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LED Matrix

I have a LED matrix and I want to light up the LEDs at (C1, R1) and (C4, R4). So I connected R1 and R4 to 5V and connected C1 and C4 to ground.

But the problem is that (C1, R4) also lights up. Is there any way to avoid this?

I have limited number of 5V and ground ports so I can't connect each LED to it's own 5V and ground port. It is also required that (C1, R1) and (C4, R4) are continuously lighted up. So I cannot remove the voltage supply at any instance.

Confuse
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  • Doesn't R1 C4 light up as well? – RoyC Sep 03 '17 at 07:35
  • Yes it does. I just removed it for simplicity. – Confuse Sep 03 '17 at 07:46
  • I understand your motive but please don't do that you cause confusion instead. – RoyC Sep 03 '17 at 08:01
  • It probably cant be done with this scheme [this question](https://electronics.stackexchange.com/questions/11046/how-can-i-control-many-leds-with-just-a-few-pins-on-my-micro) contains some good suggestions. – RoyC Sep 03 '17 at 08:09
  • Since you seem to want to light up any specific number of LEDs and do so continuously and not multiplexed, please tell me how you might use your columns and rows to light up 15 of those LEDs? You only have 12 lines shown. I'm curious how you imagine arranging to light up an arbitrary number of the LEDs in any arrangement. (You can light up several. But only if they lay on a shared row or shared column.) – jonk Sep 03 '17 at 09:19

2 Answers2

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I would have expected (C4, R1) to light as well.

You need multiplexing to solve this problem. Only light one row (or one column) at a time. Switch rapidly through the rows (or columns) to make it appear that they are all on at the same time.

If the display appears too dim, adjust the resistors down a bit. You can get away with this if the individual LEDs are only on for a few milliseconds at a time.

Simon B
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  • Sorry but this isn't viable. I mentioned in the question that the LEDs must be continuously lighted up as I cannot remove the voltage supply at any time. This may sound whimsical but my apparatus is a bit complex and doesn't permit continuous flickering. – Confuse Sep 03 '17 at 07:49
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    Matrix displays **have to be multiplexed** if you want control of individual LEDs or pixels. This is kind of obvious from the schematic. – Transistor Sep 03 '17 at 09:10
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    @YasharyanGaikwad - Sorry to hear that "this isn't viable". I regret to inform you that the universe does not care what you want. With the matrix you have shown, there is no way to do what you want. – WhatRoughBeast Sep 03 '17 at 13:43
  • @WhatRoughBeast Universe is so mean. I was only asking for altering a couple laws after all. – Confuse Sep 03 '17 at 14:29
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What you are asking simply cannot be done, if you truly need continuous lighting. Replace the matrix with individual LEDs, each with its own driver (35 drivers in the above case).

That's a huge increase in cost and complexity, which is why practically everyone uses multiplexing. Simply multiplex faster than the eye can see (1kHz or so is usually good enough; after all, TV displays are effectively scanned at 50 or 60Hz.)