Summary

Pops the balloon when the door is opened.
Based on your pin and door, it either blow when the door is opened or with some delay after it hits the floor.

See below for assembly and use instructions.

V1 is here. V2 may or may not be out there. There is room to improve it.

Post-Printing

Parts Joining

            <div><p>There are two holes for axis. In this version I kept it simple and less reliable and used a simple hole.<br>You may use 2mm drill bit to clear the hole and piece of filament as axis.</p><p>Then use lighter and melt the ends.</p></div>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/76/4d/08/ea/09/AxisJoint.jpg"></p>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/00/76/c0/42/bd/HeatSeal.jpg"></p>                <p class="detail-title"><strong>Add needle</strong></p>            <div><p>There is a tiny hole in the lever for that. If it is blocked, use a little heat to force the needle through. Let it protrude 2-3mm.</p></div>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/9f/82/a3/1d/f6/Needle.jpg"></p>                <p class="detail-title"><strong>Add magnets</strong></p>            <div><p>I used magnets on a steal door frame. Other doors may need other means. Not today.<br>The popper attached to the frame while the lever is activated by the door opening.</p><p>The magnets are 10mm diameter by 3mm height, with countersunk hole and simple countersunk wood screws. The holes are 2.3mm, so 2.5mm wood or 2.6mm would work here. Not a huge load here.<br>Don't overtighten, as you will crack the magnets. Clean the hole before installation from support leftovers.<br>Here are few magnets links:<br><a rel="nofollow" href="https://s.click.aliexpress.com/e/_c4dS3vhV">https://s.click.aliexpress.com/e/_c4dS3vhV</a><br><a rel="nofollow" href="https://s.click.aliexpress.com/e/_c3eRdWLV">https://s.click.aliexpress.com/e/_c3eRdWLV</a></p></div>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/93/ce/e2/09/ba/Magnets.jpg"></p>                <p class="detail-title"><strong>Usage</strong></p>            <div><p>Blow your balloon, three or four lungs, and tie it. Smaller balloons may not pop.<br>Slide it along the slit. Now the knot is kind of safety.<br>Now use a flat and blunt key to push the knot to the other side of the lever and your are ready to blow.</p></div>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/02/5e/5b/55/31/Slit.jpg"></p>                <p class="detail-image"><img src="https://cdn.thingiverse.com/assets/e8/62/d0/09/68/blow.jpg"></p>

Balloon popper - Door trap V1