With support for 9 piezos + 1 FSR, NiftyDrum packs unmatched versatility into a Raspberry Pi Hat-form factor board. In a nutshell, NiftyDrum is an affordable way to add professional MIDI triggering to your electronic or acoustic drum setup.

Trigger to MIDI Interface

The board

NiftyDrum is a trigger to MIDI interface. It is a sensor to MIDI interface, which means that it doesn’t produce sounds, rather it sends MIDI messages over USB. To convert those messages into sounds, you need a DAW (digital audio workstation).

There are 10 inputs: 9 of which are dedicated to piezoelectric sensors, and 1that is meant to be used for an FSR sensor. Each input is to be connected to a terminal block, and all the piezo inputs have an on-board potentiometer to adjust sensitivity in case the digital gain wouldn’t be sufficient.

The board has the same form-factor as EveryDrum: it can be connected to a Raspberry Pi and follows the Raspberry Pi Hat specifications. The GPIO port is connected to the 5V, GND, and serial output of the on-board microcontroller, so the MIDI notes can be received by a Raspberry Pi without connecting a USB cable to the board.

On the board, there are two LEDs, one of which is on as long as the board is connected via USB or to a Raspberry Pi. The other LED is a status LED, it is almost always on, except when the board is transmitting serial data.

That’s a Blue Pill!

You can write your own firmware and upload it to the board! If that is something you’d like to do, read on! Otherwise, you can skip this section.

The on-board microcontroller is nothing more than the STM32F103C8T6, that’s a Blue Pill! If you are not familiar with the Blue Pill, it is a famous development board based on the STM32F103C family of microcontrollers.

If you want to hack the board and use your own firmware, you can use utilities available at TheKikGen’s repository, as the STM32 has already been flashed with the STM32F10x TKG-HID-BOOTLOADER. To enter bootloader mode and upload a firmware to the board, simply double press the on-board button.

Another way to upload your own firmware to the board is to use the NiftyDrum App.

That gives you a lot of freedom, as you can do whatever you want with the 72MHz, 64kB of flash, and 20kB of RAM that the STM32 gives you.

I have forked Roger Clark’s Arduino STM32 code to provide an easy to program the RonnaTech boards.

Be sure to read the instructions before trying to use.

Just like the actualy Blue Pill, the on-board LED is connected to PC13. The hi-hat controller is connected to PA3, all other analogue inputs are connected piezo inputs from PA0 to PB1.

There is also an on-board EEPROM, it is a M24C64-R, which can hold up to 8192 bytes and is accessible via I²C using the 0x50 address.

MIDI messages

Using the preloaded firmware, each piezo is considered to be a single-zone pad. Inputs are labelled with instrument names to help you wire your kit, but those names are only names, the only exception is the HHC input, which is to be used with the hi-hat controller/pedal.

Piezo inputs are treated as drum triggers. They emit two MIDI messages: note on, and note off. A note on is always followed by a note off after some delay.

The FSR (hi-hat controller) input emits more MIDI messages. It emits note on and note off messages when a foot chick is detected, and control change (CC) messages when the pedal is pressed or released. This allows for continuous monitoring of the pedal state and should allow DAWs to generate realistic hi-hat sounds.

Desktop Application

This section will show how the PC app works. It is a Windows, Mac, and Linux app that allows to control the board’s parameters, such as scan time, mask time, threshold, etc.

Legal notice / Licenses

The firmware is provided as is and can be replaced by any firmware that fits into the microcontroller flash memory, using the on-board bootloader, as described in this post.

Likewise, the bootloader can be replaced by any bootloader that is compatible with the microcontroller, using the J1 connector with a Tag Connect TC2030-NL connector.

Doing so, whether it’s for the firmware or bootloader, may break the microcontroller, so there is no guarantee that the board will still work after such operation. In that case, Ronna Technologies would not be responsible for any issues that you would encounter with the NiftyDrum product as a whole.

If you choose to keep the default bootloader and firmware, here are some things that you need to know:

• The booloader is an unmodified version of STM32F10x TKG-HID-BOOTLOADER. It is published under the GNU GENERAL PUBLIC LICENSE Version 3.
• The firmware, on the other hand, is not open source. It may become open source at some point in the future.
• The firmware uses the following libraries:
  • State Machine Language (SML) library – BSL-1.0 license.
  • SparkFun External EEPROM Arduino Library – The MIT License (MIT).
  • flute: C++20 fixed-point single header library – The MIT License (MIT).
  • JSMN – The MIT License (MIT).
  • libmaple – The MIT License (MIT).
  • USB Composite library for STM32F1 – The MIT License (MIT).

