The purpose of the Signal Input board component is to aggregate the input signal that comes in from the drum pads via audio cables, digitalise and serialize it, and forward it to the Signal Processing unit.

The input board contains a microcontroller that performs the work.

Concept

The Input Board connects drum pads to the Signal Processin unit. It translates the analogue signal produced by the piezos in the drum pads into a digital signal.

The board is to be designed so that it enables easy extensibility. Considering that microcontrollers are normally limited in the number of analog inputs they provide, each Input Board would be able to control only a limited number of input pads. So, in order to support a larger number of drum pads, several Input Boards would need to work in parallel and all seamlessly connect to the Signal Processing unit.

Inputs

Electronic drum pads are connected via audio cable connectors, stereo or mono.

Various types of pads, from various manufacturers, will need to be supported. As these are mostly piezo elements, some tweaking of configuration should be possible. However, the best place for this purpose is in the Signal Processing unit.

Processing

The analog electrical audio signal is digitalized (serialized) and sent for processing via output. This is as simple as measuring the velocity of the hit, and translating into a digital information, which is sent to the digital output channel.

Outputs

Signal can be sent out via USB port. USB offers a broad bandwidth for communication and should support multiple Input Boards on the bus.

Issues

Issues to resolve:

• support for various types of inputs/pads: hi-hat, toms, cymbals, snare;
• support for piezo/piezo and piezo/switch pads;
• support for various brands' implementation of the same pad, i.e. cymbals from Roland vs Yamaha;
• support for different hi-hat variable controllers, i.e. hall, resistor-based;
• support for multi-zone pads (like Yamaha 4-zone snare);

Hardware

These are the components required. See more details on electric components and Hardware pages.

• Patch panel for TRS connectors.
• Processing board. Normally a microcontroller board or an SoC system.

Solutions

Separate input boards might be necessary in order to support various types of sensors. These input boards should support integration of multiple boards into one compact unit which would be similar to a typical drum module in that it supports all the typical drumset pads (hi-hat, bass, toms, snare, cymbals). This could be done either via a controller board that communicates via digital pins in a star topology, perhaps utilising multiplexers to expand the number of inputs, or in some different manner, using serial or parallel connection between inputs.

There would be at least two separate input circuits:

• variable hi-hat controller (reader for resistor- or hall-based hi-hats)
• drum/cymbal pads
  • piezo/piezo pads
  • piezo/switch pads
• 3-zone cymbal pads

Implementation

• The Arduino-based implementation seemed like the best option to create a prototype.
• Nucleo-based implementation is in preparation.

Grove component option

The input connectors could be implemented as Grove components, allowing simple connection to a board. Basically, providing a Grove connector to the audio jack. This would connect to either the main board or the Grove expansion card/shield.

In this manner, the number inputs would be adjustable and an increase of number of inputs would include adding expansion boards.

Resources

• Building My Own Module thread at vdrums forum (link); rectifier (link)

This is the scheme for the eDrum input component.