SparkFun Forums

[Guest]

Question: I am attempting to power 8 LED's from individual pins on a single port. Currently the only thing I can get to happen is that three lights can turn on. I am using the Atmega 128 mini Header board, powered with 13.4V. If I program it with a signal to more then three of the pins... then the LED lights merely flash, not a solid 'on'. Are there any suggestions?

Thanks

[Guest]

What is the current consumption of 1 of your led ?

[Guest]

The voltage reg that comes with the 128 is LM78L05 if you google this part it only outputs 100 ma, add the 128 plus all led current consumption and you might be over the limit.

[Guest]

I believe that current consumption is definitely the problem. When calculating it out, there should only be two lights in actuality that turn on... Can you think of a solution to my problem? One possibility I can think of is to use a power source and BJT's to switch each of the lights on using the output pins from the Atmega as an input. Is there a simpler solution for this... perhaps ordering a different voltage regulator, and merely replacing it (not to sure if the header board is designed for that)? [/quote]

[Guest]

Solution: remove the jumper (jp1) of the lm78l05, feed a well regulated 5 volt to the 128 (pins 21,52 +5v) (pins 22,53 gnd). There's lots of voltage regulator that can supply lots of current (PC power supply, old commodore power supply from thrift store/surplus store, surplus store sells lots of well regulated +5v closed and open frame, 7805 in the TO-220 can supply about 1000 ma with the proper heasink, 7805 in the TO-3 can supply even more) it really depends on what is your final product.