Hi finansh,

I'll give you the next couple of jigsaw pieces...

You asked how to get all the dots lit. Short answer is: you don't! Instead, you light one entire row (or one entire column, its up to you). After a short pause, you then you move to the next row and so on until each row has been individually lit for the same short time. Then repeat. Do this fast enough, perhaps 50 times per second, and it will appear to the human eye that all the dots are lit. This technique is called multiplexing.

Resistor values: you need just a couple of figures from that confusing data sheet, and a formula called Ohm's Law. R = V / I where R is the resistor value, V is the voltage across it and I is the current flowing through it. We will use the law on the resistor, not the diodes in the matrix.

The important figures from the data sheet are the Forward Voltage (Vf) and typical current (I typ) of the dots. The Vf is 4.0V. This is a surprisingly high figure, until you realise that each dot in this particular matrix has two LEDs, and may present some challenges later. The typical current is 20mA (maximum continuous is 30mA, but 20 will do for now).

So the dots need 4V to run, but your power supply is 5V. We need to get rid of 1 Volt, and this is what the resistor does for us. The same current will flow through both the resistor and the dot. The dot will use 4V and we want the remaining 1V to be used ("dropped") by the resistor. So, using Ohm's law, what should the resistor's value be?

Paul