Mailbox detector, what is the most battery efficient sensor?
-
I know there are some sketches already made for mailboxes, but if I remeber correctly most of them where built for U.S style mailboxes. I live in Sweden and most mailboxes mostly looks like "boxes" where you lift the lid from the top.
I would like to place a sensor in the lid. First I was thinking that I could use a triple axis sensor
But would that sensor be a good option? I would want the arduino to sleep 99.9% of the day and only register the 1-2 openings /day of the mailbox. I want the battery (2xAA) to last for a year atleast if possible.
-
A simple magnet switch should suffice. Works fine in my mailbox.
-
if you have a mailbox with 2 hatches, install 2 magnet switches.
one sets the "mail is waiting"-signal (postman put mail in box) and if you open the mailbox to take out the mail, the second sensor resets the state. Really comfortable
-
Magnetic switch or tilt switch (ball or mercury) would be a safe bet. Other possibilities would be a mechanical switch either at the top or bottom (that reacts to the weight of the mail). A light sensor / resistor (which obviously wouldn't work at night) or perhaps some sort of IR beam (not very battery friendly I imagine).
Personally I have been using tilt switches for a couple of years. Very jumpy though when it comes to debouncing. Never tried with a capacitor as a simple hardware debouncer but rather just run the tripped message every loop and then sleep at the end of the loop, first for 10min and then until the next interrupt. Domoticz sets the sensor as "off" automatically after a time. A bit hacky but it works it seems. Reading the tilt switch state and getting it right every time became too frustrating.
Speaking of debouncers, I was almost desperate enough to look into debouncer ICs like the Maxim MAX6816/MAX6817. Almost.
A bigger concern is perhaps radio range. Despite earlier trials that seemed to indicate that the range was ok (and activating ACK), I had to set up a repeater node (with a pa+lna no less, the normal module wouldn't work!) and manually make sure the mailbox node always sends through the repeater. I was planning to set the repeater up eventually anyway, this just forced my hand.
