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I have an idea for a safety coffin which is one of those graves with the bell on top in case someone is buried alive by mistake. I am thinking about how to make the bell ring. I know there are those with more electrical knowledge so I am looking for ideas. In general I came up with a couple of different ways. I could imagine putting a magnet on the bell and then using an electromagnet to move it. I know it is possible to even make an electromagnet but I am not sure it would have enough power to move the bell. I have also thought about a door lock actuator. My plan would be to use a simple PIR to activate it. I think a very short interval would be fine since I just want it to fire ring the bell and reset. If people set it off several times in a row it just seems like the person is more desperate. That means I had no plans for a controller. One question I had is if I can simply hook up the PIR to a 12V circuit and when it detects movement it closes the circuit. I must admit it seems almost too simple. I just wanted those with more knowledge to tell me if I am missing anything.
 

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Typical Ghoul Next Door
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I have zero mechanical ability, but I LOVE the idea. I think any subtle/creatively creepy and historical props are just fabulous!

I do think I've seen someone here make one of these before and it was really nifty...

https://www.halloweenforum.com/general-halloween/116608-where-term-saved-bell-really-comes.html

Found the reference! Mr. Grimsley started a thread on it back in 2008-09!
https://www.halloweenforum.com/halloween-props/72377-new-prop-effect-idea-dead-ringer.html

The tech guys in there go off on a tangent, but it's a fantastic one. The thread contains some absolutely amazing phantom footprints by some pretty talented home haunters.
 

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There are multiple ways that you could go about it, but I would use a string tied to the bell that is then tied to a motor rather than attempting to use a electromagnet of some kind. I think it would be quite difficult to find and even harder to control an electromagnet large enough to do what you are talking about.

If you have experience with writing code for Arduino boards or something similar there are several ways you could go about it using a simple relay board. If you don't have much experience you could get a controller board like this one: https://www.monsterguts.com/store/product.php?productid=17789&cat=249&page=1 that lets you record a sequence with a relay when the board is triggered. They sell a compatible PIR sensor as well. I would tie a string to the bell and then tie the other end to a wiper motor inside the coffin that got turned on for a few seconds when the PIR sensor detected a person was nearby.

Another completely different idea is to do away with the bell and instead have a voice from inside the coffin yell at people when they walk by. Things like "Hey! Let me out! I'm not dead yet!" You could do this using a PIR sensor and a board like this one: https://www.sparkfun.com/products/13720. This board can play one of several audio tracks each time it is triggered. The reason I mention this is that while I think the bell is cool idea and historically interesting, I don't think many people especially kids are going to understand what you are trying to convey. I will admit that history was my worst subject in school but I had never heard of the term 'safety coffin' before your post.
 

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There are multiple ways that you could go about it, but I would use a string tied to the bell that is then tied to a motor rather than attempting to use a electromagnet of some kind. I think it would be quite difficult to find and even harder to control an electromagnet large enough to do what you are talking about.

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String and a Reindeer motor. That is the approach I am trying to take but I am not quite done yet so while it is working fantastically in my head can't say if it will pan out yet.

Here is what I have so far.

I attached an old Shepard's hook that has been sitting in my shed since I purchased my house to a piece of wood which I plan to distress with some vinegar/steel wool mixture. I attached the bell, distressed with ammonia/salt, to the end of the hook with a zip tie, and attached a string, which i will probably replace with some fishing line so it is less noticeable to the bell and attached two eye hooks to the wood. One at the level of the bell, and another at the bottom of the piece of wood. I stung the string though the eye hooks and have it coming out at the bottom of the piece of wood.

IMG_0751.jpg

Here's what I am hoping will work.

I may have to replace the wood with a larger piece just to give it more height but, I plan on using a Reindeer Motor with maybe an irregularly spaced star cam. Sort of like a snail cam just with more high points. This might be hard to visualize but I plan to use a spring and a small piece of metal attached to the base of the platform (not shown) and have the string attached to it. The bell's striker will be positioned so it is touching the side of the bell closet to the piece of wood. The reindeer motor will pull against the spring, drop the striker towards the center of the bell, and when the cam releases it should hopefully spring back and cause the bell to strike.

Sounds great, but I have to see if it actually works.
 

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Funeral Crasher
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I haven't seen them in a while, but if you could attach a vibrating motor to the "pole" holding the bell, when triggered it would shake the bell violently enough to ring like crazy. That would also free you from having to use string.

You can make your own vibrating motor by attaching a half circle of wood/metal to the shaft of a fast motor. Probably at least 50 to 60 RPM.

Even this one might do:
https://www.ebay.com/itm/Small-Synchronous-Motor-TYD-50-110V-AC-50-60RPM-CW-CCW-4W-Torque-0-4Kg-cm/163123165138?hash=item25fae5f7d2:g:0nEAAOSwbVNbNfRn
 

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Ahh... Where the term "Dead Ringer" came from!

Hey he looks like that guy we buried!

They came up with these back in the day when they exhumed bodies and found scratch marks on the inside of coffin lids! They realized they buried people who were not quite dead. So they attached a line inside the coffin up to the bell so if they awoke and started ringing the bell passersby would hear be alerted. That person buried and come back from the dead was a "dead ringer"
 

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Ahh... Where the term "Dead Ringer" came from!

Hey he looks like that guy we buried!

They came up with these back in the day when they exhumed bodies and found scratch marks on the inside of coffin lids! They realized they buried people who were not quite dead. So they attached a line inside the coffin up to the bell so if they awoke and started ringing the bell passersby would hear be alerted. That person buried and come back from the dead was a "dead ringer"

There is an old urban legend that Mary Baker Eddy had been buried with a telephone in her crypt wired to a dedicated phone line and in the 1960s or 1970s some teenagers figured out the number and called it and everyone freaked out when it rang, but alas it is not true but if it was it would have been hilarious.

https://www.marybakereddylibrary.org/research/myth-a-phone-in-mary-baker-eddys-tomb/
 
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