Ok, I have a small circuit for Digital Electronics class and nobody can seem to get it work in any of the circuits. We have available a circuit board, transistors, resistors, 4 LEDs and two 555 timers. Our teacher says that we have to make a circuit that will have 4 LEDs flashing in sequence so that one is on at a time and the other three are off. I have figured out how to get each 555 timer to work independently and all the values for the resistors and transistors. I have also figured out how to get one 555 timer to run two LEDs opposite each other and one 555 timer to run the other one, but I can not figure out how to fire off 4 LEDs in sequence continuously. If anybody can help me out with this problem I would greatly appreciate it. Thanks!

 

here is one solution:

Attached Images

LED_BLINKER.jpg (21.1 KB, 269 views)

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This link has some more 555 blinker circuits, may help with ideas:
http://home.cogeco.ca/~rpaisley4/xLEDblinker.html

 

There is a small problem with the circuit in the link above: the 555 output does not go high enuf to turn off the PNP. A resistor from base to emitter is needed.

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