What is simplest possible circuit for letterbox flap "open" detector?

[MM]

It's probably quite easy to make a small plunger from scratch, using small tubing or things that can be used as tubes. At QD (shop chain in Lincolnshire) they have a whole range of yellow boxes with assortments of screws, nuts and, yes, SPRINGS! They even do an assorted set of rubber washers, I believe, which could double up as insulators.

In fact, the more I think about this the better I like it, because it would not require any electronics of any kind (except the battery, plunger, wire and buzzer or bell). Dunno quite how to mount a plunger on the letterbox flap, though. It must not provide any resistance to opening the flap, else the postie will leave stuff sticking out.

MM

[MM]

Not sure whether he can read... certainly dozy enough to deliver the wrong mail to me, or my mail next door sometimes. Plus, not ring the bell when necessary. Once he handed me a packet that clearly needed signing for, so I asked, shall I sign then? And he said with a grin, nah, that's okay. Couldn't be bothered to dig out his doubry and stylus. (Maybe he'd forgot to being it.)

MM

[HarpingOn]

There's software called 'motion' on Linux that I use with a Pi and a camera module to use as a security camera. It can be made to notify of an event, which is a detection of motion. Could easily get motion to toggle a gpio on the pi board to make something external happen, light, sound, whatever. Or, indeed just use the audio out on the Pi and make it chirp, howl, whatever.

[jimekus]

Having a separate street entrance I have to make a special effort to enter through another gate where the mailboxes are. I used a rubber band stretche d across the top of my mailbox opening with a doubled-ended clothes peg tha t grabs hold of the middle of the rubber band. When mail goes in the clothe s peg is pushed back and, under pressure it flips up to the roof of the let ter box. I can see the front of my letterbox from the door of my apartment about 30 meters away and can tell whether the clothes peg is up or down. Un fortunately my 720p webcam doesn't have enough resolution. By attaching a t iny LED to the swinging end of the clothes peg I got its terminals to make contact with the +ve and -ve surfaces of two cr2032 batteries which I taped to a connector on the roof of the letterbox. How can I eventually make thi s into a Bluetooth circuit?

[Brian-Gaff]

Well, you used to be able to get normally open or normally closed read switches. they were often used in those little blocks mounted on opening windows. One had the switch the other a bar magnet. When the window was opened the magnet was taken away from the switch and it either opened of r closed the contacts depending on the type. All you would need was some low current circuit operating a larger relay which had a parir of contacts used to make it latch on when it was energised, the other pair of contacts would operat the sounder. Tto cancel the alarm just have a push switch to break the contact in the latching circuit when you had retrieved the mail.

I've done this with an old garage door and it worked fine till the dorr got stuck one day...

Still the principal is the same. No need to mess e with complicated electronics, jui ust simple dc circuit powered by a cheap DC 12 volt wall wart. Brian

[tabbypurr]

or just reed switch, LED & resistor.

NT