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

Posted: Sun Aug 04, 2013 11:09 am
by dasimpson
I did my monitor so that was 5 volt out to usb that way I could run the screen on a 12 volt battery and the reg in the lcd ran the pi

I wish they would make a screen already that an add on for the pi you know you just slot it on top like you do the expansion boards

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

Posted: Sun Aug 11, 2013 3:15 pm
by blc
Hey

Just wanted to say thanks for the idea! I have a very similar 3.5" composite LCD that I've had kicking round for years; I managed to get it to run on a minimum of 6v with no modifications, so I'd been planning to use a separate 6v rail to power my screen until now...

Popped it open and traced the power input to to an MP1410ES DC-DC converter. Found the datasheet for it and I managed to identify the GND and switched 5v output pins; hooked up a seriously bodged 5v supply directly to those pins and it works just fine :).

I noticed some power consumption figures on the first page or so of this thread, so I'm going to assume a maximum of 500mA draw on the screen - hopefully it won't actually be that high - which will be 2.5W. With a Model A Pi, theoretically my whole setup should draw 3.5W tops (500mA for the screen, 200mA for the Pi)... My project will be running from a 3.7V LiPo cell feeding a 5V boost converter; assuming a 3Ah battery and 70% boost efficiency, that's a theoretical maximum of 7.7Wh at the battery - around 2hrs of runtime, so not bad :)

Very tempted to go up to a 4.3 inch screen now! :)

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

Posted: Sun Aug 11, 2013 4:14 pm
by dasimpson
I can tell you now that the 3 volt boost circuit will be doublthe current draw as the pi and screen pulls when I had my screen and pi on they were pulling upto 500mah the draw from the battery was close to an amp

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

Posted: Sun Aug 11, 2013 4:17 pm
by dasimpson
the best thing I found was using 3 li-ions in series and using a ubec 2000mah at 11.1 volt give about 6 hours + run time

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

Posted: Mon Aug 12, 2013 1:49 pm
by blc
I guess it all depends on the efficiency of the buck/boost converter in question. I've got a couple of boost converters on their way from China which claim up to 92% efficiency; I don't believe that for a second, so I'm assuming a worst-case scenario of 70% efficiency.

Of course I won't know the actual values until I get my order through and start testing :).

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

Posted: Sat Aug 24, 2013 4:34 am
by jordan314
I have the same display as Kronalias. Thanks for your video Kronalias.
I saw a comment by Patrick on this blog (http://www.wisegai.com/2012/11/29/raspb ... using-usb/ ) that says he connected a 2S 7.4v lipo to the display, and it was enough voltage even through the DC to DC voltage converter chip to power the display. So I tried connecting my 2S 7.4 lipo (actually 8.5 v charged) directly to the display, and I blew the fuse in the cable, which is rated at 1A 250V. My display still works if I bypass the fuse with my 12V AC adapter. My questions are:
If I bypass this fuse with the lipo will I fry my display?
If yes, how can I lower the current to under 1A?
I have a 5.2V voltage regulator for the lipo which works well with a strand of LED lights. Do you think I can power the display, regulator and lights all with one lipo?
Thanks,
Jordan

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

Posted: Thu Sep 12, 2013 6:35 pm
by Andrie
e21c wrote:Finally, i have got working display
Image
How did you connect it in your usb memory stick?

- Regards,

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

Posted: Thu Oct 24, 2013 11:57 pm
by irononreverse
Hi, I've bought one of these but I haven't seen this circuit yet. it's a lot more compact. Does anyone know if it can accept 5v input?

Image

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

Posted: Tue Nov 05, 2013 7:54 am
by selorami
irononreverse wrote:Hi, I've bought one of these but I haven't seen this circuit yet. it's a lot more compact. Does anyone know if it can accept 5v input?

Image
Sorry for a late reply.
Yes, you can modify that to work with 5V instead of 12V. That IC with eight legs in the left side of the pcb is a buck-converter used to generate 5V. If you have a multimeter, you can measure voltage of the "10v 470uF" capacitor while the board is powered... It should show 5v.
One way to do this mod is to cut the trace going from inductor marked with "680" to capacitor marked with "10v 470uF" with fe. a exacto knife and solder power cable (positive) to the upper leg of the capacitor.
Remember to make the cutting carefully: you want to make small gap there, but you don't want to cut any other traces.

