intelligent mailbox sensor

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Omar20

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hi dear friends i would like your help please i want to know which sensor is suitable to sense the availability of a letter inside the mailbox. what i mean is i want to design an intelligent mailbox that can sense the availability of a letter when dropped inside it. so when the post man drops a letter inside the mailbox the mailbox will sense it. so which sensor i can use to achieve this objective?
 

My mailbox is about 50m from my house and out of sight. I bought a mailbox with a hinged lid and fitted a magnet to it, on the box is a red switch wired back to the house. When the lid is llifted, the switch opens and a LED lights indoors. So it doesn't detect if mail is present but it does detect if the mailbox lid was opened by the postman.

Brian.
 

I made few years ago a prototype using infrared LED and IR receiver. So the mail interrupts the infrared light getting to to receiver, which can trigger RF data transmission. This clearance can be checked e.g. every 5 minutes to save power.
I quit the project because I wasn't able to minimize the current consumption for it to run atleast 6 months in extreme -20-30c temperatures we have here.

Here's Ben Heck show about the similiar project.
https://www.youtube.com/watch?v=x7AiV7yg-yw
 
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You can put sensors on the letterbox door in the form of magnets and reed switches to detect the letterbox being opened.

Or perhaps if you have no door to the letterbox and the box has light shining into it then you can put an optical sensor in that detects when the light has gone because the letter is laying over it.

Or you can do something else - a lot depends upon the mailbox itself.

Explain yourself more and we wont then be making wild guesses.
 

Here are pictures of my mailbox switch and the box in the house that records when it is opened and a load of other things too. The LCD shows time, date and swimming pool temperature (it's an outdoor pool and mid winter here!) followed by three lines showing the latest recorded events and their times. The yellow LED lets me know at a glance if I have mail.

Brian.

 

**broken link removed**
this is the mailbox i am going to use see the
 

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Thats similar, the lid lifts up on mine and your seems to have a slot but you should still be able to mount a small magnet on the flap and a reed switch nearby.
I used a tiny magnet removed from a dead CD drive, there is one behind the laser lens in the focussing assembly which is powerful but small. I glued it to the lid and mounted a reed actuator on the mailbox body so they are in close proximity when the lid is down and the switch opens when the lid lifts 1cm or so.

Brian.
 

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