I was tasked with a project from wife, and it has been so long since my college days where I played with circuits, plus they weren't one of my strong points in college, where I'm not sure where to start.
My challenge is my wife is putting together a Christmas gift for my niece and she purchased 25 strands of LED battery operated LED lights. The object is to have one strand of LED lights to come on every day. So on Dec 1, the timer can be turned on, and almost immediately the first strand will light, and then the second day the another strand will come on.
IC1-----IC2 = 4017
T1, T2 = BC547
pin15 capacitor, resistor are 0.22uF and 1M respectively
rest of the resistors are all 4k7
The proposed digital Christmas candle light timer circuit can be implemented by configuring the above two circuits with the help of the following instructions:
The left diagram above forms the 25 LED timer circuit which is supposed to light up in sequence from day#1 when the circuit is switched ON, until the 25he of December when the final 25th LeD lights up, at the rate of 1 LED per day.
The stage is formed by wiring or cascading three IC 4017 ICs. The clock inputs of all the three ICs are rigged with the clock output of the right hand side circuit using IC 4060, whose pin3 output is to be connected with the pin14 of all the IC 4017.
R1, R2 and C1 of IC1 are calculated such that pin3 produces a high clock after a period of exactly 24 hours, once the system is switched ON.
This 24 hour clock pulse is fed to the pin14 of the three 4017 ICs so that a high logic shifts in sequence from pin3 of IC1 each day until the 25th day when the last LED at pin#1 of IC3 lights up.
The circuit is powered using two 9V rechargeable batteries, one being connected directly with the supply pins of the IC stages while the other connected through a 1K resistor.
The battery which is connected through a 1K resistor is permanently connected with the circuit and makes sure that the ICs are always powered with the minimum required current, in order to sustain the memory of the ICs in case the main battery gets exhausted in the course of the 25 day period and while the user removes it for recharging and replacing it back.