This tip is based on that image and a datasheet of td1509p5 buck-converter. If this mod works, thats good... that is what should happen. If you get nothing on screen after this mod, take the power off quickly and check for any shorted traces near the places you have worked on. I take no responsibility for any damage you do to your device.

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

Posted: Thu Nov 07, 2013 1:02 am
by thedishwasher
Yet another board design (for the 3.5" screen)

Image
Image
Image

I went with the previosly posted method and it works flawlessly.

my config.txt is slightly different though

Code: Select all

overscan_left=20
overscan_right=20
overscan_top=-20
overscan_bottom=-25

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

Posted: Thu Nov 14, 2013 11:40 am
by coolcrab
I also have a new board, however this one does not have a 5v pin so I'm a bit afraid to so things with it. =/

It does have a 3.3v pin though (on the back)
Image
Image

Any suggestions as to how I wire it?

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

Posted: Fri Nov 15, 2013 9:40 am
by coolcrab
My scientist friend helped me :D
Image
Image

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

Posted: Sat Jan 11, 2014 6:44 am
by sgrobben
Thanks to all for the info in this thread I was able to easily modify my display to run on USB. No components removed and used the original cable.
image3044.jpg
image3044.jpg (54.32 KiB) Viewed 7943 times
Probably didn't need to move that ground wire, but it just seemed like the right thing to do at the time :)

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

Posted: Thu Jan 16, 2014 5:26 pm
by peterkaiser
Hi guys,
I recently ordered one of those Taotronics 3.5" monitors at Amazon. They now have a really compact PCB (which is really great since I destroyed one when trying to fit it in another enclosure) but I don't have a clue what I could solder around in order to make this thing working @ 5V. Did anyone of you solve the problem for this new PCB? Appreciate every hint (and sorry for the bad pic quality) :)

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

Posted: Fri Jan 17, 2014 5:38 pm
by blc
peterkaiser wrote:Hi guys,
I recently ordered one of those Taotronics 3.5" monitors at Amazon. They now have a really compact PCB (which is really great since I destroyed one when trying to fit it in another enclosure) but I don't have a clue what I could solder around in order to make this thing working @ 5V. Did anyone of you solve the problem for this new PCB? Appreciate every hint (and sorry for the bad pic quality) :)
There was no obvious 5v input on my 3.5" LCD either, so the way I did this on my screen was to first see whether there's any regulators on there; I then tied in 5v power to the 5v output of the regulator and bypassed the 12v power input altogether. Note: I am not an electronics engineer (though I can read a data sheet and design a schematic) so this might not be the best way to do it and there is no guarantee that this will not fry something - your mileage may vary, and on your head be it if you kill something :)

There are a couple of 8-pin devices on there (either side of the big quad flat-pack chip) that could be switching regulators; google the model numbers on them to see if you can find the data sheet. There's also a 3-pin device (bottom-left) which could be a linear regulator; I think it's more likely that it would use a switching regulator, but I could be wrong. If I had to hazard a guess, I'd say that the 8-pin device on the left-hand side of the board is a likely candidate for a switching regulator (if there is a 5v regulator on there at all); it looks like there's an inductor over on that side, which is a good bet that there's power stuff over there.

I'd start by finding out what those three devices are and then tracing out where the 12v input goes.

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

Posted: Fri Jan 17, 2014 6:08 pm
by peterkaiser
blc wrote:
peterkaiser wrote:Hi guys,
I recently ordered one of those Taotronics 3.5" monitors at Amazon. They now have a really compact PCB (which is really great since I destroyed one when trying to fit it in another enclosure) but I don't have a clue what I could solder around in order to make this thing working @ 5V. Did anyone of you solve the problem for this new PCB? Appreciate every hint (and sorry for the bad pic quality) :)
There was no obvious 5v input on my 3.5" LCD either, so the way I did this on my screen was to first see whether there's any regulators on there; I then tied in 5v power to the 5v output of the regulator and bypassed the 12v power input altogether. Note: I am not an electronics engineer (though I can read a data sheet and design a schematic) so this might not be the best way to do it and there is no guarantee that this will not fry something - your mileage may vary, and on your head be it if you kill something :)

There are a couple of 8-pin devices on there (either side of the big quad flat-pack chip) that could be switching regulators; google the model numbers on them to see if you can find the data sheet. There's also a 3-pin device (bottom-left) which could be a linear regulator; I think it's more likely that it would use a switching regulator, but I could be wrong. If I had to hazard a guess, I'd say that the 8-pin device on the left-hand side of the board is a likely candidate for a switching regulator (if there is a 5v regulator on there at all); it looks like there's an inductor over on that side, which is a good bet that there's power stuff over there.

