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Topic: Multiplexer question (Read 715 times) previous topic - next topic

theneh

Hi,

I've just got a Arduino duemilanove and I'm trying to play with 4 multi coloured LEDs. For some reason pins 0 and 1, the rx and tx ones? don't like the LEDs they just flash and pin 13 is quite uncooperative with fading them. So I'm limited to three LEDs (9 pins, 2 - 12). So I'm guessing I need to get a multiplexer. My local store where I got the duemilnove from has these ones:

4051, 4052, 4053, 74HC157, 74LS138, 74LS139, 74LS151, 74LS153, 74LS155, 74LS157

i am wondering which one, if none, to buy since i was reading an article which says the 4051 can't deal with brightness? just on-off...

thanks

Grumpy_Mike

#1
May 19, 2009, 04:22 pm Last Edit: May 19, 2009, 04:23 pm by Grumpy_Mike Reason: 1
Quote
For some reason pins 0 and 1, the rx and tx ones? don't like the LEDs they just flash


They are used as you say for TX and RX so they can't be used for LEDs and communicating with the computer at the same time. You have to override them in software so best not to bother.

Quote
and pin 13 is quite uncooperative with fading them.


Not all pins will output PWM and so not all can be used in fading.

Quote
says the 4051 can't deal with brightness?

It's the only one of that list that does deal with analogue signals, all the other are on and off only, which is what you need if you are using PWM to fade the LEDs.

Please read the the articles on the playground on multiplexing and PWM.

James C4S

TI's TLC5940 allows you to control 16 channels with PWM.  There's a library in the playground that makes the chip nearly plug and play.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

theneh

thanks for the quick reply mike. i went to the local store and bought a 4051 it was totally useless. i've ordered a TI TL5940. the local store guy told me they do free samples i was amazed, free fed ex shipping too. now i just have to wait a week and in the mean time do more arduino tutorials...

thanks again

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