I'm a complete newbie in anything related to electronics, software or hardware; yet with a couple of friends we're going ahead with an interesting project related to automation through wireless devices: more or less IoT but involving electric locks.
The case scenario: there's a room without any power outlets. It has a regular door. We want to be able to open this door through the internet, with a lock that lies inside the room, on the other side of the door; all this, given we:
Can't make any modifications to the door's structure.
Can't drill or make holes or whatever so as to get a power cable to the inside of the room.
But we can glue certain pieces behind the door, this is, inside the room that hasn't any power outlets.
We've planned, so far, to use an Arduino Uno; enhance it with WiFi features (i.e. a module or shield) so as to bypass the limitation of not being able to connect an ethernet cable; and glue a solenoid or lock to the inside of the doors, so that it acts as a second lock that can only be unlocked through the internet, accessed via Arduino.
Our ideal scenario would be opening this door remotely, from our home, even if this door is a hundred blocks away. If someone wants to get in, they should ask for our permission, as we don't control the built-in handle, but we do control a latch fixed on the inside.
All this setup should be powered with a long-lasting battery: we can't plug anything, and we can't risk getting our batteries depleted fast, because we'll never be able to open the door once again. We need these batteries to last long enough so as to be able to change them in a prudent time window; a back-up battery system should also work well.
Standard solenoid locks are 12v. Arduino powers 5v devices, not 12v ones, as far as my understanding goes.
We should open this door only 5 times a day. That's it; the remaining time in between, the whole device setup can well stay 'dormant', in low-energy consumption mode, only to 'wake up' when we give the order: "Arduino, please tell the solenoid to open".
We haven't specified which battery we would use; ideally, the most cost-efficient option. If it lasts 3 months and costs, say, 20 dollars -- well, we would love that.
I've done this really inaccurate, schematic drawing to illustrate our idea and research. I know there's many details missing but I wanted to prove our point:
(The Arduino should be positioned on the wall and not on the door! My bad.)
I hope I'm clear enough up to now.
The questions, then, are:
I've done some research, and I've seen that Arduino can be enhanced so that it consumes the minimum possible energy so as to remain 'aware', but not in full-power mode, which in our case would be unnecessary.
So, can we make Arduino super efficient in terms of power consumption, even if we attach WiFi functions, which, as far as I'm concerned, really takes on battery life? So that we can make Arduino run for months before replacing the battery?
Arduino can send only 5v; but the solenoid powers on 12v; then, getting a second battery to power our solenoid sounds straightforward, except that as far as my knowledge goes, this battery should last next to nothing (maybe I'm wrong here). And we want it to last for months -- if not, our door will remain sealed forever! Can I make the solenoid dependant on the Arduino, so that it's part of the "almost-no-battery-consumption" scheme, and battery lasts, as I would really like, some months? We would be talking of only one battery to power the whole set-up, instead of two that I guess that we'll need.
I'm a newbie, but can't Arduino power 12v through a relay or a transistor? Can't post links.
To clarify: Getting two batteries for our complete setup (one for the Arduino, one for the solenoid), if these two batteries both last, is not a problem; but it would be catastrophic to make a battery last long enough while the other depletes in 48 hours. The solenoid needs to get electricity a modest 5 times a day; that's why I believe we can make it super efficient.
With our friends, we've so far programmed Arduino to open a solenoid from the Internet. The solenoid we've used was 220v because we had it in stock; it won't be what we need for our project. It was just a trial. On top of this, the Arduino has no WiFi module, just an Ethernet shield.
There's a remaining problem to solve, which is: what would happen if the Arduino fails? The door would be sealed 'forever'. We'll tackle that issue afterwards.
TL;DR: we'd love to open a lock via WiFi: the lock and Arduino should run solely on batteries that last more than 48 hours: a couple of months would be ideal! Can we work this out?
Thank you very much for your help, opinions, and time. I hope my question is up to the standards.