Laptop made with 15.6" LCD screen and Raspberry Pi 3

[subwayheaven]

My project so far;



My project idea is essentially a portable laptop that is just an LCD screen with the raspberry pi and components strapped to the back (I have no idea how I would protect all the components, other than using a case for each or something similar).

I use an Amazon basic adjustable tablet stand to hold the LCD screen (does a good job too) and use Velcro strips to attach the Raspberry Pi 3 (in a case) to the back of the LCD screen.

I'm also hoping to get some sort of battery pack attached to the back of the screen.

I would be awesome if the whole set up only needed one power source, so far there is a 12v 5A DC Power adapter that plugs straight into the display board for the LCD screen. The driver board has HDMI as well as USB, I currently use the USB port to power the Raspberry Pi 3.

Unfortunately, although this works the 'Low power' symbol appears when I do intensive tasks (watching videos on a browser e.g.) and the performance of the Pi is quite slow.

Sooo, my question is; is this feasible or is the limiting factor going to the power output of the USB port on the display board? I've got a Power doctor (volt and amp measuring tool for usb) coming later today to see if the power coming out is anywhere near what I need for a raspberry pi 3.

[subwayheaven]

*shameless bump*

[lumsdot]

a 5v usb buck convertor should work


http://www.ebay.co.uk/itm/1pcs-USB-DC-7 ... 2ca48cb8f5:

give it 12volts and it will output 5v at roughly 3amps for the Pi

so you just need 12v taken directly from the display power supply and feed into buck convertor

[subwayheaven]

Thanks for the reply!

What I understand (I'm a complete newb), I can't plug the DC connector straight into the driver board for the LCD screen, but rather I need to have the DC cable plug into a DC connector on a PCB then have the power (12V) go to the driver board. Then also have the same 12V go into something like the step down buck you linked to get the 5V to power the raspberry pi 3.

Is that right?

I have some concerns such as how I would handle positive, negative and ground? Would I just soldier the DC barrel jack ( https://www.sparkfun.com/products/119) to a PCB via any of the jacks metal pins and that's all good? I feel like I'm missing something.

Thanks in advance

[lumsdot]

Just solder 2 wires to the driver board next to the 12v connector (ie underneath the connector), i.e. a 0v and 12v wire. You will need a multimeter to test for the 0v line. The 0v line is normally the outside of the 12v plug, the inside is the positive.

The 2 wires then goto the buck convertor, the convertor will have the 0v and positive input marked on the pcb.

This will slightly reduce the current available to the driver board, i.e. pi3 is about 1amp at 5volts so 5 watts. Since the buck convertor is running from 12v this will mean about a .5amp load will be taken for the pi 3, since .5 times 12v is about 6 watts.

If you find the 12volt 4amp power supply was getting too hot, with the extra load, you could maybe replace it with a bigger (higher current supply)

The brightness of the lcd screen may affect how much current the driver board needs.

[subwayheaven]

You mentioned how only .5amps would reach the raspberry pi 3? Why only .5amps? At the moment, the USB port on my display driver is only outputting .5amps (which isn't enough to fully power the Pi)

My DC power adapter gives 12V at 5A, I'm not too sure how much current the LCD screen is using, If I buy a multimeter I'll find out xD

[rpdom]

You mentioned how only .5amps would reach the raspberry pi 3?

No, about 0.5 Amps at 12V would be taken from the supply to be used for the Pi. The buck convertor will drops the voltage, but the output Amperage will go up by nearly the same proportion. If the Pi takes 1A at 5V, then the convertor will only need to take at max 0.5A at 12V to supply that. A little is lost in the conversion process.

[subwayheaven]

Ahh I understand, Thanks rpdom

[subwayheaven]

So I looked at the back of my driver board and found some mentions of 12V, one near the DC barrel jack and one near some pins I can't identify (they are unused and I'm wondering if I can connect some jump wire to them?)

The 12V near the DC barrel jack seems to be have 12V soldered together with ground, not sure why this would be done.

Sorry about being really brief and not having much to show you other than this picture of the DC barrel jack

[rpdom]

The 12V near the DC barrel jack seems to be have 12V soldered together with ground, not sure why this would be done.

The labels are referring to the set of four holes in the board, not the large lump of solder.

