I built a 10x7 led display project using PIC 16f84a.It is the extended version or the 5x7 display.

My 10x7 display has 10 columns & 7 rows.Circuit is running well.I added some runing messeeges & some designs in it.

My problem is

* when column scaning the brightness of the leds are good.
* when the row scaning the brightness of the leds going low.
* when the letters displaying continuously the brightness falls.

The PIC output pins can draw only 25mA current. Its not quit enough to drive more leds...

Anybody knows how to prevent this??? I hope to extend this circuit to 20-25 columns to display a whole word...

I have attached the connection of LED's

Attached Images

Led matrix.gif (10.8 KB, 76 views)

 

Add PNP drivers feeding the rows (and invert the logic in the program).

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I Didn't Add PNP Drivers First Bcuz I need to change (invert) my whole program.
My Program is too big about 14 pages so many patterns......So I added NPN Transisters to each ROWS.(feeding 7 NPN Transisters).The circuit works pretty well..But...
In my next LED display having 30 columns.So one Transistor is not enough for each ROW.So I'm Planing to add NPN transistors to each 5 LED's in a ROW.Signal is giving to the base from the PIC through 100 Ohm Resistor.

ThankX