Big LCD Selection

I want to build a big project containing 2 Arduino Mega and 18 sensors for each board. Each board will have its own Sensor Shield. So i will need a lot of lcd displays. 5x2004 displays for each board. Is there a bigger lcd display i can use with i2c connection (or other connection) as the display will be positioned 40cm away from the boards and NOT on them?


Go on. Sit down and think about your project.

A single monochrome GLCD could display different information. e.g. Info in BIG Font for current focus. Small font for other Sensors.
Or a single Colour TFT could display even more.
Anything would be neater and tidier than five 20x4 LCDs.


I dont need graphics, only text. The 20x4 font size is good enough.
I found a 128x64 lcd screen but i dont know how many rows it can display. every code sample i found was about graphics.

128x64 can display 8 rows of 21 characters. 192x64 can show 8 rows of 32 characters.

A 20x4 is similar in size to a 3.5 inch diagonal TFT. i.e. 480x320 full colour pixels.

You would not want to cram large amounts of text into any screen. Whether it is GLCD, OLED, TFT you can use attractive fonts of different sizes. It is not compulsory to use any graphics. Nor do you have to use attractive fonts.

As I suggested earlier, a nice cup of tea can help your design process.

Transreflective LCD and GLCD have very small power requirements. e.g. for battery applications.
Anything that is mains powered does not really care.


The whole project will be placed in an engine room monitoring 2 engines. Sensors will track temps and pressures.
The lcd screens will be placed on a big console with the other engine controls almost 2 meters away from the operator. So I need big fonts so the readings can be easily readable.
Using a 3.5 lcd with many rows means that the letter fonts would be small. Correct?
If I use the 128x64 in graphics mode, how many lines can I have?

If I use the 128x64 in graphics mode, how many lines can I have?

128x64 can display 8 rows of 21 characters (that are similar size and shape to your 4 rows of 20 characters)

The important feature of GLCD is that you can use different size fonts and place text anywhere on the screen.

Which is why I suggested the cup of tea. A biscuit might help.
Draw examples of the information you want to display.

I would want a bigger font if I am viewing at 2000mm distance.

A colour display might show RED or GREEN for important status. A Monochrome display might flash the background or invert the pixels.

You will notice colour from a long distance. In which case you investigate the information. e.g. walk up to the panel.


Hello David.
I dont want to display anything special, just :

Oil Temp 70o
Oil Press 2 bar

and another 15 readings like that per board.
Thats why i said i need only text.


Bringing back this old thread.
I bought a ST7920 lcd display. I managed to connect it and display everything I wanted.
My question is: the diagram says I need to connect 3.3v to the BLA for backlight. I saw some schematics whith connection 5v to BLA or with 5v and a 220 resistor.
Is it possible to connect 5v?


Post a link to what you actually bought.

Yes, of course you can connect BLA to any voltage via a series resistor.

A typical backlight might need 50mA.
If the module is designed for 3.3V on the BLA pin, (5V - 3.3V) / 50mA = 34R

For a 20mA backlight: (5V - 3.3V) / 20mA = 85R

Some modules do not have any resistors on the pcb. So your calculations depend on the Vf of the LED.
A typical White LED might have a Vf = 2.8V @ 20mA

For a 20mA backlight: (5V - 2.8V) / 20mA = 110R
For a 10mA backlight: (5V - 2.8V) / 10mA = 220R

You won't go far wrong by starting with a 220R series resistor. See how it looks.
Experiment with different resistors.

Seriously. Many Ebay ST7920 modules are designed for 5V. You just plug and go.
But there is no harm in being cautious.


p.s. Now do you see why I always ask for a link to your display.
I could have answered in one sentence !!

Thank you David for your time.

This is the link, the IIc module is not suitable for the lcd.
5v 128x64 lcd display from ebay

It doesnt have a backside photo.

Another question.
I use this code line :

U8G2_ST7920_128X64_1_HW_SPI u8g2(U8G2_R0, /* CS=*/ 10, /* reset=*/ 8);

If i use it like this, can i connect another lcd like the above?

U8G2_ST7920_128X64_1_HW_SPI u8g2-1(U8G2_R0, /* CS=*/ 7, /* reset=*/ 6);


Your link shows a ST7920 display and an I2C backpack.

I have never seen anyone use a backpack with a ST7920.
Nor am I aware of any libraries that use a backpack with ST7920.

So I suggest that you just put the backpack in a drawer and forget about it.

Yes, your first constructor should work fine.

No, you can't use two ST7920s on the same SPI bus. Just use two different SW_SPI constructors.

I would be much happier if I could see the pcb.
Does your pcb look like this one from Ebay ?


Yes David, that’s the one.

The IIc provided is not suitable for the lcd but there are backpacks suitable . For now i wont use any, I will have it connected in SPI mode

Well, it is possible to use the 8-bit backpack but it would be very SLOW.
And would require someone to write a suitable library for you.

There is no point in using a 16-bit I2C backpack. It is slower than SPI.
And someone would have to write a library for you.
And yes, I think that I have actually written the library for DIYMORE adapter and tried it.

The display should work fine with 5V.
I am confident that you can connect BLA to 5V because it looks as if R10 is in series.
If in doubt, try an external 100R between 5V and BLA.


Ok thank you David

My two cents about driving LCD backlight, I suppose it uses LED.

You should provide constant current instead of constant voltage, this post about LED backlight explain it.

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