how to save some power to gradually shutdown a system?

Projects General Guidance
1

hello,

I will remplace an old light by an arduino controlled LED tape (12V @ about 1.5 or 2A max), directly connected to the main power with a AC/DC adapter. So when I push the switch on the wall, the AC/DC adapter is alimented and the LED goes ON, when I push again the switch, the power is cut and the light goes off. No problem for this.

BUT, I want to do the following: make the light going off gradually (in about 2 secs), and close a kind of small shutter with a very small servomotor (also a 2 seconds move). Of course all this will happen AFTER I cut the power, so I have to find a way to store enough power to do so, and after that shutdown the whole system to force the arduino to shutdown completely and restart from the setup() the next time I will push the switch.

From my research, I assume that 2 super capacitors should do the trick, but I am not very familiar with this kind of stuff and I am not exactly an electronic master.
What can I do?

2

look for a spring loaded dc gear motor.

power on and the motor opens.
power off and the spring runs the gears and shuts the blinds.

any battery could work. all you need to do is to stop powering the motor once the shutter is closed. no more drain on the batteries and all is good.

3

op's forgot about the lights.

first you must verify that they are dimmable. absolute must.
second, it might be easier to control the power source to dim them.

also adds a neat option.

on/off/on/off/on and they run at some dim level.

or each 'on' that occurs withing 1 second of the last off, is 10% dim from the last.
anything over 1 second off and they go off or full on, depending where the switch is after that 1 second timeout.

lastly, are you saying that the only power source comes from the power switch when the lights are turned on ?
and that there is no available power when they are turned off ?

still like the simple battery pack, charger and maybe a relay to remove all power from the arudino after the timeout.

4

for the motor, you mean make it stall? I think it is a bit reckless no? :confused:
I prefer properly command the servos after shutdown.
and yes, only one power source, the acdc adapter, and it will completely cut off when I shut the power.

btw I drew this:

the leds need to be feeded directly by the acdc output via a transistor controlled by the upper voltage divider, but for the other parts, what do you think?