555 timer help

I am trying to figure out how to do a "drag racing chistmas tree" using a 555 timer. I want it to start on red until a switch is flipped then go yellow yellow yellow green. With a 1/2 second delay between each light. Could anyone give me tips?

Posted by Jason (jasonlg3d@cox.net) on 28/11/2004, at 20:43 GMT

Use the 555 to drive a 4017 1-of-10 counter

You could connect a 555 astable with a time period of 0.5s to a 4017 1-of-10 decade counter. This can (just) supply enough current to light one LED on each output. You will need to sort out the details, including resetting to zero when you switch on and stopping at green (eg use the disable count input). Try on breadboard first of course!

For 4017 pin connections see: www.kpsec.freeuk.com/components/cmos.htm#4017

For an example project using a 555 and 4017 see:
www.kpsec.freeuk.com/projects/heart.htm

Another idea: if you want to use just 555s you could connect a chain of 555 monostables together, each one lighting an LED and triggering the next monostable when it switches off. Each output will need to be connected to the trigger of the next 555 with a capacitor, you can see an example of this between the left and middle 555s in the circuit diagram for this project: www.kpsec.freeuk.com/projects/levelc.htm

Posted by John Hewes on 29/11/2004, at 14:06 GMT