Triple Sensor Mailbox Alert really delivers

Playing around with the US Post Office is something we generally don't recommend. But if you create your own mailbox like [Bob] did, you have a much better chance of doing what you want without throwing up...

GB About: #Caturday Publish: 05/14/2022 Edit: 05/14/2022 Author: Gardener

Sensor Mailbox AlertBut if you create your own mailbox like [Bob] did, you have a much better chance of doing what you want without throwing any flags. Speaking of throwing up flags, one of the coolest parts of this project is the toy mailbox in the house that monitors the activity of the real box. When mail is waiting, the flag on the toy mailbox goes up. Once [Bob] has picked up the mail, the flag will automatically go back down. A magnet in the real box flag prevents false alarms on the toy box provided the Flag Raised On Outgoing protocol is followed. Best of all, it has emergency handling built in: if the mailbox door is open or the battery is low, the toy mailbox will wave its flag up and down. A magnetic reed switch on the wall of the real mailbox mates with a magnet in the flag. To determine if the door is open, [Bob] first used another magnetic reed switch on the bottom of the box. That didn't work well in wet weather, so he switched to a mechanical tilt sensor. An IR LED on the top and a phototransistor on the bottom of the box work together to detect the presence of mail. [Bobs] Homebrew mailbox has a fake back cover that hides a PIC 16F1825. When the door opens, the PIC wakes up, turns on a MOSFET, and checks the battery level. It waits two minutes for the postman to do his job and then reads the flag state. After comparing the states of the IR LED and the phototransistor, it sends a message to the toy mailbox indicating the presence or absence of mail. The toy mailbox includes a modified receiver board and servo to control its flag.

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