MceraWV
Posts: 5
Joined: Mon Sep 30, 2013 8:42 pm

LCD screen power options?

Sat Dec 21, 2013 12:44 am

Hello,

For the past few weeks, I've been dying to make my Pi portable.
I've checked and double checked all of the parts I'd need, and keep getting smacked in the face by the same problem: the LCD screen.
I'm going for this one: http://www.adafruit.com/products/912

However, the specifications say that it requires 6-15V DC.
I'm aware that your average USB port outputs about 5V, which was a big disappointment that I'm one volt short of powering the screen.

So far, I've only found three ways to power the screen:
1. Get two SEPERATE power supplies (one for the Pi and one for the screen).
2. Use a 12V power supply, splice it, and get a voltage regulator for the Pi.
3. Power the LCD from the Pi's GPIO pins.

I would prefer the third option, but I have no idea where to start, and haven't seen it done at all except here: http://www.raspberrypi.org/phpBB3/viewt ... 38#p175038
I'm as much as a beginner at this stuff as one can be, so I would appreciate any help at all :D

Thanks in Advance!
-Mc

User avatar
Tage
Posts: 287
Joined: Fri May 24, 2013 2:29 am
Location: St Thomas, Ontario Canada

Re: LCD screen power options?

Sat Dec 21, 2013 1:14 am

it seems that the display is using a buck-regulator that operates from 6V minimum. this indicates that the output voltage is 5V, so if you manage to find the schematic for the board you may be able to figure out where to connect 5V from the Pi. you may have to remove the input capacitor to the buck regulator, or the entire regulator.

klricks
Posts: 6609
Joined: Sat Jan 12, 2013 3:01 am
Location: Grants Pass, OR, USA
Contact: Website

Re: LCD screen power options?

Sat Dec 21, 2013 6:19 am

I would go with your option 2 but use a switching or 'buck' type regulator, not a linear 7805 etc.
The RPi will not likely have enough power to run that screen from the GPIO as your are limited to about 750mA by the main fuse F3. The RPi w/ keyboard and mouse will take most of that (500-600mA) or so. (The specks for the display says 150mA for 6V).

Also the screen is composite. If you have not used composite then I would suggest, before you buy the screen, try composite on an old TV. IMO the composite's is not really usable....... low resolution, text jitters, is blurry and hard to read etc.

I would look for a portable HDMI screen instead. Maybe something like this:
http://www.ebay.com/itm/Diy-Monitor-for ... 1c334f8a0f
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

ZacharyIgielman
Posts: 101
Joined: Sun Dec 08, 2013 11:27 am
Location: London

Re: LCD screen power options?

Sat Dec 21, 2013 7:05 am

MceraWV wrote:Hello,

For the past few weeks, I've been dying to make my Pi portable.
I've checked and double checked all of the parts I'd need, and keep getting smacked in the face by the same problem: the LCD screen.
I'm going for this one: http://www.adafruit.com/products/912

However, the specifications say that it requires 6-15V DC.
I'm aware that your average USB port outputs about 5V, which was a big disappointment that I'm one volt short of powering the screen.

So far, I've only found three ways to power the screen:
1. Get two SEPERATE power supplies (one for the Pi and one for the screen).
2. Use a 12V power supply, splice it, and get a voltage regulator for the Pi.
3. Power the LCD from the Pi's GPIO pins.

I would prefer the third option, but I have no idea where to start, and haven't seen it done at all except here: http://www.raspberrypi.org/phpBB3/viewt ... 38#p175038
I'm as much as a beginner at this stuff as one can be, so I would appreciate any help at all :D

Thanks in Advance!
-Mc
Could you tell us about your battery power supply for the pi, and hopefully what we are going to have to make work with the screen? What voltage? Up to how much current (if limited)? How does it output (USB, just pin connectors etc)? If USB, how many outputs?
Don't be mean, I'm only fifteen :D

MceraWV
Posts: 5
Joined: Mon Sep 30, 2013 8:42 pm

Re: LCD screen power options?

Sat Dec 21, 2013 1:05 pm

Tage,

Yeah. I read somewhere that for a monitor someone got off of Amazon (http://www.amazon.com/3-5-Inch-TFT-Moni ... B0045IIZKU) they had to open it up and re-solder something... It seems like if I wanted a non-regulator solution, this would be my only option. Worrying that I would render the display useless however, I'm not completely sure about attempting that.

klricks,

I have used composite before, and I've thought about that issue with the text. The only reason I wasn't going with HDMI was due to the large price tag of HDMI monitors. I'll definitely look into that more, and see if I can't find a composite screen that would be nice. If not, then I think I'll take your advice about a small HDMI-compatible display.

Zacharylgielman,

The battery supply I was looking for was this one through Amazon: http://www.amazon.com/PowerGen-External ... _sim_cps_3 I was originally going for the 1-port version, but I was afraid that splicing one USB cable wouldn't provide enough power. According to the page, output is "DC 5.3V / 2000mA and DC5.3v / 600mA".

Just out of curiosity though, how did the person in the link from my original post manage to power HIS display from the Pi's GPIO pins?

Thanks again!
-Mc

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