user38322: Just a basic query;
On my understanding of LED Matrix's, The following would light up 4 LEDs.
But what if I only wanted to light up just 3 of those LEDs? The circuit still needs the same inputs, since power will continue across all columns/rows
Thanks
Tom


user19867: Multiplexing is the answer.

If you want to, as an example, light up only LEDS 1, 3 and 4, you will:

activate line A
activate line X
de-activate line X
de-activate lines A and B (yes, B was not active) 
activate line A and B
activate line Y
de-activate line Y
de-activate lines A and B
start again from top

Do this so that the loop takes less than 10 milliseconds and you are actually refreshing the entire matrix at 100Hz, fast enough to trick the eyes of any human being as if the LEDs 1,3 and 4 are lighted up at the same time: persistence of vision is your friend.

38322: <p>Just a basic query;</p>

<p>On my understanding of LED Matrix's, The following would light up 4 LEDs.</p>

<p>But what if I only wanted to light up just 3 of those LEDs? The circuit still needs the same inputs, since power will continue across all columns/rows</p>

<p>Thanks</p>

<p>Tom</p>

<p><a href="https://i.stack.imgur.com/AVpP3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AVpP3.png" alt="enter image description here"></a></p>
 19867: <p>Multiplexing is the answer.</p>

<p><a href="https://i.stack.imgur.com/wHWwJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wHWwJ.png" alt="enter image description here"></a></p>

<p>If you want to, as an example, light up only LEDS 1, 3 and 4, you will:</p>

<ul>
<li>activate line A</li>
<li>activate line X</li>
<li>de-activate line X</li>
<li>de-activate lines A and B (yes, B was not active) </li>
<li>activate line A and B</li>
<li>activate line Y</li>
<li>de-activate line Y</li>
<li>de-activate lines A and B</li>
<li>start again from top</li>
</ul>

<p>Do this so that the loop takes less than 10 milliseconds and you are actually refreshing the entire matrix at 100Hz, fast enough to trick the eyes of any human being as if the LEDs 1,3 and 4 are lighted up at the same time: <a href="https://en.wikipedia.org/wiki/Persistence_of_vision" rel="nofollow noreferrer"><em>persistence of vision</em></a> is your friend.</p>
