And I’m trying to find a way to accurately detect if it currently holds mail or not.
I’ve tried many things, but nothing really works reliably. Just to name a few:
Sensor that detects when the lid is opened
False positives when I quickly check for mail by looking through the lid.
False positives because the mail man often opens my letter box even if he doesn’t put in any mail.
Laser barrier sensor at the top
False positives because sometimes the paper boy shoves a new paper in there and then pulls it out again when he sees the “No newspapers or ads!” sign.
Laser barrier sensor at the bottom
False negatives because sometimes a letter or small package gets stuck at the top
Laser barrier sensor beaming from top to bottom
False positives because sometimes a small letter ends up on the side where it doesn’t block the beam
Ideally, I would like to have a cheap low power device that scans the letter box whenever it detects vibrations. Maybe this can be done reliably using mmWave?
You need a sensor that can detect a letter in the box and then you need to have multiple check for a detection over time.
The multiple checks should solve many of the false positives and laser, ultrasonics, hall or whatever should Matter less then, as long as it is detection of the letter in the box and not the action of putting it in.
