20 x 4 RGB display with RasPi.

Components & Accessories Displays
1

I am really hoping I haven’t shot myself in the foot buying this display.

I have (past tense) built an Arduino clock with a different 20 x 4 display.

But now I am playing with RasPies.

I had to hunt around to find a 3.3v display and saw this one with RGB backlighting.

So I bought it. It has I2C and SPI ports. Too easy!

Because I am playing with a RasPi, I am also using node-red.

I saw there is a node that has the specs to talk to this kind of display.

Uses the same driver.

But then I found the world of hurt.

The node is written for I2C addresses 2x and 3x. Not 72 that this display was saying to me on the RasPi.

I am wanting a display to which I can send data (or more so: text) and have it display.

But it would seem that only via FTDI can I use it as a simple display.

Yes, this has an AVR in/on it.

If I have to upload a program to the display’s AVR, fair enough I guess. But does such a beast exist allowing me to do what I want?

What do I need to do to get it so I can send it messages like:

“Hello world” and that be displayed?

Other message structures would be slightly more complex in that:

“Hello world@x,y” would print it at the x/y position on the screen.

x - 1 to 20

y - 1 to 4

Getting more fancy: I would like control of the back light, cursor, position, the cursor blinking (or not) and programmable characters displayed.

All controlled form a RasPi running Node-Red.

I don’t know if I could use the FTDI port to talk to the display directly as shown in one of the clips. Is that basically just a couple of pins on the RasPi’s GPIO pings?

Help appreciated.

2

You might start with serial as that’s going to be easier to code for than I2C or SPI. All three will work and you send the same data for all three but there’s less overhead as far as programming goes for serial.

Also, check out the hookup guide for details on commands and how to use them. You will probably want to download the Arduino library and look at what the code is doing. (Testing on an Arduino is recommended) The hookup guide can be viewed at the link below.

https://learn.sparkfun.com/tutorials/av … -guide/all

3

Things have moved on from there a long way.

After downloading and installing (both) versions of the python qwiic drivers, the display works.

Both versions: As in python2.7 and 3.7.

Actually finding them was a journey down the rabbit hole and though I did find out some interesting things: why isn’t there a direct link to the ultimate software package on the page with the display?

(And why don’t you keep your distributors up to date with this also?)

I didn’t know the RasPi had a native serial port on it. Which pins are they?

The big (Huge actually)problem is that when I send a command to adjust the back light, the display cycles through a somewhat larger number of colours than simply changing to the colour I sent.

The attached .zip file is a video of the display being used.

Alas it is using the python2.7 code, but even after updating to 3.7, the problem remains.

How about you look at the video and see if you can see the problem. It is only about 6 seconds long.

Because I think that irrespective of how I talk to the display, that is going to happen.

LCD.zip (3.7 MB)