Building the digital clock (LED Multiplexing) - what resistors

Other Hardware LEDs and Multiplexing
1

I would like to Play with LED Multiplexing by Building digital clock

This would work like 4x7 LED batrix which each 7LEDs would make 7 Segment Digit.
I wanted to use leds which would be easy to solder and I came accross LILYPAD LEDs available online

https://pl.aliexpress.com/item/10pcs-lot-LilyPad-Led-Red-White-Orange-Emerald-Green-Blue-Yellow-
Yellow-Green-Light-Module-For/32583987549.html?spm=a2g17.10010108.1000023.2.7d1a624dCGVv2M

I wanted to use BC547 Transistors to Switch individual Digit I want to lit at any Point in time. A mit like diagram in the below link (Figure1)
So planning to have 4 Transistor which would select which Digit I want to lit and then within that Digit light all necesssry leds
Lighting each Digit one by one.

The Chart in this example Shows only resistors used with Transistors. But do I Need any resistors when connecting LEDs. Would that 7x4 Matrix work using VCC powered by VCC port of arduino or do I have to consider external power.
If I Need to use external power (e.g. 5V 2A) does it Change anything in Terms of resistors needed

2

Forgot the link

3

Also in the LED modules there are build in 331 OHM SMD resistors.

4

When a tutorial tells you:-

Today, I am going to taught you how to make LED matrix display

You know the writer does not speak English very well. This often translates into a poor tutorial and this one is a stinker. It is crap, you will learn nothing from it find a new one. Even the basic circuit is wrong, using an NPN transistor in emitter following mode to switch a 5V rail. And the software is incredibly stupid.

Best advice to you is to find a new tutorial.

I had a look round and there are not many good ones using individual LEDs rather than a matrix chip. However this looks not too bad for a beginner:- http://amigojapan.github.io/Arduino-LED-Matrix-Display/ You can always reduce the number of LEDs you use.