 Raspbian Wheezy 07-15-12, Netgear N150 x1
Genius 8000 slimline wireless keyboard and mouse both work great with the usb wifi dongle right in the raspberry pi.
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by waltermixxx » Sun Feb 17, 2013 7:52 pm
Here is the Raspberry Pi powered by 5 volts grabbed from the 3.5" LCD monitor. ( used a micro usb power adapter and chopped the cable so it was not too long )

Image


Here is the Raspberry Pi powering the 3.5" LCD via the pi's usb cable. I built a USB to Power Plug cable to power the LCD from a 5 volt usb source.... no modifications done to the 3.5" lcd.

Image

you'll notice there is only one cable feeding both scenario's either 5 volts feeding the Rasberry Pi, and it feeding the monitor via usb, or one 10 volt cable feeding the LCD and a micro usb coming from it to feed the Rasbperry Pi... :) now if only the screen were a little larger... :)

cheers :) Both work fine and for a few hours with no issues thus far. :)
Electronics for fun...
Raspberry Pi-1 Occidentalist, Tenda 311m x 2
Raspberry Pi-2 Raspbian Wheezy 07-15-12, Netgear N150 x1
Genius 8000 slimline wireless keyboard and mouse both work great with the usb wifi dongle right in the raspberry pi.
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by dasimpson » Sun Feb 17, 2013 8:25 pm
they is some larher lcd that power from usb and get the graphics from usb as they have a built in graphics card but not sure if they would work because of drivers
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by CidVilas » Mon Feb 18, 2013 6:32 am
Here is my successful attempt. Follows the instructions everyone else has, but could help someone else. Thanks to all, who have contributed!

I've included pictures of the patch and post fix display. Works great, and minimal work done to the display.
IMG_20130218_002615.jpg
Jumper1
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IMG_20130218_002841.jpg
Complete
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by CidVilas » Mon Feb 18, 2013 2:48 pm
Here is the link to Amazon: http://amzn.com/B006MPRFJQ

And below is the Rasbian 'config.txt' settings:

Code: Select all
# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1
sdtv_mode=0

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
overscan_left=12
overscan_right=20
overscan_top=-26
overscan_bottom=-26

# uncomment to force a console size. By default it will be display's size minus
# overscan.
framebuffer_width=480
framebuffer_height=272
# END EDITED CODE

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL


#uncomment to overclock the arm. 700 MHz is the default.
arm_freq=1000

# for more options see http://elinux.org/RPi_config.txt
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by Kronalias » Fri Feb 22, 2013 4:12 pm
Here's a short video of my modded car display working with a Pi and Plugable usb hub:

http://www.youtube.com/watch?v=xhKaFuJ7A9o

The display came from eBay in the UK - here's the link:

eBay 3.5" TFT LCD
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by dasimpson » Fri Feb 22, 2013 4:45 pm
i belive you could of just shorted out the 12v pin and the 5volt pin on the chip
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by Kronalias » Fri Feb 22, 2013 9:11 pm
dasimpson wrote:i belive you could of just shorted out the 12v pin and the 5volt pin on the chip


Yup, but wouldn't that just be consuming extra power uselessly by keeping the 1509 IC powered up?
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by magno23 » Fri Feb 22, 2013 9:51 pm
can the raspberry pi be powered using the 5v line from the display?
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by dasimpson » Fri Feb 22, 2013 10:20 pm
no it bypasses the chp
yes you can power the pi from the 5 volt on the screen regulator
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by Andresv » Sat Feb 23, 2013 10:53 pm
What solder wire did you use or what type so I can buy some
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by dasimpson » Sun Feb 24, 2013 12:57 am
for doing what
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by Karamell » Sun Feb 24, 2013 2:09 pm
I did it similar without removing anything:

Image

The big advantage is, that you can do this without any advanced soldering skills. :)

The settings with:
framebuffer_width=320
framebuffer_height=240
overscan_left=-30
overscan_right=-30
overscan_top=-30
overscan_bottom=-30


worked very well for me, thanks for sharing this!
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by portablesounds » Wed Feb 27, 2013 1:21 am
@waltermixxx when i tried your power to usb cable my screen will only flicker for a millisecond, turn off, and repeat every few seconds. i think it may be due to the 5v to 12v regulator, considering power is coming through, or is it maybe bad soldering? My board is slightly different than everyone else's that has posted, but i believe i have found the correct converter, although my webcam is too crappy to give any good detailed photos. Hope someone has any idea as to what my problem is. Thanks! -portablesounds
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