Make An Illuminated Scrolling LED Dot Matrix Sign for Your Layout

It's really easy and relatively inexpensive to make the scrolling Dot matrix LED sign I used in my last layout. 



You need 3 things: 1.) An LED display; 2.) A brain to control it; and 3.) A power source.

1.) LED Display
You could use a single 8x8 LED matrix but this is a bit limited and not ideal for scrolling a message, so I used what's called a 4-in-1. It's essentially 4 of these 8x8 displays joined together on a single PCB. Each of the 4 8x8 displays is controlled by a MAX7219 IC. You don't need to worry about that as it all comes pre-built as a single unit. 

So the full name to search for online is something like '4-in-1 MAX7219 Dot Matrix Display Module'. They are sometimes advertised as Arduino parts.

You can find them in red, blue or green varieties. Red seems to be a buck or two cheaper. As an added bonus they usually come with the required hook up wires as seen here:



Here's one on Ali-Express for about US$2.50:
https://www.aliexpress.com/item/33016361...4c4dJ4pz2r

2.) The Brain
Next you need a brain to control the display and send it the message.

A lot of people use the popular Arduino for this sort of thing and I did read of people using Arduino Uno boards. I don't have one of those so can't really advise on it.

Personally I used a BBC Micro:bit board. Why? Because my son had one he used for school and I knew it was simple, small and inexpensive. Something like a Raspberry Pi would work also but it's way overpowered and overkill for a simple task like this.



You can find a BBC Micro:bit controller on Amazon for about US$18 here:
https://www.amazon.com/BBC-micro-micro-c...01G8WUGWU/

Now if you are up for the challenge and want to save a few bucks you can solder (or clip) onto those IO pins on the board itself. I recommend though you get an expansion board with raised pins that lets you easily plug and play. The Micro:bit plugs into this expansion board and allows you to connect the wires directly to the 4-in-1.

The way you want to connect them is:

Code:

Micro:bit -> 4-in-1 Display
GND  -> GND
3.3V -> VCC
P13  -> CLK
P15  -> DIN
P16  -> CS

There are only 5 wires to hook up so it's easy peasy. This is what mine looks like after plugging in the wires to the expansion board:



Here's an expansion board on Amazon for about US$4.60
https://www.amazon.com/Moligh-doll-Expan...07TXBXJ4X/

The last thing you need for your brain is software to control and send your message to the display.

The MakeCode editor which is an online web based code editor for your Micro:Bit allows you to search for public extensions. Search for one called MAX7219. This extension knows how to control the MAX7219 chip on your display. It's designed for kids so it's really simple to use in the editor with drag and drop. Read more instructions on how to use the software extension here:
https://github.com/alankrantas/pxt-MAX7219_8x8

3.) Power
Most 5V phone charging USB power sources should be fine to run the Micro:Bit with a 4-in-1 connected. If you try to run more than a single 4-in-1 display (you can chain them together you know) you may need an additional power source hooked up straight in to the displays. You will see some pins on the back of the 4-in-1 that enable you to connect to external power if required.

I use a small powerbank phone battery to power my microbit. The single 4-in-1 display gets it's power straight from the Micro:bit itself and is quite bright without any external power.

I use a small battery I already had lying around which was too small and useless for modern phone charging anyway. It's similar to this one on AliExpress for $US5 bucks and it's more than adequate:
https://www.aliexpress.com/item/32902062798.html

Of course you could also plug straight into a 5V USB wall charger too. As long as you can get at least 1A (1000mA) output you should be fine.

Total Cost and Parts Summary
Total outlay if you had to purchase everything from scratch:

$02.50 - 1 x 4-in-1 Dot Matrix Display
$18.00 - 1 x BBC Micro:bit controller
$04.60 - 1 x Micro:bit Expansion Board
$05.20 - 1 x 3000mAh Power Bank

$30.30 - Total (not including shipping)

[Super]

Thanks Finno, very interesting. Wish there was ones that came all together is a kit/set. Does the controller stay plugged in at all times or can you program the lights and unplug the controller to program other lights? Or maybe I have this all wrong and the controller and programmer are 2 different things.

To put a new program on the Micro:Bit you juts plug it in to your computer via USB, got to the MakeCode webpage, update the program (ie. change the text you want to display), and then transfer that to the Micro:Bit.

Then unplug and put it back in your layout.

I could even make the program for you saying whatever you want, send it to you as a small file and you transfer it on to the Micro:Bit, just like dropping a file onto a USB drive.

[Super]

Is only programed for scrolling text or can it do other things too?

The program I use has pre-built routines to display either scrolling text, static text, blinking text or if you are feeling arty you can turn each individual LED on or off to create smiley faces, symbols etc.

[Super]

Thats what I was hoping for. Can you also use in in combination, for example the Text Scrolls in, goes static, then starts flashing before continuing on to the left?

Thats what I was hoping for. Can you also use in in combination, for example the Text Scrolls in, goes static, then starts flashing before continuing on to the left?

I think so. This is what it looks like in the MakeCode editor. It is a really simple, visual environment for programming the Micro:bit.

Here is my original program you see with the MegaCity 3 text programmed to scroll. There is some setup stuff on the left and the forever stuff is where the message is coded so it just loops forever.



Now lets add some more steps. we can select the 'Display text' routine and drag that in to our forever loop for some static text display.



Finally we add in a little pause and change the brightness of the LED's so it creates a blinking effect.



Last thing to do is save the program on to your computer as a small file. Then transfer it to your Micro:Bit using USB just like a thumb drive.

This is just a very basic example but if you play around there is much more you can do including setting all the individual LED's separately. 

If anyone ends up getting all the parts and you get stuck I am happy to walk you through exactly what you need to do.

[Super]

Thanks Finno

I do always get a good chuckle when someone says "really simple"