I plan to build a small timer device that, when triggered, lights up 3 leds. After 30 min, the first goes dark, after another 30 min the second and yet another 30 min later the third.
It's pretty easy to accomplish building three separate monostable NE555 stages that share one trigger button. Yet, only one at a time prevents its being retriggered during its high-level pulse at it's output. Question is: is there an easy way to keep all of the 555s from being triggered while any of them is still activated?
I thought of putting a diode between their outputs and the other's trigger input and putting a resistor between the button and ground, so that an active ouput would pull the other trigger inputs high, stronger than the button to ground would pull them down, and due to the diode prevent them from being pulled down if all outputs showed low-level...
Could something like that work? Something like a only-pull-up-not-down mechanism... Any suggestions appreciated. Thanks!