2 LEDs and one pin left

[Jumper]

Hi All,

I have one red LED and one GREEN led and a few resistors and only ONE pin left on my MCU. It would be nice if there is a way to turn on green or red or have them both off.

Since the pin has 3 states it might be possible but today my brain just can't see how. Current goes in .. one LED is on... Current goes out.. the other one is on. But it is possible to have them both turned off without haveing any leaking current when the pin is in tri-state?

I never plan to have them on at the same time... just both off or one or the other on.

thanks!

[mackrackit]

Output HIGH
Output LOW
Input

Maybe

[Jumper]

and what makes the current not flow thru any of them when the pin is in INPUT?

[mackrackit]

From a data sheet.

Setting a
TRISA bit (= 1) will make the corresponding PORTA pin
an input (i.e., put the corresponding output driver in a
Hi-Impedance mode)

http://en.wikipedia.org/wiki/High_impedance

[sayzer]

1,0
0,1
0,0

LEDs on these states won't be possible by one pin.
Instead, use 4017 with one pin.

I have an example here:
http://www.picbasic.co.uk/forum/showthread.php?t=6548&

[rsocor01]

Jumper,

You can use "one LED" only like the one in the link below. This is pretty much two LEDs put together. It is a red-green 3mm LED.

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

1,0
0,1
0,0

LEDs on these states won't be possible by one pin.
Instead, use 4017 with one pin.

I have an example here:
http://www.picbasic.co.uk/forum/showthread.php?t=6548&

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.

Robert

[ScaleRobotics]

Can't you?

[mackrackit]

My turn to say DOH!!!

No matter how you connect two LEDs without extra hardware there will be feed back between the two.

A couple transistors or sayzer's solution are in order for this one.

[mackrackit]

How many DOHs are allowed in one day???

DUH code

BLINK:  
     HIGH PORTG.4 
     PAUSE 250 
     LOW PORTG.4  
     PAUSE 250   
     TRISG.4 = 1 
     PAUSE 2000    
     GOTO BLINK

And

[Jumper]

Then we have the problem with the idle current.... 2 resistors in serie between Vdd and Vss is going to drain the battery. I like the idea! but the idle current will be almost half of what the LED uses when it is turned on (sssuming 5V Vdd and 2V voltagedrop over the led)

I dont have my lab stuff here.. does anyone think the idle current might be lower in the circuit i have attached.. or will smoke come out :-)

Sure there are many ways to solve the problem by adding more things but I am still hoping this will work...

or it will be DOOH and an other design.

Thank you!

[ScaleRobotics]

Square wave sounds more difficult than Dave's code, and any square wave will light up both LED's on a two led with 1 output scenario. And Jumper just wants one, or none to light at a time.