[GUIDE] 3.5 inch HDMI Display - high energy usage

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[GUIDE] 3.5 inch HDMI Display - high energy usage

Post by salami738 » Fri Sep 29, 2017 12:40 pm

Hi,

i got the 3.5 inch hdmi display Kuman
from: https://www.amazon.de/gp/product/B071JD ... UTF8&psc=1
The backlight is adjustable via a small switch on the side.
On the backside there are the following informations:
"MPI3508 3,5" inch HDMI Display B 480x320 Dots V1.0".
The display has the following pcb outline: 85,6mm width, 60,5mm height.
Display outline: 84,6 mm width, 55,5mm height.
Datasheet for main controller: http://aitendo3.sakura.ne.jp/aitendo_da ... 60.jsp.pdf
Image

I tested it on my labbench power supply and with a UNI-T UT139C multimeter, 5V DC, and got the following results:

WITHOUT Raspberry attached
  • Backlight 002% --> 169mA
    Backlight 030% --> 227mA
    Backlight 050% --> 269mA
    Backlight 080% --> 341mA
    Backlight 100% --> 391mA
WITH Raspberry attached (HDMI connection)
  • Backlight 002% --> 245mA
    Backlight 030% --> 304mA
    Backlight 050% --> 347mA
    Backlight 080% --> 416mA
    Backlight 100% --> 467mA
I think these values are pretty high for a screen i want to use in a battery powered project.

Are there any members who have a similar screen and can measure the power consumption?
Does the composite or DPI displays consume a similar amount of power?
Last edited by salami738 on Sat Dec 23, 2017 11:48 am, edited 2 times in total.

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Re: 3.5 inch HDMI Display - high energy usage

Post by oceanmist66 » Sat Sep 30, 2017 12:20 pm

I can tell you running the rPI zero with a composite BW screen draws 230mA sitting on the desktop, no real processor load. Backlight is whatever was set at the factory, which is fairly bright. My 7in HDMI touchscreen (Waveshare clone) draws 480-490 mA (not including Pi) and that thing has a non adjustable very bright backlight. This does seem a bit excessive at higher brightnesses considering the 7in screen has 4x the surface area and 2.5x the pixels and only draws 25% more power.

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Re: 3.5 inch HDMI Display - high energy usage

Post by YaYa » Sun Oct 01, 2017 2:41 am

The main problem with HDMI displays is in fact the power consumption. I do not have such a screen or the proper tools to precisely measure it, but i’ve read many times that those screens were power hungry :?

If zeroboy or/and veteran gamer were looking here, they should help you answering your questions as they both built using HDMI screens
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Re: 3.5 inch HDMI Display - high energy usage

Post by moosepr » Sun Oct 01, 2017 3:43 am

The biggest issue is the beasty chip on the board that is converting the HDMI signal into one the screen can understand. Composite screens suffer the same issues, although it's a different chip, so will have different power requirements.
Get a small cheep LCD in your project https://www.sudomod.com/forum/viewtopic.php?f=22&t=2312
Wrap it all round a battery https://www.sudomod.com/forum/viewtopic.php?f=13&t=2292
Or use a custom PCB to make it really small https://www.sudomod.com/forum/viewtopic.php?f=13&t=2512
or make it really really really really tiny!! https://www.sudomod.com/forum/viewtopic.php?f=13&t=2919

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Re: 3.5 inch HDMI Display - high energy usage

Post by salami738 » Mon Oct 09, 2017 4:38 am

moosepr wrote:
Sun Oct 01, 2017 3:43 am
The biggest issue is the beasty chip on the board that is converting the HDMI signal into one the screen can understand. Composite screens suffer the same issues, although it's a different chip, so will have different power requirements.
This is correct, the RTH2660 hdmi chip does comsume a lot of power, i cant change that.
BUT: The hdmi chip needs a 3.3 and 1.8V supply and the board uses linear regulators (AMS1117).
These regulators burn the power difference between the supply voltage (5V) and the 3.3 and 1.8V and are therefore very inefficient.

A short test with a lower supply voltage of 4.5 V instead of the 5.0 V i used before showed, that the power consumption decreased by 7%! So if someone has a hdmi display and wants a quick win, this is it.

