Sequential LED flasher modification

[cheapNdisgusting]

I'm not an expert, but rather an experimentor. I built a 10 led sequential flasher (only one lit at a time) and works great. I used a 555 for the clock and a 4017 CMOS IC. What I want to do is use bi-colored LEDs and use another 555 and 4017 to make (at my discretion with a switch) change from red to green, using the same LEDs. <p>If I try this, it will either work or smoke. Or am I going at it the wrong way. Is this a place for a different chip?<p>I didn't try it yet and would appreciate any advice. Thanks in advance.

[Mike6158]

Just a thought (same here by the way... experimenter), could you use the output of the 555 to trigger a MOSFET that sinks the cathode to ground then use a switch to toggle the power to the respective anode? I'm assuming that the LED's are common cathode and not common anode. If they are commone anode you could forget the MOSFET and switch the individual cathodes to ground.
<EDIT>
Hmmm... my bad... I didn't pay attention to what you are doing. I was thinking series not sequential. You could adapt the idea to transistors though...<p>[ February 17, 2005: Message edited by: NE5U ]</p>

[philba]

How do your bi-color LEDs work? 3 leads with a common cathode is pretty typical. You could do what you suggested but then the two counters/oscillators would be out of sequence. Better to drive both counters from a single timer. From what you said, I think you want to be able to switch from one color to the other rather than both being lit and not lose position (eg when #3 is red you flip a switch and #3 goes to green). Is this correct? <p>Basically you need to have at least 3 states - both off, green on/red off, red on/green on. You could add a fourth - both on. I'd use octal tri-state buffers (74hc541). 2 for red and 2 for green (you waste 6 buffers but they are cheap). Use the tristate lines to inhibit the one you dont want lit. The nice aspect of this is that you can drive both sides from a single decade counter. You will definitely want HC logic for its drive capability. Tristate the red side to light green, green to light red.<p>You could also do this with driver transistors configured as emitter followers for each LED. Bases go to the decade counter outputs. Switch the Vcc on for the LEDs you want lit. I like this solution a little better but its a lot more parts and soldering. Also, you can drive the LEDs a lot brighter with this approach.

[cheapNdisgusting]

NE5U and Philba: Thanks for all the advice.
As to what type of LEDs I have ~ a little of this and a whole lot of what my wife refers to as (you get the idea) I will buy all identical LEDs for the final "no more smoke project". I have some of the 3 lead ones and more of the 2 lead ones. 2 lead ones are easier to get also so that will be my first choice. Also, where the pattern starts and stops/switches to the other color is not important as there will be a small delay between the two cycles. Actually the colors will identify "fast" and "caution" on the finished project.<p>I will spend some time now putting this together and will let this thread know how it comes out.<p>Again, thanks.

[dacflyer]

i did this in sort of a way long ago with a 556 times..and a 2 lead bi-color led..
the output was random...either you got a red or green or nothing..
1 lead was connected to each output of the 556
and same parts for the timing was used..but they were slightly off..so that what gave the randomness..was kinda neet..but doing this with 10 bi-color leds will be more neeto

[cheapNdisgusting]

Upon reading a little deeper, I've decided to go with 3 lead LEDs.<p>Again ~ thanks.

[cheapNdisgusting]

WORKS GREAT!!
Using the 3 pin LEDs, a 556 as an astable multivibrator, and two 4017s, and using two different sets of capacitors and resistors for the timing seq. I now have a green sequence that repeats about every 3/4 second and a red sequence that repeats about every 2 seconds, at the discretion of my switch position. Perfect for my project that displays a fast or slow speed.<p>Thanks again for the help.

[dacflyer]

great...i got a ton of 2 lead bi-color leds i still have to find a cool use for.. :p