Remote physical mailbox check


I am currently thinking about a remote (30/40 meters) mailbox alarm
It might use only what I have in stock so I m thinking in that solution :slight_smile:

temporary kicad schematic (image)

I know the emetter side one can be stolen but there are nearly no-risk here, in a private park.

Before I go forward on that idea I want to know

  • the concept is OK for that
  • the arduino model to use (I have unov3 & nano available currently)
  • is current consumtion a problem with this concept (boards limitations ?)
  • is this dispance OK for 433Mhz modules (after replacing the antenna maybe)

I also started to write code for each but I won't go further for now, until I know it is ok to do so.

why using a ultrasonnic sensor ? because I have few of them & because it will be on door panel so if letter is dropped from hatch it will detect it ; and if the local box is opened for a little package it will detect that as well as the main door opennning for larger ones too.

then I can make from distance inside the box on receiver side determinate what kind of mail it is (letter vs package vs maindoor has been opened).


Any suggestion ?
Anything I have not thought about ?
Is it ok ?
Is there any limitations on current I missed ?

This project has been passing here before. Do some search for Arduino + mailbox, or similar.

In fact I checked but not found any really similar-enough to be useful

Try again but search for part solutions that solves some of the questions.
The communication is one.
Powering is the second.
Detecting is the third.

Never expect to find exactly what You think about. Also be open for other angles of attack than Your first thoughts.

Of course, I won't get exactly similar needs :smiley: I mean here is currently 23:34 and still didn't find something similar enough to each question I mentioned, since maybe 18:30 or something... and my schematic has been done 2 days ago and if I came here it is because google on this was not “my friend” during these 2 days (few hours each only of course)

BUT no ; it is really not a leak of search and NO I am not just too lazy to search :wink:

I know I need to adapt things but I need advices before continuing I won't work in bad directions… :slight_smile: if I can avoid it

Currently, I have no choices on

  • Powering is done by battery because I can not have access to any kind of plug nor to the roof of the mailboxes zone

  • communication cannot (for version zero) be made buy another way (using parts I have in stock) so 433Mhz module

  • Detection .... here again is related to stock so ... ultrasonic sensor

so NOW Questions remains the same as the main post :innocent:

Before I go forward on that idea I want to know

  • the concept is OK for that
  • the arduino model to use (I have unov3 & nano available currently)
  • is current consumtion a problem with this concept (boards limitations ?)
  • is this dispance OK for 433Mhz modules (after replacing the antenna maybe) 

Until those 4 points are not answered (even partially) I won't go further :alarm_clock:

see that tomorrow

Battery powered is okey.
Being limited to "what's in stock" could be like going down a dead end road. Nevertheless, 433 ought to work.
Ultra sonics uses more power than f ex a microswitch especially 433. Not the best.
Concept.. What about time between battery changes/charging?
Use an Arduino using low power, has a sleep mode. However the ultrasonic will consume energy....
Current consumption depends on the consumers used. Your choice how often You like to change/charge the battery.
Not knowing everything about 433 I would say it's okey.

Yes, current consumption is an issue with both the UNO and Nano. Even in sleep mode, because of active circuits external to the MCU.

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Since the actual end application does not involve connection to a PC, a Nano is not really that appropriate (and I do not like the form factor of UNOs at all).

Receiver only is currently attached to the PC, yes.
:smiley: of course I won't put a PC in the mailbox :smiley:

Should it be a solution to use 2 separated batteries & control each one by a level measurement ?
Sending alarm for that ?

Or this idea is just ridiculous ? :slight_smile:

You can strip some components off a Pro Mini, then it will consume almost no current in sleep mode. You would periodically wake up, check the mailbox sensor, and transmit if there's any need. Then go back to sleep.

However, both the ultrasonic and 433MHz modules consume current in standby, so you would have to arrange to switch them off with transistor circuits.

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I ended up with the solution using an ESP32 but I hacked a dev board. What you learn is, the RS232 device chews up lots of power, so much so you don't want to keep it onboard. I used a single cell LIPO battery and a low-dropout regulator to make the 3.3V. It's been discussed above that a simple switch consumes the least power, which is what I used. The ESP32 has certain PINS that can wake it up from a deep sleep, so use one of those on your switch. Basically opening the door wakes up the processor, then I sent a text message to my phone saying "you've got mail".

a mini PIR sensor uses microAmps on standby. could be used to monitor the box. but it would be much more effect to have a switch close when the box is open or there is mail in the box.

There are low power options and, if possible, I would add a solar panel to eliminate changing batteries.

I published one such design here: Arduino NRF24L01 Mailbox Monitor/Notifier
I never thought of weighing the package in the mailbox, though.
But it looks like you’ve already bought all the bits for your chosen design so it is really a bit late to be asking for comments.

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I said I cannot access to roof to put a solar panel :frowning: else it would be aready done :slight_smile:

The mailbox does not have its own roof? :astonished:

the mailboxes room is not private it is for all , not mine, and it is forbidden to use the roof for any reason.

if you are only allowed to have a self powered unit, then lowest power use makes the most sense as does battery voltage monitoring.

a mechanical switch could power your device, and it would start, test power, send the message.
then time-out and shut off power. at that point, there is no power used.

If it will be powered on all the time, then the battery life will be less

it would seem that a simple way to change the battery will be key to make this project easy to use.

absolutly :slight_smile: I am currently thinking about it but I have not found an easy solution yet but to have a button inside to visualize current voltage each time I go & get my mails, with a physical switch on second battery & recharge it for next time

I thought that might be the critical piece of information missing from your original description and I like to make cryptic comments so we can (slowly and painfully) draw out the essential details. :face_with_raised_eyebrow:

And of course you are not allowed to use the mains outlet in the mail room (where they plug in the vacuum cleaner).

I foresee a problem will be the multiple layers of reinforced concrete in the floors between the apartment levels.