OLED versus LCD Display and power consumption.

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HertzHog

Member
When selecting a serial display to buy for a battery powered project, power consumption is crucial. I have read the specs of the OLED displays in the shop and the description clearly states in several places they draw less power than LCDs making them more efficient than LCD! I can't imagine how that can be true. Do they mean less than a comprable LED display? I thought LCD were very power frugal and could not be beaten on this score.

(Let's assume there is no need for a back light.)
 
A

AllyCat

Senior Member
Hi,

Certainly a "Directly Driven" LCD display (for example as used in a wristwatch) can have extremely low power consumption. But the "serial" displays use a Multiplexed Display Controller (such as the "HD44780") which the data sheet implies requires about 0.5 mA. That's similar to a PICaxe running at 4 MHz, so the best you might expect is a total power consumption of 1 mA, with no backlight (or negligible current in the OLED elements).

It rather depends if you consider 1 mA to be "low power" consumption. It is, compared with a "normal" LED backlight, or many other components such as a radio receiver, relay, voltage regulator ("7805", etc) or even poorly conceived switches or drivers, etc.. But it might be excessive for "24/7" operation from a small battery (AAA or AA, etc.).

One of my present "projects" is using a PICaxe to drive one of the "I2C expander backpacks" on a backlit LCD display and I've just measured the "power budget" as follows: The PICaxe (08M2) draws about 1 mA (because it's running at 16 MHz) and the total battery drain rises to ~5 mA when the LCD module is connected. That's more than I would have expected; I think much might be due to the red "pilot light" on the back of the I2C backpack which performs NO functional purpose! The (green) backlight is controlled by PWM and the "dimmest" settings (still adequate in indoor room lighting) add almost nothing to the current consumed (~ 100 uA).

In summary, I suggest that for a "low" current application, there may be other factors than the difference between LCD and OLED technology. However, it may be (much) easier to lower the LCD backlight current (e.g. by not connecting it! ) than an OLED. But I don't currently have a hardware setup to do a "side-by-side" comparison. The other significant factor is that a backlight consumes the same current whether any of the LCD pixels are "lit" or not, whilst the OLED current rises when more pixels are (actually) lit.

Cheers, Alan.
 
D

Dippy

Moderator
I've never seen wrist-watch levels of current consumption with the cheapo 'General Purpose' LCD character modules you get.
I would guess that all the cheapies are using old fashioned drivers that are cheap.
Perhaps there are some special/newer versions?

I see that LCD drivers from NXP and ROHM are in the microAmp range so maybe some display manufacturers has adopted them (or similar).
You'll have to hunt around. Or roll your own display which would be fun.

I have seen very low current available on Graphic OLED modules using the Solomon drivers in Sleep mode.
Needless to say, flat out with all dots on they are going to take some power.

And there are some very low power graphics LCD modules around (microwatts) ; Sharp for example.

But I have yet to see very low power character LCDs at tight-fist prices.
Perhaps they are lurking in a dusty, dodgy corner of Fleabay.... ;)

Unless some kind soul can find something you may have to power off/on/restart.
 
H

HertzHog

Member
The question was very simple. Ignoring a LCD back light, would a Picaxe shop bought very similarly driven 2 line serial display really use less power if it was the OLED version (as the description implies) or one of the LCD versions. As I am struggling to belive the claims from what I have read here. I would expect a light emitting technology to use more power than a LCD display but the bumpf says otherwise.
 
Technical

Technical

Technical Support
Staff member
To get anywhere near a comparative viewing distance / brightness you need to compare the OLED with a backlit LCD. Even then the OLED is much more visible.
Therefore OLEDs are normally compared to backlit LCDs, and then the OLED has a much lower current consumption than a backlit LCD. Since introducing OLEDs we have actually removed the backlit options such as AXE033B from the store, we no longer stock them as everyone was buying OLED instead!

However if you want the lowest possible consumption, and are not worried about viewing distance/angle/brightness, then the non-backlit LCD is most current efficient.
 
H

HertzHog

Member
Thanks,
So in the shop description OLED 'lower power' really means lower than it used to be and NOT lower than the otherwise similar LCD displays. That could be misunderstood by many.
As the driving circuits seem so similar, I think the LCD current draw must in use be much lower than the ~45ma the OLEDs have been described as running at when lit up.
I think for my battery powered application LCD will be the way to go. It only needs to refresh infrequently. The display chip seems to use ~ 2ma and then there will be the 18M2 itself.
 
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