Doh,

Send it to the list, not just to Lawrence :)

Definitely time to go to bed..


> -----Original Message-----
> From: Ashley Roll [mailto:ash@digitalnemesis.com]
> Sent: Tuesday, 5 February 2002 2:40 AM
> To: 'Lawrence Lile'
> Subject: RE: Re: [PIC]: Driving a dual LED
>
>
> Hi Lawrence,
>
> I found it impossible to reliably light more then one LED at
> once as you will find there are multiple current paths if you
> don't float all the other pins when trying to drive one LED.
> And also like you said, there are some combinations which you
> can't do.
>
> However you don't actually need to light them at the same
> time - just light each one in sequence fast enough and you
> can have all the LEDs on at once as far as the eye is
> concerned. :) Multiplexing is a very useful trick. You can
> even get Yellow out of Bi-colour two leaded LEDs.. :)
>
> I've also used shift registers as well. Very useful. But it
> takes less effort to drive the '138 :) just load a number to
> the port, no messing about shifting bits around to send out..
> But it all comes down to what you need at the time and how
> much it costs.
>
> Another thought I just had (beware - its 2:30AM here, so
> sentience is not guaranteed) was to have the LED setup like:
>
>
>                            ^ V+
>                            |
>                           === Cap
>                 ,-|<-,     |
>  PIC PIN >------+    +-----+
>                 '->|-'     |
>                           === Cap
>                            |
>                            V GND
>
>
> Then you float the pin.. When you want to light one of the
> LEDs you set the pins data register to either high or low and
> rapidly switch the pin between input and output.
>
> I've no idea if this would work, but you should be able to
> draw some power thought the caps and may get enough to light the LED.
>
> Like I said, I haven't thought this through properly, and
> definitely haven't tried it, but it might work? Maybe?
> Perhaps I should just go to bed :)
>
> Cheers,
> Ash.
>
> ---
> Ashley Roll
> Digital Nemesis Pty Ltd
> www.digitalnemesis.com
> Mobile: +61 (0)417 705 718
>
>
>
>
> > -----Original Message-----
> > From: Lawrence Lile [mailto:llile@toastmaster.com]
> > Sent: Tuesday, 5 February 2002 1:37 AM
> > To: pic microcontroller discussion list; ash@DIGITALNEMESIS.COM
> > Subject: Re: Re: [PIC]: Driving a dual LED
> >
> >
> > Thanks, Ashley, this is a really cool trick!
> >
> > I suppose you could light more than one LED with various
> > combinations of 1
> > and 0.  I am supposed to be implementing a light bar, sort of like a
> > progress baar on a download, so I will have to count up.
> > This may not work
> > so well in this case, because I think adjacent LEDs cannot be
> > lit in the
> > same color!
> >
> > You suggested a little port expander, another cheap chip that
> > I have used is
> > an 8-bit serial load parallel out shift register, 74HC164.
> > These can be
> > bought for $US0.15 in quantity, I think.  I need to check the
> > datasheet and
> > see how many LED's thay can handle.
>

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