Animatronic Hand Bell For Holidays

This is a project to build and program an electronic hand bell that uses the Adafruit Prop-Maker board for the built-in sound capability, battery charger, and accelerometer. The accelerometer monitors movement and a small high-fidelity speaker plays 19.1kHz mono .wav files. The effect is to create a hand bell that can play one note/ring/sound effect or many. Think of the Hershey's Kiss holiday ad where the Kisses play like hand bells to ring “We Wish You A Merry Christmas” but with a single bell and all you do is move the bell like you are ringing to the beat.

I was going to supply code but these projects aren’t that popular to spend a lot of time writing/debugging the code. Two other of my projects (Clausometer and Gort) use the same board and code is supplied with them than can be used as a guide. The Gort code is better than Clausometer if anyone actually builds a bell to program. Other examples at the Adafruit site - link below.

The Adafruit Prop-Maker is really only limited by your imagination. Details/references on how to code these projects are available at the Adafruit website. They are big into STEM projects and sell the hardware and have tutorials on how to program. School kids program these things and you can too! Maybe the closest code would be the Star Wars lightsabers but this bell doesn’t use the Neopixels.

https://www.adafruit.com/product/5768  Prop-Maker (also get the 500 mAh battery (#1578) and 40mm diameter speaker (#3968) too) (total cost around $33.)

https://learn.adafruit.com/adafruit-rp2040-prop-maker-feather All about the Prop-Maker and how to code for it.

https://learn.adafruit.com/search?q=prop-maker Example projects using the Prop-Maker at Adafruit (lots 3d printed)

Pushbuttons used are from Amazon.com: 1 SPST (12Pcs 12mm Self-Locking Latching Push Button Switch (Pack of 12) CYT1091, ASIN B075VBV4QH) and 1 NO momentary pushbutton (12Pcs 12mm SPST NO Reset Switch Push Button Switch (Pack of 12) CYT1092, ASIN B075VBWFM6) The latching switch is for power and the momentary is for menus, volume, or as you wish) They are just a standard size so you may be able to get them many other places too.

It's an easy print. I used Bambu Gold Silk+ PLA for the bell, Bambu Wood PLA for the handle, and Bambu Basic Black PLA for the bits inside the bell. The buttons can have their legends in different colors or black to blend in. They are separate parts you can set to whatever colors you want. I used m3x6 self-tapping sheet metal screws except for the battery holder which use m3x6 machine screws so they don't poke into the circuit board. Be careful about that - it's a possible trouble spot but easy to avoid if you watch for it. M3x6 machine screws have plenty of clearance. The PropMaker board is secured with two m2.5 screws. Be sure to clear the tiny amount of support out from under the dogs that hold the board at the connector block end.

The handle is attached with an m4x20 or similar long screw. The three little cylinder alignment pegs go between the handle and the bell in the three pockets. I used a small dab of silicone seal to lock the handle to the bell and not let it rotate any with respect to the handle.

The wiring is straightforward. Just refer to the photos. The power push-on-push-off latching pushbutton (red in the photos) is used for switching battery power on and off. Obviously the power pushbutton needs to be on to charge the battery using the USB port on the Prop-Maker. The momentary pushbutton is debounced in the Adafruit libraries and used to respond/select in the menus. Since the bell function uses the accelerometer, you can also use tapping, shaking, and/or position as inputs as well.

Hints on software - The way I was going on the code I wrote was to look at maximum acceleration in x-y and take that as the bell being at the extremes of the swing to play the wav file and using the magnitude of the acceleration to set bell volume. You can look for 1G in the Z axis and no motion on x-y to know it’s sitting to power down the peripheral power, etc. There is a momentary pushbutton you can use for menu functions if desired.

You can also have it sense a tap or motion and play something on its own. It can play mp3 files too so a little “Ring My Bell” by Anita Ward? Or, for Game of Thrones enthusiasts, use the sound clip where Hannah Waddingham follows Cersei through the streets of Kings Landing chanting “Shame”… Ding… “Shame”… Ding… Or any number of other clips and scenarios like the dogs barking Jingle Bells or using sound effects instead of bell sounds, etc.

The Prop-Maker is located in the bell such that the built-in accelerometer is located right on the long axis of the bell and handle and X-Y is oriented normal to that. X and Y motions are in the plane/sphere where you would swing the bell. Z is along the longitudinal/handle axis and would detect thrusting style moves like lunging with a sword in a fencing match. For most things in this application you may want to ignore the Z axis as it's just noise in swinging the bell.