This is a safety coffin grave bell. If buried alive, you pull the string to ring the bell, and hope someone digs you out.
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The complete project is demonstrated and explained in this short three minute video on YouTube.
The board design and STM8 software are available on Github. DXF files for the roof truss and metal mounting brackets for the ultrasonic sensor and circuit board are also available on Github.
I decided to add some photos with the house lights up showing the basic construction of the project. It's mostly 1x4s with some 1/4" plywood for the roof and sides. Some short 2x4s are used internally at the top and bottom to mount the 1x4s used for the front and back. A single coat of some odd ball stain I had left over in the basement completes the look.
The base is constructed from some 1x4s. Despite the bell's small size, the mass and inertia are enough to shake the prop quite a bit. I use a dumbbell or some cinder blocks to keep the prop from shaking and to keep it from toppling over.
The sign is a sheet of 1/4" flat black acrylic with the saying cut from vinyl. A strip of white LED lights is inside a 45° angled aluminum channel with a white diffuser. The white LED lights were too bright so I slid a piece of red theatrical lighting gel between the LED strip and the diffuser.
The sign is mounted to some 1x2s. The lights are glued to a small piece of 1/4" plywood that's bolted to the bottom of the bottom 1x2. In this photo, you can see the red lighting gel.
This photo shows the inside of the roof. The metal trusses hold the roof to the main part of the prop. These have some 1x2s between them then the plywood for the roof is screwed to the 1x2s. An additional piece of 1x2 at the front hides the LED strips from view. I originally had a white LED strip but it was too bright. Rather than remove the white LED strip, I added a red LED strip next to it and disconnected the white strip. I used some red puffy t-shirt paint to glue the LED strips to the roof.
The final photo shows the 2x4s at the top of the prop. These are about 6" long each and are used to support the front and rear 1x2s.
Glen Akins
