This is another from my smart home makeover attempt, I wanted to get info when new message arrive to my old school mailbox.
I tried a lot of radio transmission technologies and frequencies, best came 433mhz door sensors from secrui. It can send 4 different radio codes, Open, Close of contact, tamper switch, and low battery.
The problem was, after placing sensor into steel mailbox, it acted like Faraday cage and no signal made it through.
So I designed this to-be-3D-printed door which can let the signal out.
It is meant to hold PCB from secrui door contact, modified little, tamper switch was replaced by end stop switch, attached at the bottom of door. This sense the taking out of mailbox, and then I made extension to reed switch, which is placed in reef switch holder, and installed near front door where the mails coming from. On front door I glued small magnet which is switching reef switch.
As simple as that. On the other side, I am reading radio signals through OpenMQTT gateway with 433mhz RF receiver currently, but I have in plan to switch this to ESPhome with the same hardware. But this is beyond scope of this project ( I am available if someone needs help however )
Door itself will fit in most bulk mailbox used mainly in Europe, Germany, Slovakia, Poland, Czech republic...
Door sensor http://s.click.aliexpress.com/e/bRkvUATW
Limit switch http://s.click.aliexpress.com/e/c98gRNIu
Reed switch ( the black are made from plastic instead of glass and is more rigid) http://s.click.aliexpress.com/e/cLS42Vwu