The holes are presumably for a 4-pin power socket to be fixed to, with the two holes nearest the edge of the board being +12V and the other two being 0V. Whether it is for power-in or power-out, I don't know.

[subwayheaven]

Sorry for the late reply, I finally got round to buying a multimeter and measuring the voltage at different points on the driver board.

The holes in the picture above turned out to give about 12.5V when I put the red wire at the +12 hole and the black wire at the ground hole.

So from my understanding, I could get some wire and solder to those 2 holes in the driver board and solder them to a step-down buck?

Is there any better way of doing this? Or is this the only/best way of doing it?

Cheers for all your help

[lumsdot]

That should work fine.
The step down to 5v board needs to be rated at 3 amps or more
Pi 3 takes a about 1 amp at idle , but this can increase depending on heavy tasks, and depending what you have plugged into pi 3 usb sockets.
The micro usb cable you are using to power the pi, should be a 2amp fast charge cable if possible, this has thicker wire.
cheap micro usb cables can drop a littlr voltage at high current.
Most new mobile phones support 2amp fast charge, and come with a 2a micro usb charge cable.

Some step down boards dont supply a perfectly clean 5v , so the better quality board you can get the better. But either way it should work

[lumsdot]

With my pi 3 portable , i am using 2 normal 5v usb portable powerbanks (6000mah each)
one to power the pi3 and one for my lcd driver board.

My lcd driver board needs at least 6 v to work, so i use a step up board from ebay to boost the 5v power bank to 6v for the lcd driver

Im using a 10ich lcd , so it does not need a high current

Your 15inch lcd may need more than 2amps, in which case you cannot use a powerbank, since most are rated at 2amps max

[subwayheaven]

Whoops...Just got a 2amp step down buck converter today. (https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1)

Does it need to be 3amp because of the power consumption of the pi 3? Or because of the combined power consumption of the LCD and pi 3?

I have no idea how much current the LCD uses.

I haven't soldered anything yet, so could I get away with using the 2amp? Or do I definitely have to use a 3amp? Can you explain how you figured that out as well so I understand for future reference

Cheers again

[lumsdot]

i think 3amps is needed, since that will be the max it can supply but only for a short period, so if it says 3amps you can assume it can do 1.5 amps no problem without burning up

the one you have does not have any large components on it, so may only be capable of 1 amp continous

this one below may be more upto the job, it has a large ic on it, so should handle the current better

http://www.ebay.co.uk/itm/7V-40V-to-5V- ... SwB4NWxMx7

plus one of the reviews for yours , said it burned out, so beware.

[lumsdot]

this one looks good also

https://www.amazon.co.uk/DC-DC-module-p ... own+supply

its adjustable, so means you could dial in 5.1 or 5.2 volts

pi3 is very fussy about low voltage, so even a 5 volt supply may not be enough to stop the low voltage warnings.

i think the offical pi 3 power supply is 5.1 volts

problem is you would need to be sure you dont have more than 5.2 volts selected as you could damage pi with too high a voltage

[subwayheaven]

Ordered the first one you recommended (no 'next day Amazon prime delivery', but oh well ).

I'm guessing there isn't much of a way to test the pcb without soldering it straight to my driver board? A little concerned I will solder it and then find out it doesn't work/the current is too low e.g.

[subwayheaven]

So I did it, I tested both of the wires coming out of the driver board using a multimeter and got a reading of 12.5V. Then I plugged my phone into the USB port on the buck converter and it charged!

I then connected it to my raspberry pi 3 and it booted and no longer gave me the power warning symbol at the top right of the screen (After I changed the cable to a different micro USB cable). I haven't actually read how much power the Pi is drawing yet, I'm just happy I do not get any power warnings anymore.

However, the reason I did this was to increase performance as the Pi runs incredibly slow during certain tasks, namely, streaming videos from Youtube.

It barely plays them, stuttering constantly making them unwatchable.

Is there any suggestions on why this low performance could be occurring? I was hoping it would be related to the low power warnings.

[lumsdot]

glad it works

im using chromium as my browser on my pi3

viewtopic.php?t=121195

it by far the best and fastest browser for the pi

youtube works in the browser at 320p and works outside browser as well
read instructions on first page on how to install and the youtube options

i find chromium browser to be faster on my pi, than using my windows 8 pc to browse the internet

you could try overclocking as well, 13000 or 14000 mhz should be possible