AVR-Chat

If you already have a 2 volt supply capable of 20ma try this


                                         
           About 470ohms. Adjust so green and red are equal brightness   
                       /------\/\/\/------ +5v or Ov            
---+       LEDs       /             
     |     +-->|---+ /              
     |pin  |       |/     47ohms   
     +-----+       +-----\/\/\------- +2 volt supply
     |     |       |               
     |     +--|<---+               
---+                               
                                   
To program:
None= prog pin as input or tristate with no pullup resistor.
One color(Eg. Red) =Prog pin as output and high
Other color (Eg. Green) =Prog pin as output and low                  
                
                                 


 

--- In AVR-Chat@yahoogroups.com, Russell Shaw <rjshaw@...> wrote:
>
> Peter Gargano wrote:
> > I can't figure this out simply. I'm sure there is a simple solution 
> > tho'. Chip is the Mega-168 that I want to add an extra function to.
> > 
> > Assume I have either a two or three pin bi-colour LED (ie. either
back 
> > to back LEDs with two pins, or two LEDs with a common pin).
> > 
> > I have a single pin on an AVR processor that can either be LOW, HIGH, 
> > or Tri-state.
> > 
> > I want to drive the LEDs either both OFF, one on, or the other on,
but 
> > NOT both on.
> > 
> > SO, I have three states the pin can be in, and three states for the 
> > LED to be in.
> > 
> > I can't figure out a simple circuit to drive the LEDs with just one 
> > processor pin. Does anyone have any ideas how to do it using no more 
> > than two transistors? I'm using Vcc=5 Volts and I have a free 2 Volt 
> > (low current) reference point I can use.
> > 
> > I'd be most appreciative of a solution. BTW, the solution cannot use 
> > PWM or anything processor intensive. The spare pin is either and ADC 
> > input or an I/O pin.
> > 
> > Alternative solution: can anyone suggest how I can use the RESET pin 
> > as an output and still retain ISP capability (this is a QFP part that 
> > is programmed after assembly).
>                                         +5VCC
>                                   --+----------+--
>                                     |          |
> AVR                                |c   NPN   >
> ---+       LEDs                     \|b__     < 10k
>     |     +-->|---+                  /|   |    >
>     |pin  |       |     220ohms     |e    |    |
>     +-----+       +-----\/\/\-------+     +----+
>     |     |       |                 |e    |    |
>     |     +--|<---+                  \|b__|    >
> ---+                                /|        < 10k
>                                     |c   PNP   >
>                                     |          |
>                                 ----+----------+---- GND
>