2 LEDs and one pin left

[ScaleRobotics]

However, the bad news is that Sayzer is right. You can't get three states "0,0", "0,1", and "1,0" with only one MCU pin.

Really? Because I am using Dave's code on a 18F26J50 (3.3 volt) with no resistors, and it works like a charm. Red, Blue, off

BLINK:  
     HIGH PORTA.0 
     PAUSE 250 
     LOW PORTA.0  
     PAUSE 250   
     TRISA.0 = 1 
     PAUSE 2000    
     GOTO BLINK

[rsocor01]

Really? Because I am using Dave's code on a 18F26J50 (3.3 volt) with no resistors, and it works like a charm. Red, Blue, off

BLINK:  
     HIGH PORTA.0 
     PAUSE 2500 
     LOW PORTA.0  
     PAUSE 2500   
     TRISA.0 = 1 
     PAUSE 20000    
     GOTO BLINK

DOH,

The trick is in the TRISA.0 = 1 to get both off (the 0,0 state). Nice!

Robert

[Darrel Taylor]

I think this page explains what Walter is doing pretty well ...
http://www.batsocks.co.uk/readme/p_tut_led16.htm

[falingtrea]

Simplest coding would be to generate a square wave signal on the pin, and then set the TRIS based on state of each LED. TRIS would have to be set every time you change the state of the pin in the square wave generating code. That way the LEDs will always be the same brightness. Of course the square wave signal would have to be interrupt driven off of a timer in order to have both LEDs on at the same time.

[sayzer]

Really? Because I am using Dave's code on a 18F26J50 (3.3 volt) with no resistors, and it works like a charm. Red, Blue, off
Attachment 4604

BLINK:  
     HIGH PORTA.0 
     PAUSE 250 
     LOW PORTA.0  
     PAUSE 250   
     TRISA.0 = 1 
     PAUSE 2000    
     GOTO BLINK

Nice trick indeed.
How about RED and BLUE = ON ?

(without ".....Of course the square wave signal would have to be interrupt driven off of a timer in order to have both LEDs on at the same time. " )

[ScaleRobotics]

Nice trick indeed.
How about RED and BLUE = ON ?

(without ".....Of course the square wave signal would have to be interrupt driven off of a timer in order to have both LEDs on at the same time. " )

Nice one Sayzer! I guess that is four states for one pin!

[rsocor01]

Nice one Sayzer! I guess that is four states for one pin!

Yes, the four states can be obtaind with only one pin. Very nice!

Now, if you use the red-green LED that I mentioned above a cool project can be made.

http://futurlec.com/LED/LED3RG.shtml

Since red + green = yellow, then with only one pin in the MCU we can obtain four different states in the LED: off, red, green, or yellow. Also, by varying the percentage duty cycle of the square wave different shades of yellow can be obtained. I haven't tried this yet but it might be a cool project.

Robert

[sayzer]

RED and BLUE = ON

The only way I can think of is to connect them in parallel. (if serial, 3.3V will not go through)

[rsocor01]

RED and BLUE = ON

The only way I can think of is to connect them in parallel. (if serial, 3.3V will not go through)

No, that's not what I meant.

If you apply a square wave to this red-green LED, the colors will change so quickly that it will look like it is yellow. I haven't tried it yet, but I'm pretty sure it will look yellow to your eyes.

Robert

[mackrackit]

Hey Robert,
Can you give some example code for how the square wave method would work?
Say you have something like the sliding door app.
Green = full open
Red = closed
OFF = inbetween
Yellow = moving