Ringing Bell Topper for Pinball Machine

Makers who build their own pinball machines often add "toppers" for added attraction. This project builds a Bell Topper, styled after the one on the Fire! pinball machine (Williams, 1987). The bell is electrically actuated to ring at the appropriate time as controlled by the machine. But this bell could also be used anywhere you want an interesting looking, electrically operated bell.

Handbell (about 4" diameter & 3.5" tall excluding handle)

Small solenoid (JF-0826B)

Aluminum bar stock (about 2mm x 25mm x 36")

Diode (e.g. 1N4007)

Spacer material (wood or 3D printer filament)

2 bolts & locking nuts (e.g. M5 x 10mm)

6 wood screws (e.g. #8 x 3/4")

2 solenoid mounting bolts (M3 x 5mm)

Remove the clapper using pliers. Unscrew the handle. Save the brass nut, threaded rod, and washers.

Make one center piece and 2 side pieces, with dimensions shown in the diagram, from aluminum bar stock. The bends are about 60 deg but the exact angle is not critical. I used a vise, and bent the bars by hand.

Drill holes to match your bolt size, about 5 mm or 1/4." For the center bell mounting hole, drill a 7 mm or 5/16" hole to match the threaded rod diameter.

Use M5x10mm (or similar) bolts and locking nuts to assemble the frame as shown. Adjust bend angles (with pliers or by hand) so that the frame rests flat on a table, is symmetrical, and is about 4" tall at the center.

Cut a 1.5" section of threaded rod with hacksaw. Mount bell under frame with brass nut & threaded rod. Washers can be used to adjust height as desired. Bottom of bell should be about 1/2" above surface.

The spacer securely mounts the solenoid onto a surface, at the proper height and distance to strike inside the rim of the bell. For the prototype, I needed 1/4" of height. The solenoid has 10mm of travel, so plan for the solenoid shaft, which will be our clapper, to be about 7 mm from the inside of the bell.

I used a 3D printed part (file attached) that holds the solenoid and conceals the electronics, but a simple 1/4" thick wood spacer might be used.

Test fit the solenoid and spacer under the bell to verify it is positioned correctly.

If the bell is to be connected to a solid-state driver, then a flyback diode is required across the solenoid leads. Solder the diode across the solenoid leads and insulate it with heat-shrink tubing or electrical tape. This solenoid is not polarized, so it doesn't matter which way the diode is attached. But the lead connected to the striped end of the diode will become the positive lead. Label the positive and negative leads.

Bolt the solenoid to the spacer and route wires through the channel.

Note: I used a JF-0826B-12V solenoid which draws 2A and makes a fairly loud bell! If loud volume is a concern, there are 1A (JF-0837B-12V) and 0.4A (JF-1040B-12V) versions available.

Caution: these solenoids are designed to be energized for just a few seconds at a time. That's fine, since for our purpose we will use a 60ms pulse.

Separate and lightly sand the aluminum frame pieces with fine 220 grit sandpaper. Apply spray paint to the frame following the paint manufacturer's instructions. A combined primer & paint is recommended. Several thin coats look better than one heavy coat. Optionally, spray a protective clear coat. Reassemble frame and bell after the paint is fully dry.

Use 2 wood screws to mount spacer to top of backbox. Use 4 wood screws to mount frame to backbox, positioned over solenoid.

Use additional wire as needed to route the positive lead to +12VDC. Optionally, insert a 5A fuse in this line.

Route negative lead to the controller output port. The controller will ground this line to activate the solenoid.

Test operation. Use a 60ms pulse. The bell may be moved up or down with washers to adjust for stronger or weaker impact.

Congratulations, now you're ready to setup your pinball machine to ring the bell! Have fun.

Pinball controllers are designed to switch large currents and can easily handle this 2A solenoid. For other microcontrollers, use a power boosting circuit to drive the solenoid. An example circuit using an Arduino can be found here.