Melodic Chimes
Melodic Chimes is a stringed instrument playing melodies by automatically adjusting string tension to create notes.
Melodic Chimes is mounted to a wall and is roughly 10.5" wide by 23" tall.
The faceplate changes colors depending on the string being played.
The strings are wrapped around brass adapters with diameters selected to balance tuning speed and torque requirements.
The plectrums are designed with geometry to pick the string and quickly move away with enough of a gap to prevent string buzzing. The plectums can be lowered or raised to decrease or increase the pick intensity which in turn changes the volume.
Custom made single coil pickups were wound using my Coil Winder to balance size and waveform intensity.
Sound holes help project the sound from the sound box and the chimes have enough volume to be audible without amplification.
Bridge are made from bone to help transfer vibrations to the sound box which is mechanically isolated from the frame in an attempt to louden the chimes.
Underneath contains the plug and power switch.
On the side a SD card is inserted that stores MIDI files.
This top corner view reveals a slot for a programming cable.
The touch display is used to select the song, change the pick volume, calibrate the strings, and more.
The backside reveals the magic.
Just an angled shot.
The PCBs to the left and right are the chime controllers, where each controller interfaces with one or two of the tuning steppers, picking steppers, the volume steppers. They also process the signals generated by the pickup coils
The Teensy 3.2's are responsible for converting the pickup coil's signals into freqencies which in turn is fed into a p-controller that controls the tension stepper to match the string's vibration frequency to the desired note frequency.
The LM358 op-amps amplify the pickup coil signals to a voltage level the Teensy is capable of processing.
Three 5:1 gear head NEMA 17 stepper motors are used to provide enough torque to tune the strings which require 2LBS to 12LBS of tension.
The plectums are powered by NEMA 14 steppers that are decently small and provided smooth and silent rotation. The plectum hoppers are spring loaded and rise and fall using the round steppers.
The pickup coils are bottom mounted to this cross bar.
The sound box is just that, a box. The four machine bolts can be removed to isolate the sound box from the frame since the box is glued to the horizontal mounting bracket with a neoprene interface.
The main controller is a ESP32 Dev. Kit V1. A future firmware update will use the WiFi to fetch network time so the chimes can play on the hour.
The SD card slot is a generic break out module connected to the main PCB.
A Mean Well LRS-50-12 power supply provides more than enough power.
The main PCB schematic is straight forward using mostly premade modules to reduce the time to design and assemble.
The Chime Controllers are also straight forward but with more bypass capacitors that are required to reduce noise on the pickup coil lines due to the close by stepper motors.
The PCBs were created using DipTrace...
...and fabricated using JLCPCB.
Musescore 3 was used to compose a few melodies using three instruments, one for each string.
An inexpensive MIDI keyboard was a significant help the composition process.
Faceplates, brackets, and the sound box was cut from 3mm acrylic and wood using a laser engraver. Parts were designed in AutoCAD.
3D printed parts were printed in PLA and modeled using Fusion 360.
The wall mounting bracket is sturdy and allows the use of a drywall screw for peace of mind.
I hope you liked this project, it's in my top favorite projects. As a Covid pandemic project, I learned new skills and stayed sharp.