memory based control to access a grid of LEDs

[aglonen]

I want to design a simple area-efficient control to access a grid of LEDs ( 20 x 20) - 20 rows and 20 columns. If I want to turn ON a particular LED in a grid it should remain ON until I turn it OFF again. Is it possible to turn ON all the LEDS in parallel or turn ON any specific row or column? any design ideas or guidelines are much appreciated. Can I make some sort of flip-flops and/or S-R latch based design and access the grid of LEDS with fewer inputs so that LEDs should remain ON until turned OFF again?

 

[BradtheRad]

Have you considered D or JK flip flops? These can be configured for pulse-ON, pulse-OFF at one input wire.

Now if you were to install the proper resistances (and/or diodes), then you could turn a specific LED on, by combining a pulse on one of 20 vertical wires, with a simultaneous pulse on one of 20 horizontal wires, intersecting at the LED you wish to control.

Other LED's in the same row, or same column, will not be affected because it takes two wires worth of juice to do the job.

To turn an LED off, you do the same thing.

You'll have to keep track whether each LED is on or off.

This is direct drive. You'll need 400 flip flops.

If you use SR latches then you will need 40 control wires horizontal and 40 vertical. So you can apply a pulse to either the S lead or the R lead. It will also require careful adjusting of thresholds of operation via resistors and/or diodes.

This webpage has some comparisons between multiplexing and direct drive.



Some other links:

chebe | Lilypad Project 2: The LED Grid, part 1

Arduino playground - MAX72XXHardware