hi....i am doing one led cube 3x3 project with PIC 16f877a. I want to raise the brightness from OFF to full brightness gradually.is there any hardware set up for this....

 

Depends, do you want it to cycle, or do it once? You can also go with a PWM method, or analog using transistors and an RC circuit.

Here is a circuit out of my LEDs, 555s, Flashers, and Light Chasers article, chapter 5.

PWM as the advantage of being able to go the absolote lowest power supply voltages. The analog method looks something like this...

You can replace R4-R6 on the first schematic for R1 and C1 on the second to make the first a fader.

If you want a throbbing LED then this will work...

Q1 and Q2 on both circuit must be separate transistors, you can not use a packaged darlington such as a TIP101 or TIP102. The exact transistor part numbers are not critical other than that.

 

Actually, you can do all of that using PWM and Charlieplexing to control the 27 LEDs.

You'll have to use resistors to limit the maximum LED current.

Google is your friend.

 

thanx lot friend...let me try out this....i think this will workout..