What is EveryDrum?

EveryDrum is a drum trigger signal conditioner interface.
One side of the board is to be connected to piezoelectric sensors. The voltage coming from the sensors is transformed in order to be constrained to the 0-3.3V range. This board was initially designed to be used with an Arduino Nano Every, but other pin-compatible boards can be used.

Because the piezoelectric sensors (piezos) output voltages are constrained to the 0-3.3V range. The intended goal of this board is to make a drum module out of an Arduino, but it can be used for many other applications.

Any board that has the form factor of an Arduino Nano, and is pin-compatible, can be used to digitize piezos voltages.

How to use EveryDrum?

Using EveryDrum is fairly simple, you just have to connect your piezos, and optionally one FSR sensor (HHC) to the 8 terminal blocks. Each sensor is connected to the ground on the left side of its terminal block.

Then, you need an Arduino Nano Every, or a pin-compatible board. Connect it to the board using the two 15-pin headers. USB connector should be on the left side of the board.

It’s now time to install a firmware on your Arduino.

Arduino firmware

The current firmware is still a work in progress, but it is functional and usable as a drum module. It is available from GitHub: https://github.com/SpintroniK/exadrumino-Nano-Every.

Instructions are on the GitHub repository. The firmware sends MIDI over USB, but the MIDI messages are received via a serial port. So this is not a USB MIDI device, rather a serial device that sends MIDI messages over a serial port.

From MIDI messages to sounds

This section will be completed in a near future. But for now, the best option is to use eXaDrums. On Ubuntu, Debian or Raspberry Pi OS, you can install it using the following command line: sudo apt install exadrums.

You can also build eXaDrums yourself using those two repositories: https://github.com/SpintroniK/libeXaDrums and https://github.com/SpintroniK/eXaDrums.

This is a Linux only solution, but there are workarounds for Windows, and probably MacOS too.

Assuming that you have installed eXaDrums, you can go to the “Sensors Config” menu, and select the “SerialMidi” sensor type, and then fill the serial port field. Most of the time the serial port is /dev/ttyACM0, but that depends on your system.

Once that’s done, you can configure each instrument of the current kit by setting their MIDI notes. Start eXaDrums, and play drums!

Making an affordable drum module has been one of my main projects since 2017.
Although making drum modules is not the sole purpose of the company, it is what started it.
So I’ll take a moment to explain how the company came into existence
But before I go into that, I have to explain how a drum module is made.

What’s in a drum module?

Essentially, a drum module converts sensors output voltages into sounds.
For instance, a snare drum contains at least one piezoelectric sensor. When the drum head is hit, this piezoelectric sensor (piezo) converts vibration of the drum head into a voltage. This is the de definition of piezoelectricity: it converts a mechanical stress into an electric charge.

But there’s a catch: the resulting voltage is very high, and goes from negative to positive values.
This is why the first piece of a drum module: a piezo signal conditioner interface.

Piezoelectric signal conditioner

A piezoelectric signal conditioner is an electronic circuit that constrains a piezo’s output voltage to a given range of values.
Most microcontrollers operate from 0V to 3.3V, or 0V to 5V.

There are many ways to make a piezoelectric signal conditioner, but the first stage is always used to scale down the voltage and protect the rest to of the circuit.

The rest usually depends on specifications. Especially regarding the use of a symmetric power supply.
But even if a symmetric power supply is used, at some point the mapped voltage will have to be within the [0, 3.3]V range.

This is what the first product of Ronna Technologies does.
EveryDrum is a drum trigger signal conditioner interface.
The piezos that are connected to the board are connected to an analogue electronic circuit that maps their output voltage to the [0, 3.3]V range.

Analogue to digital converter

Once it’s been scaled to the desired range, the output voltage of a piezo is digitized and processed in order to produce a sound.

In order to digitize the piezo voltage, an Analogue to Digital Converter (ADC) must be used.
It can be an external ADC, or a microcontroller’s integrated ADC.
In both cases, this steps allows processing the signal using various digital signal processing (DSP) algorithms.

Usually, it’s best to get about 10 samples of the piezo’s voltage every millisecond.
That leaves about 0.1 ms between each sample, so the DSP algorithms must be fast enough to process a sample in less than 0.1 ms.

