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Topic: Question On LED Matrix (Read 286 times) previous topic - next topic

HoboGreed

I am failing to understand how all LEDs are individually addressable for all combinations. For example. if you just wanted to turn on just two LEDs in opposite corners I don't see how as it would also turn on the other two LEDs in opposite corners. (see attached file).

larryd

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larryd

#2
Nov 16, 2018, 06:02 pm Last Edit: Nov 16, 2018, 06:38 pm by larryd
If you make 9  HIGH and 13 LOW this turns on the corner LED.

If you make 5  HIGH and 16 LOW this turns on the other corner LED.

One at a time.




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HoboGreed

So you need to pulse them back and forth individually to make them both appear on at the same time. Wouldn't this make those LEDs appear dimmer ? Thinking treating all combinations should be addressed this way. Saves a lot of power.

larryd

#4
Nov 16, 2018, 07:01 pm Last Edit: Nov 16, 2018, 07:04 pm by larryd
A component like MAX72xx can be used to drive your matrix.
Notice Rset is used to set the LED brightness.

See:
https://playground.arduino.cc/Main/MAX72XXHardware   











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PaulRB

#5
Nov 16, 2018, 07:49 pm Last Edit: Nov 16, 2018, 07:57 pm by PaulRB
So you need to pulse them back and forth individually to make them both appear on at the same time. Wouldn't this make those LEDs appear dimmer ? Thinking treating all combinations should be addressed this way. Saves a lot of power.
Yes, it makes the LEDs dimmer. And this does save power. But the loss of brightness may not be as bad as you might imagine. In an 8x8 matrix, you can light up to 8 LEDs at the same instant, either in the same row of in the same column. Then you cycle through the 8 columns/rows, so each led it lit for 12.5% of the time, which sounds bad. But, for two reasons it is better than you think.

First, when good quality leds are used, they are often rated for a higher pulsed current than their continuous current rating. So because the LEDs are only on for 12.5% of the time, they can be pulsed at perhaps 40mA, which would damage them if it were a continuous current, because the max continuous current is often 20mA.

Secondly, 12.5% brightness looks much brighter than you would think. The human eye becomes much more sensitive at lower levels, so it might look more like 25% as bright.

So combining the two techniques, the LEDs may only look half as bright as if they really were all on at the same time. Modern LEDs are very bright and efficient at turning power/current into light. So the brightness level you get will be good enough except perhaps for use outdoors in bright sunshine. And in bright sunshine, even LEDs at full brightness are often not bright enough!

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