Hello everyone,
I am building a new house, and I have bought this letterbox. As you may notice, there is no way to tell if a box or letter has been delivered, so I look forward to installing a low-power device to identify if something has arrived.
My idea is to use two devices:
one inside the letterbox, with two switches (one for the top door, one for the bottom), a very low-power chip (like ATtiny-something), a board to transmit the signal to the second device, and a battery
one inside the house, within a rack, which has to receive a signal every time one door has opened and send the data to some service (I don't know if I'm gonna use a database or a telegram bot - anyway, it's irrelevant)
The problem relies on the fact that the letterbox is "on an open field", and the receiver will be within the garage, behind 25cm of armored concrete, and around 30m away from the letterbox.
My questions:
Is it better for me to use an RF system or a WiFi system? Pro and cons?
Any advice on achieving low power consumption?
Please note that am not an ArduinoPROuser (I have only created a project that aims at showing the PID control on a DC motor with an encoder), and all my knowledge of everything I have written in the previous paragraphs comes from 2 days of internet research.
I am not in a rush, I have 2-3 months before the house is complete, thus I have all the time to learn everything.
You'll find stacks of such projects, including one from me: Arduino NRF24L01 Mailbox Monitor/Notifier
The main issues are battery life and radio range. Also reliability of the sensor may be important. You may have to do some experiments with the radio type to chose a suitable one.
Lots of people assume a definative answer can be given to such questions;
"the receiver will be within the garage, behind 25cm of armored concrete, and around 30m away from the letterbox"
Unfortunatly there cannot be a definative answer, because the construction of walls etc varies so much.
WiFi might work, but wont be low powered, when compared to RF Systems. An RF system could probably be woken up by the switch on the letter box and send an alert within maybe 50mS to 100mS, so its not powered for long.
Several RF systems to shoose from, the NRF24 is one example and the range of that module might be enough, despite the walls.
LoRa is by a long range (pun intended) a better bet, far longer range capability than the NRF24 and capable of far lower current consumption too.
But, ultimatly, only you can answer which module is needed as only you can test it in situ, as in real World.
Have a switch activated when something is in it , and flash an led on the top.
You could use a cheap car remote to send your signal ( eBay) wirelessly back to some form of indicator ( which might be Arduino).
I used one on the cat flap as I didn’t want wires across a door - runs for years and will signal through my garage wall.
There might be a mechanical solution ( look at mouse traps ) .
I'll definitely have a look at your project @6v6gt
You're right @srnet, actually, I am looking for bits of advice, rather than the perfect answer. Indeed, based on your massage I can discard WiFi, and focus more on RF and do some tests on my own, maybe starting from NRF24 and LoRa!
Nice idea @hammy. The idea of the light is the least attractive but is a possibility. In fact, if I come home by car, I must pass in front of the letterbox, thus I will see the LED.
Penetrating all that concrete with wi-fi won't be easy (higher frequencies don't penetrate as well). But I'm not sure the power consumption would necessarily be a problem. The MCU could spend it's time in deep sleep or completely unpowered until one of the letterbox doors is activated.
But if you can use wi-fi, there could be some advantages to that. You might not need another device in the house/garage if you can get notification on your phone.
Yeah, I know that WiFi is RF, I was trying to oversimplify
As per "the other device", I think that I will use an Arduino Uno in the garage to receive data and maybe interact with a third party to share the trigger to my phone.
Indeed. I did a mailbox notifier for a friend using a Lolin (Wemos) D1 Mini, which has an ESP8266. It connected directly to the router on 2.4GHz, and from there to IFTTT. So no additional device was needed inside the house. I actually used the D1 Mini Pro, which has an external antenna connector. It was completely powered down until the box door was opened, and then shut itself down after the 15 seconds or so needed to transmit.
Of course 900MHz, or even 433MHz, would go through walls better than 2.4GHz, but those frequencies might also be subject to more interference from other broadcasting devices. I don't have much experience in that area, Perhaps others here do.
But I would suggest the OP consider something a lot simpler that requires no radio or batteries. All you really need is something that's visible when you drive by that tells you if the box has been opened. Perhaps something tied to a string that you stick between the door and the box frame that will fall out when the door is opened. I've always found it strange that manufacturers of mailboxes didn't include some kind of physical flag for this purpose. Anyway, you don't really need notifications on the phone anywhere in the world - because you can't retrieve the mail unless you're at home. So just rig up something physical that tells you the door has been opened.
