Mailbox notifier with magnetic sensors

Discussion in 'The Projects Forum' started by dbernard, Feb 8, 2016.

  1. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    Hi

    I would like to be notified by a light when someone puts something in my mailbox. I would need 2 magnetic sensors (or switches). I was told I can use a 555 timer for this. The objective is when someone opens one of the 2 mailbox doors it triggers and turns on a led. I can see the led from the house. This can only be turned off by a manual reset push button. Battery operated is best. Thanks
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    Readily doable.
    A 555 will draw a significant standby current (even the CMOS version can draw up to 250uA). For prolonging battery life I'd use a CD4013 as a latch instead.
    How far apart are the mailboxes?
     
  3. #12

    Expert

    Nov 30, 2010
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    I would use a mechanical method. If you want to use a magnet, use it to hold a colored piece of sheet metal out of sight until the door is opened. Opening the door moves the magnet away from the sheet metal and it drops into view.
     
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  4. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    Hello, thanks for the info, but I am not that qualified to understand the difference.
    It is actually one mailbox. It has a door that can be opened completely as well as a opening in the front with a lid.
    Attached picture, might be easier to explain. They both open from towards the outside.
     
  5. #12

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    Too simple. Connect the positive voltage to two normally open reed switches, and they are in parallel with each other. If either switch loses its magnet, it closes and allows current through a resistor to fire an SCR. The SCR grounds an LED circuit. Then add a reset switch, normally closed, in series with the power supply. You must press the reset switch when the doors are both closed.
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I would go with an optical based system being envelopes and magazines are typically light colored or glossy and easy to differentiate between a dark flat black colored mail box bottom with simple photo sensors.

    The rest is just a matter of how efficient you want the system to be.
     
  7. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    Optical is not the idea. I played with that one since it was easier for me. The problem was when either a letter does not fall directly on the floor (and cover the photo sensor) or a smaller envelope.
    The way to go is with as #12 says. Can you help me design this ?
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Having seen your letterbox pic, unless the post-person has a key won't you need only one switch, to monitor the top slot opening?
     
  9. tcmtech

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    If you are close enough to your mailbox to see a indicator LED can't you just walk out there in the afternoon and check it or am I missing something obvious? o_O

    BTW a photo sensor based systems can use reflection from the top down or back to front to see the whole inside of the mailbox and thus detect any change in the average light being reflected.

    Semi passive IR detection is also very good for that sort of monitoring of an area rather than a specific spot like light beam brake detection is.
     
  10. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Working backwards, make the LED blink. It is more noticeable at a distance and cuts display power significantly. A very bright LED with 10 mA continuous uses 0.6 mA-s, milliampere-seconds, of battery current in one minute. The same LED hit with 50 mA for 10 ms every second uses 0.03 mA-s, a savings of 95%.

    To get more power savings, use the energy stored in the flasher timing capacitor to light the LED. This is common in joule-thief circuits.

    As much fun as that circuit would be, I agree with #12 about a mechanical approach. A white square of shirt-board tied to the mailbox with a string, and a small solenoid capacitor-coupled to a magnetic reed switch (normaly closed, held open by the magnet on a closed door) could do this with zero steady state current in both the set and reset conditions. I'm envisioning the solenoid strikers in chime-style doorbells. Those rely on AC for the proper striking action, but DC plus a capacitor will act the same. The flag is hanging on a pin, and the solenoid knocks it off the pin so it falls down and is swinging in the breeze.

    ak
     
  11. #12

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    I was in a cast for 13 months with my leg broken in 6 places and suffered amazing amounts of pain using my crutches to go to the mail box. I would have preferred not to go through that pain and struggle if there was nothing in the mail box. The Thread Starter might not be that bad off, but he is the sole judge of whether his reasons are sufficient to do the work this project requires. (You cruel, heartless person.)

    You can take the rest of the week off from running amok and pillaging. Your reputation is secure for now.;)
     
  12. tcmtech

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    My mailbox is about 3 blocks from my house so I just pick my mail up every week or two/whenever I feel like it. :p

    BTW I wasn't born cruel and heartless. I had to work at it. :D
     
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  13. hp1729

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    Nov 23, 2015
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    I might use a blinking multi-colored LED. it draws about 0.5 mA. I got mine from Electronic Goldmine. They have lots of such things. I ran one off of a CR2032 for a week before giving up. So you would be looking at a circuit that runs off of 3.0 V.
    The switches are SPDT reed switches shown in a position with the magnets close. Also available from Electronic Goldmine.

    Something like this. Part numbers Gxxxxx are Electronic Goldmine.
     
    Last edited: Feb 8, 2016
  14. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    Wow, thanks for all the ideas, I really like the part of a blinking led.
    Now to give some background so that my project is better understood. The mailbox is located in France. It is a about 50m from the house in a direct line of view. In France all delivery services have a master key to all French mailboxes, so they can open for packages or slide for letters, thus the 2 sensors. I prefer the magnetic sensors. I can get up to 5-6 deliveries by different services a day. They delivery from 8am until 6pm, You have to wait all day. Sometimes they show up unannounced and just drop it off in your letter box as early as 9.30. Yes, I can go every 1hr to check, but it would be easier with a circuit. From that time on, I can do anything else and don't have to wait all day and no longer have to wait for nothing
    Also, I am a beginning novice at electronics so any help is much appreciated.
    Thank you
     
  15. hp1729

    Well-Known Member

    Nov 23, 2015
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    50 m? May need a brighter LED. I suggest you buy an assortment and see the results. Will the postal delivery person get concerned if he/she opens your box and finds electronics?
     
  16. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    I was hoping it would be discreet enough so it won't be so shocking. But good point.
     
  17. AnalogKid

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    Who "owns" the mailbox?
     
  18. #12

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    There are some spectacularly stupid people in this world. If a school principle and the local police force in a Texas city can mistake a clock for a bomb, other people could think any blinking light is a bomb.
    Never underestimate the ingenuity of fools.
     
  19. hp1729

    Well-Known Member

    Nov 23, 2015
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    Out here in the "colonies" we just put a mechanical flag on the side of the mail box.
     
  20. dbernard

    Thread Starter New Member

    Feb 8, 2016
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    I own the mailbox. Try teaching a Frenchman a new trick :)
    The mailbox has 2 sides, the back (the door I can see from the house (not on the picture) will have the electronics, light and reset button. The front will have the magnetic sensors but discreetly inside.
     
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