But i want a much lower power consumption, so after hours of googling, i found out, that the PI Zero has a buildin efficient voltage regulator (PAM2306) - Link: https://www.petervis.com/Raspberry_PI/r ... ights.html which supplies the voltages: 1.8V and 3.3V for the zero. This regulator can supply 1A for both voltages, and 1.8V is supplied between PP5(-) and PP9(+) on the zero.

I will now desolder the inefficient regulator on the display for the 1.8V rail and connect it to the efficient regulator output from the Zero.
I will keep you informed.

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Re: 3.5 inch HDMI Display - high energy usage

Post by salami738 » Wed Dec 06, 2017 1:42 pm

Hi,

maybe someone uses the hdmi screen too and want to squeeze out more runtime on batteries.
You can save about 25% power with this screen if you desolder the two AMS1117 chips.
There is one AMS1117-18 (supplies the 1,8V rail) and one
AMS1117-33 (supplies the 3,3V rail).
The display now uses the following currents on the rails:
1V8: 90mA (0,162W), 3V3: 145mA (0,479W) and 5V0: 170mA (0,850W). This is about 1,5W in sum.

Steps:
1.) desolder the two AMS1117 chips
2.) solder a cable on the middle pin of the pad (PIN 2) on both places
3.) solder the 3V3 cable to PIN1 or PIN17 on the raspberry zero w or PP9 on the raspberry zero
4.) solder the 1V8 cable to the 1V8 marked in my image
Image

Now you use the very efficient regulator of the PI to power the display and you will have a addition runtime of +25% on batteries! Have fun!

TODO:
- Find out why the display uses 0,85W on the 5V0 rail. Cant figure it out. Any help would be greatly appreciated.

greetings from germany

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by YaYa » Wed Dec 06, 2017 1:57 pm

Woow perfect tip. I was reading some articles over the net to do the same optimization but on the Pi, the 1.8V regulator could be improved !!!
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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by salami738 » Thu Dec 07, 2017 12:58 am

YaYa wrote:
Wed Dec 06, 2017 1:57 pm
Woow perfect tip. I was reading some articles over the net to do the same optimization but on the Pi, the 1.8V regulator could be improved !!!
Hi, firstly thank you for reading, commenting and asking questions! You are encouraging me and many others to document things and keeping this forum alive!

Did i understood you correctly, that you think, that the 1.8V regulator on the PI isn't efficient (PAM2306)? Do you have links?
The raspberry foundation used a inefficient regulator on the old models, but they are using a better on the new models.

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by salami738 » Thu Dec 07, 2017 1:08 am

My current conclusion on this display is: Don't use it, if you are a beginner.

Necessary steps I have to execute to use this display (with difficulty):
- EASY: Remove the touchscreen and glas layer (Tutorial: viewtopic.php?f=22&t=2744)
- EASY: Cut the pcb, so it fits inside the gameboy case
- MEDIUM: Cut the outer bounds of the display (Difficult, one error leads to a defective display), so it fits better and can be centered better.

Optional steps to reduce the heavy power usage (with difficulty):
- MEDIUM: Desolder the two SMD voltage regulators AMS1117 and connect the outputs to the efficient switched regulator on the PI (+25% efficiency)
- ONLY SHORTLY TESTED: Power the display with 4V5 on the 5V0 rail (+7% efficiency)
In my case these steps are not optional, because the display+raspberry+arduino+audioAmp draws more than the allowed current of the Banggood power supply (rated max 1A).

Steps I am currently working on:
- Desolder more components to find out, where the 0,850W on the 5V0 rail go and reduce that. The display won't boot with only 1V8 and 3V3 attached.
- Desolder the components used for backlight control and replace them with a mosfet and the arduino as pwm source to make my own backlight control (would be nice to have buttons to increase/decrease the brightness with OSD in emulationstation)
Last edited by salami738 on Thu Dec 07, 2017 2:20 am, edited 4 times in total.

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by YaYa » Thu Dec 07, 2017 1:10 am

Actually i have read many articles but all of them seems to refer to old models. So may be right, the new regulators seems to be efficient enough as i cannot find something usefull for Pi3 or Piz :|
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