Project

# Title Team Members TA Documents Sponsor
42 Position-Sound Accurate Electric Snare Drum
 Kadin Shaheen
Oscar Li
Tim Dager
 Aniket Chatterjee
Team Members:
Tim Dager (timcd2)
Kadin Shaheen (kadinas2)
Oscar Li (hongyil9)

Problem

Modern electronic snare drums are unable to replicate the detail of sound that changes continuously based on how and where you strike an acoustic drum. They generally relegate hits to one of three zones: head, center, or rim, with some degree of velocity sensitivity. The issue with determining strike zones through dedicated zone sensors is a limited resolution sound profile.

Our goal is to develop a digital snare that utilizes time difference of arrival (TDOA) with piezoelectric sensors to pinpoint drum strikes to a centimeter level of precision to realistically emulate the sound profile of an acoustic drum. Further positional detection improvements and low-latency benchmarks will be treated as stretch goals.

Solution

We will utilize three piezoelectric sensors with analog processing components feeding to an STM32 microcontroller to measure and calculate strike position. The piezos will be placed equidistantly from the center of the drum mesh and will detect the first arrival of a wave to triangulate the strike position. Signal processing will account for reflected waves from the rim of the snare drum as well as attenuation across the mesh. The STM32 microcontroller will be used for its DAC module, digital signal processing, and communication through USB as a MIDI device. The drum pad will divide into four subsystems including the piezo sensor array, analog pcb, MCU, and power subsystem.

Solution Components

Subsystem 1: Piezo Sensor Array

A set of concentrically spaced, commonly available piezo vibration sensors will be mounted to an inexpensive single zone mesh drum. A minimum of three sensors are needed to perform the time difference of arrival (TDOA) algorithm, but more may be added (while maintaining concentricity) to allow for cross referencing if necessary. The placement of these sensors will mimic implementations of TDOA systems in similar applications.

Subsystem 2: Analog PCB

An analog preprocessing board will take inputs from each of the piezo sensors, and convert them into usable analog inputs in the range of the microcontroller. It will consist of an op-amp as an impedance buffer for each piezo, a voltage translator to align our analog signal with the specification of the microcontroller (0 - 3.3v for STM 32), and a clamping circuit to protect from voltage spikes.

Subsystem 3: MCU (computation + data output)

An STM32 with a 12 bit ADC will be used to accept the three analog signals, perform the TDOA algorithm to compute a positional estimate, and generate the appropriate usb signals as MIDI, that the user may use for triggering drums, or other purposes.

Subsystem 4: Power

The power subsystem will take input from a USB source and output correct voltage levels to the Analog PCB Subsystem and to the MCU. The device will be powered from a 5V USB input with USB-C preferred. A 3.3V onboard regulator will generate the primary logic and analog supply rail for the STM32 microcontroller and other 3.3 V compatible components.

The subsystem will include input protection, local decoupling/bulk capacitors to maintain a stable 3.3V rail. If later component selection requires an additional power supply voltage for the analog subsystem, or other circuitry, an additional regulated rail may be added.


Criterion For Success

The drum must be capable of distinguishing between a minimum of 10 distinct radial zones, each of which may be mapped to different midi notes to confirm zone accuracy
Drum pad USB device endpoint is recognized as a MIDI interface
Net latency measured from impact time to USB handshake should be minimal enough to avoid causing an audio-tactile mismatch (delay between strike and sound) sensed by the player- roughly 40ms.

Tesla Coil Guitar Amp

David Mengel, Griffin Rzonca

Featured Project

# Tesla Coil Guitar Amp

Team Members:

* Griffin Rzonca (grzonca2)

* David Mengel (dmengel3)

# Problem:

Musicians are known for their affinity for flashy and creative displays and playing styles, especially during their live performances. One of the best ways to foster this creativity and allow artists to express themselves is a new type of amp that is both visually stunning and sonically interesting.

# Solution:

We propose a guitar amp that uses a Tesla coil to create a unique tone and dazzling visuals to go along with it. The amp will take the input from an electric guitar and use this to change the frequency of a tesla coil's sparks onto a grounding rod, creating a tone that matches that of the guitar.

# Solution Components:

## Audio Input and Frequency Processing -

This will convert the output of the guitar into a square wave to be fed as a driver for the tesla coil. This can be done using a network of op-amps. We will also use an LED and phototransistor to separate the user from the rest of the circuit, so that they have no direct connection to any high voltage circuitry. In order to operate our tesla coil, we need to drive it at its resonant frequency. Initial calculations and research have this value somewhere around 100kHz. The ESP32 microcontroller can create up to 40MHz, so we will use this to drive our circuit. In order to output different notes, we will use pulses of the resonant frequency, with the pulses at the frequency of the desired note.

## Solid-state switching -

We will use semiconductor switching rather than the comparably popular air-gap switching, as this poses less of a safety issue and is more reliable and modifiable. We will use a microcontroller, an ESP 32, to control an IR2110 gate driver IC and two to four IGBTs held high or low in order to complete the circuit as the coil triggers, acting in place of the air gap switch. These can all be included on our PCB.

## Power Supply -

We will use a 120V AC input to power the tesla coil and most likely a neon sign transformer if needed to step up the voltage to power our coil.

## Tesla Coil -

Consists of a few wire loops on the primary side and a 100-turn coil of copper wire in order to step up voltage for spark generation. Will also require a toroidal loop of PVC wrapped in aluminum foil in order to properly shape the electric field for optimal arcing. These pieces can be modular for easy storage and transport.

## Grounding rod -

All sparks will be directed onto a grounded metal rod 3-5cm from the coil. The rest of the circuit will use a separate neutral to further protect against damage. If underground cable concerns exist, we can call an Ameren inspector when we test the coil to mark any buried cables to ensure our grounding rod is placed in a safe location.

## Safety -

Tesla coils have been built for senior design in the past, and as noted by TAs, there are several safety precautions needed for this project to work. We reviewed guidelines from dozens of recorded tesla coil builds and determined the following precautions:

* The tesla coil will never be turned on indoors, it will be tested outside with multiple group members present using an outdoor wall outlet, with cones to create a circle of safety to keep bystanders away.

* We will keep everyone at least 10ft away while the coil is active.

* The voltage can reach up to 100kV (albeit low current) so all sparks will be directed onto a grounding rod 3-5cm away, as a general rule of thumb is each 30kV can bridge a 1cm gap.

* The power supply (120-240V) components will be built and tested in the power electronics lab.

* The coil will have an emergency stop button and a fuse at the power supply.

* The cable from the guitar will use a phototransistor so that the user is not connected to a circuit with any power electronics.

# Criterion for Success:

To consider this project successful, we would like to see:

* No safety violations or injuries.

* A tesla coil that produces small visible and audible 3-5cm sparks to our ground rod.

* The coil can play several different notes and tones.

* The coil can take input from the guitar and will play the corresponding notes.

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