2 LEDs on only one output


So, this challenge is for anyone!
From analog guys to digital guys.
Only thing you should make is get leds turn on and off alternately, when you switch on and off the power.
You can do it from MCu or from power source with button.

Output off.
Led 1 turns off. Led 2 turns on.
Output on.
Led 1 turns on. Led 2 turns off.

1. It's your solution! Use ready IC's or your own circuits.
2. Only one MCu pin or button.
3. You can make it to breadboard, or make a PCB.
4. Make a video which shows your circuit in action, and how is it connected.
5. No mechanical switches allowed on solution!

Here's some pics:


Analog solution


Digital solution

So nice time to solve this challenge!

A simple inverter would do

A simple inverter would do the trick.

Something like a 7404 IC. 


easy metod

you can connect the anode of one led to the pin and the catode of the other to the pin. then you connect one led to gnd and other to vcc… when the pin is high, the one connected to gnd will light up, and when the pin is low, the one connected to vcc will light up too. simple!

i can post one image tomorrow!

That’s the one I’d go for.

That’s the one I’d go for.

That would be ideal for 2 LED control and if you turn the pin into an input you could turn them both off . . . nearly.  You’ll get both on dimly if LED1 Vf + LED2 Vf < 5V , but the problem didn’t specify they had both to turn off so that’s fine. (An extra diode or 2 would probably sort it.)

Nothing, just a fun test.
Nothing, just a fun test.

everywhere on the internet…


set the pin as input to turn on both leds. I have a simple circuit somewhere here to do this with a 3 leg duo-led. a red/green one then can also be orange. I search for it if anyone is intressted.

oh and this one is for 3 leds on 1 pin. (not tested myself):

I’d Connect the output to

I’d Connect the output to both inputs of an AND gate. This would output to both LED’s but one would be via an inverter. Simples

That was stupid, forget the

That was stupid, forget the AND gate -.- just the inverter, its already been said I apologise!

My solution

Actually my version is intended to be used with a bi-color led and controlled by a micro-controller.

I used a simple push button just to test the idea with the transistors.

To see a small video with the device in action follow this link http://www.youtube.com/embed/bbTQ278JIqg?rel=0


Maybe I dont quite get the problem

Maybe I dont understand the full Idea of the contest, but couldnt you just use a relay…

Its too simple.

set pin 9 of arduino to blink and use one NPN and one PNP as shown 



I was coming to this site because I exactly searched for a solution for myself. I found an easy one just with one single Chip LH1512, double solid state relay with NO and NC. I needed a total separation between the power to the leds and the input because the control pin is triggered by a digital signal from other power source.