Countdown timer led bar... Possible or not ?


So it's my first post here :-) Hope tu fins answers !

I would like to create a visual countdown, created by a led bar (let's say 100 leds aligned) that would switch off regulary the leds when the time is going on...

My idea is to propose a visual bechmark to people that do not know to read the time (childrens, deficient persons etc...). For example, it's always quite hard to make the childrens know how long they have to stey on bed until the night is finished. This kind of countdown could be understandable by everyone to know if the night is in the middle or next to finish.

Ideally, this coutdown could be associated to one clock and could take the "start time" and the "end time" and calculate the time beetween that, then switch off regulary each one of the lights, going from 100 lights on starting time to 0 at end time. 

Any idea about this ?

Its pretty well like my car-barduino, which the latest can drive 64 leds at once. I'm waiting for some real boards to play with.


The most efficient solution for a fixed time would be to use a small 8-pin microcontroller, connected to a string of shift registers, with a start/reset button.

If you need a variable countdown, you could use the 8pin uC and represent the time period on the LED bar, and use a couple of buttons to adjust it, or get a larger controller and add a few buttons and a small display.

If you don't want to use a microcontroller, a 555 timer chip and an array of decade counters would do the same thing, using a potentiometer to adjust the timer.