Digital signal processor

Once the piezo’s voltage has been digitized, it can be processed.
At this point, all the electronics is done, it is now a matter of software and DSP algorithms.

Usually, the waveform is processed in order to find a peak velocity.
Depending on which instrument has been hit, a note is chosen, and a volume associated to that note is computed from the velocity.

Sound generator

This last step is optional, if it is ignored we don’t really talk about a drum module any more, but rather a trigger module.
However, if this step is not ignored, things can become tricky.

The goal is to generate sounds from the previously computed notes.
What makes this step tricky is that everything must be done in a few milliseconds, at most.
This is where performance really matters.

Past projects

Before Ronna Techologies, I have worked on a complete drum module: eXaDrums.
It includes all four steps mentioned above, even the sound generator.

eXaDrums

Initially called RaspiDrums, eXaDrums was created in 2015.
My main goal was to make a modern drum module with a touchscreen user interface.

In 2016, eXaDrums was the first drum module offering a touchscreen interface.
It used a Raspberry Pi 3, which was not a very powerful device, but allowed a latency as low as 6ms.

More info about the project here: exadrums.com.

eXaDrumino Nano Every

This project is closely related to eXaDrums, as the name suggests.
It’s also my first real Arduino project.

The goal was to make a drum module using an Arduino Nano Every.
With the Arduino’s ATMega4809, an 8-bit microcontroller running at 16MHz, it was quite a bit of a challenge, but it did work out pretty well.
More info about the project here and here.

For this project to work, I had to make an electronic board that maps the piezos voltages to the [0, 3.3]V interval.
I also had to ditch the Arduino libraries completely and write the firmware in bare C++17, using AVR GCC.

You’ll notice that I have used three of the four ingredients that make a drum module.
To get the fourth ingredient (sound generation), the Arduino needs to be plugged to a PC.
But guess what, exadrums is compatible with this board!

So, at this point, I was confident I could make a complete drum module, including the electronics.
Furthermore, the exadrumino’s performance was very good, given the hardware that I used.
I thought selling the board would make a lot of people’s lives easier.
But the thing is, in France you can’t really do that without creating a company, so I decided to start my own company.

Current projects

To be honest, I didn’t want to start a company to sell a single product.
As stated above, a drum module is made of four parts, so maybe it’s not a bad idea to have a product for the first part.

EveryDrum

EveryDrum is a drum trigger signal conditioner interface. It’s based on the board that I made for exadrumino.
Actually, it’s just an analogue electronic board that maps piezos voltages to the [0, 3.3]V range.
It has two female headers that are compatible with the Arduino Nano Every.
You can use any microcontroller you want, as long as the pinout is compatible with the Arduino Nano Every.

There is also an additional input for a hi-hat controller.
I will share more information about this project in a future post.

Other projects

Of course, I’m working on other projects than EveryDrum.
Right now, there are two projects I’m working on.

The first one is a trigger to MIDI module.
So far, I think it will have at least 12 inputs: 9 triggers, 1 force-sensing resistor (FSR), and a few switches, perhaps 3 or 4 of them.
A bigger version of the board will have more inputs. Probably something like 15 triggers, 1 FSR, and a few switches.

Before we continue, here’s a quick reminder about e-drum sensors:

• Trigger: basically a piezo sensor that “triggers” an event every time its voltage reaches a certain threshold. Used in snare drums, toms, etc.
• FSR: force-sensing resistor. It converts a force into a resistance, which can be converted to a voltage. Used in effect pedals, such as hi-hat controllers.
• Switch: simply a switch. It is open by default, closed if pressure is applied to it. Used in cymbals to determine if they are to be choked.

The other project I’m working on is a development board.
The goal is to have something better than an Arduino Nano Every to use with EveryDrum.
It will be based on a STM32, and have at least 12 inputs.
This is still a work in progress, so I can’t say more about the project right now.

Conclusion

Hopefully, now you know a bit more about Ronna Technologies.
Even though most projects are e-drum related, I’m interested in a lot of other things.
Electronics and programming are my passions, and using those skills to make e-drum products is very rewarding.

I believe that e-drum product are usually way too expensive for what they really are.
A piezoelectric sensor is so cheap, and electronic components are also quite affordable, so why not make e-drums cheaper?
That’s what I’m trying to achieve with Ronna Technologies.
Hopefully, I’ll succeed and make great and affordable e-drum devices.