Making a bicolor LED blink red/green

[Eddie Klein]

I'm attempting my first electronics project. I have some two lead biclored red and green LEDs. I want them to blink from red to green using a 3v coin cell. With having only two leads I assumed by simply connecting + to + and - to - that I would have a blinking circuit. WRONG...What I have is constant red or constant green depending upon which lead is connected to + or-. I'm sure there is an easy straight forward way to make them blink but I don't know how to do it. Can anyone help please. Thanks

 

[davenn]

What I have is constant red or constant green depending upon which lead is connected to + or-.

That's correct, to light the opposite colour the voltage needs to be reversed.
So to have it blinking back and forwards between colours you would need a
circuit to reverse the voltage

here's a circuit I found, I'm sure you could have found it too ( google is a wonderful thing )



cheers
Dave

 

[KrisBlueNZ]

Hi Eddie and welcome to Electronics Point

Here's another option that will work (barely) from a single 3V battery and will run for a reasonable length of time.



The blink rate is determined by the product of RT and CT. You can vary either one to change the blink rate.

U1 is a CD40106B hex inverter with Schmitt trigger inputs. This may be available from your local electronic components store, otherwise you can get it from Digi-Key (http://www.digikey.com) or Mouser (http://www.mouser.com). It's available in a DIP package (the type with pins that go through the board) or an SMT (surface-mount technology) package that mounts flat onto the board. The DIP package is easier to prototype with, but larger.

CD is a 100 nF or 0.1 µF ceramic capacitor that must be connected

RL affects the brightness of the LEDs, although at 3V that circuit won't deliver very much brightness - try it and see whether it's suitable or not. Reducing RL increases the brightness; you can reduce it all the way to 0Ω (i.e. a short circuit) without harming anything, if the supply voltage is only 3V. That will give you the brightest indication you can get from that design (unless you find a more efficient LED).

You can build the circuit on a breadboard, a piece of stripboard, or using "skeleton wiring".