I'd start by finding out what those three devices are and then tracing out where the 12v input goes.
Thanks for the hint. I just removed the PCB from the glue pad and found a "+5V"-spot on the backside. Looks like it is connected with a capacitor. I try to solder it there - What could possibly go wrong? :D

Edit: Didn't work - it just triggered the LCD back-light but no image on screen :(

Edit 2: It works \o/ The ribbon cable wasn't properly mounted. now the monitor works @ 5V :)

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

Posted: Sat Jan 18, 2014 9:57 pm
by HoiPim
i modded a pi and make the screen and pi work as one.
Image
Image
Image

I can't show you how i dit it. I deleded the photo's. Sorry :cry:

Pim

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

Posted: Wed Jan 22, 2014 11:34 am
by hlotac
Hi, i recently got my 3.5" display, and to my surprise the board is different from all of these. Only one is slightly similar, but nevertheless different.

Are there some electronic savvy people here that can identify where i should solder on my PCB?

Image
http://i.imgur.com/KHaZItB.jpg (large)

I saw somewhere that i could just measure the capacitors for 3.3, 5 and 12V, and solder the usb to ground and the 5V side of the 5V capacitor.. Please correct me if i am wrong.

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

Posted: Thu Jan 30, 2014 3:54 am
by sgrobben
Hlotac,
Not sure if you already have your LCD sorted, but in your pic there is a rectangular 8 pin chip in the lower left corner labeled ACT4060A. This is a step down converter where your input voltage is being converted to the appropriate voltage (hopefully 5v). Check out the data sheet for that chip and see if you can probe the output for 5v and possibly power your board there. Also, check the grouped open pads on the board (while powered up) that's where it seems many of these boards have an easy way to add your 5v line.

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

Posted: Thu Jan 30, 2014 11:09 am
by hlotac
I just soldered onto the C74 capacitor and it worked with a 5V input.

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

Posted: Tue Feb 04, 2014 7:58 pm
by bpm009
I tried soldering onto the positive side of the capacitor, but when I go to power the screen, I get a quick flash of the screen and then it goes back. I've tried playing around with a few 5v spots on the PCB but its the same quick flash then black each time. Anyone have any ideas as to what might be the cause?

http://imgur.com/izP3vLV

I removed the 8 legged monster (1) which is apparently the step down from 12v to 5v. Then I tried using the original power in location which showed no promise. Next, leaving the ground at (2) I tried some above advice and tried using the capacitor positive lead to get my 5v power at (3). To my surprise the screen lit up..... then instantly went black again. I'm thinking I'm getting close but am unsure how to proceed because I've run out of ideas.

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

Posted: Mon Feb 10, 2014 8:42 pm
by peterkaiser
If the display flashes, it's normally a good sign (at least it was when I did some experiments with my 2 different PCBs) - The reason why it switches off instantly might be because you haven't connected a video input (eg. RPI S-Video). Pls try it again with your full setup (Display connected to USB the way you described it so that it flashes; RPI connected to Display with RCA cable).

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

Posted: Thu Mar 06, 2014 7:25 pm
by nerd7473
http://www.ebay.com/itm/RCA-DRC69702-Po ... 126wt_1224

How do I use the screen that has composite input with 5 volt input. I need help with this as I am trying to make my raspberry pi portable. The screen I am going to use has a 9v to 12v input at 1a and it has a max of 2.5a. I am going to use a two port usb battery to power the raspberry pi and the screen. I would also like to say that the screen is not the one pictured in the link, though similar.

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

Posted: Fri May 16, 2014 6:36 am
by thak
Hi!

I recently bought a car display, and like all of you, i'd like to run it on 5v.
But the pcb seems to be completly different from the one you've already post.

Image

Image

Could someone help me to run this one on 5v if possible?
Thanks a lot!

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

Posted: Tue May 20, 2014 7:10 pm
by Stuupy
Hi all,
Thak, I have just opened my display, and it is the same as yours.
Did you have any joy getting this to run on 5v, as I am stumped.
Anyone else seen this display?