2 Way Version

The Hardware:

• MCU: Micro Controller Unit.

Arduino DUE is the only choice available at the moment. The software for ESP32 has not been developed Yet. The problem of this 2-ways version is that it uses a VGA display to output the GUI. A VGA monitor minimum size is usually 7'' from all manufacturers. So the only problem is actually the size on the panel that force us to use a minimum case size of 3U 19'' Rack (With a front panel height of around 10'' or 12-13cm. The metal frame mounted VGA monitor I choose in my prototype is 121mm high and it has a mounting rectangular hole of 108mm for the height and 150mm for the width.

ESP32 in future will allow the possibility to use the crossover through his Android App, using your favorite Android device or a dedicated WiFi tablet. But anyway not necessarily using so much space on the front panel. The downside of the ESP32 version is the fact that this configuration will have a relatively small latency controlling the crossover from the App remotely, because it needs to send data trough WiFi or Bluetooth and receive back a data feedback from the machine to can actually see your parameter changes on the display of your Android device.

• MBoard: Connections Arduino DUE shield.

The connections shield is a small board carrying all the circuitry necessary to connect Arduino to the various peripherals. Shields are boards that can be plugged on top of the Arduino PCB extending its capabilities. The connections shield features a full passive VGA "video card" that allows to control the VGA display in 320x240 pixels resolution with 8-bit color depth. The board it self can be useful for other projects as well.

• FBoard: Filter Boards.

The filter boards needed are just 2. One for left and one for right. This configuration still give use the possibility to have 32 steps of frequency cuts adjustments, 4 different geometries (Resonance levels), selectable order, 12db/oct. or 24db/oct.

• VBoard: Volume Board (Optional).

The volume board can be used as a passive attenuator, or as an active volume control. One board will take care of the output of 4 mono channels, so just one board will be needed for the 2 way version. From every channel (HP-Left , HP-Right, LP-Left, LP-Right) the signal will flow in a 16 steps volume control. The steps can be configured at the building time with different step sizes, for example 0.1db, 0,5db, 1db, etc.

• SBoard: Output selector board (Omitted).

No selector board is needed for the 2-way configuration.

• DPSU and SPSU: Power Supply.

One of the main goals of the power supply of an audio crossover, from my point of view is to keep the ground silent, preventing ground loops, and providing a good separation from the digital grounds to the analog grounds, keeping in mind that VGA signal also carry the ground, and VGA monitors are quite famous to be source of noise in audio signals. I recommend to always use linear power supplies is every single part of the project. I tried the switching power supply that came with the VGA display. When I turned on the crossover there was a huge 50Hz disturbance and the noise level was just so high that I had fear to damage the woofers!!! Replacing the power supply with a normal linear home-made unit the noise level went down at very low levels like should be. The DC voltages needed for the crossover are the following: a high quality +15V/-15V for the analog part of the circuit, usually a 0-12V to supply power to the display, 0-7V to 0-9V for the Arduino DUE, 0-5V for the MCP23017 that in the 2-way version you can get from the Arduino DUE 5V pins without problems, 0-5V to 0-6V to supply power to the relays. For the 2-Way version ULN2803A can be used as relay driver instead ULN2804A to allow latched relays to works with just 5 Volts. For best performances I recommend to use a minimum of 2 transformers (better toroidal ones): the first will be dedicated to the analog part and a small 20VA with 2X12VAC outputs should just be good enough. For the digital part also economical buck converters can be helpful to step down efficiently our voltage from a bigger transformer, but always using after that a good filter bank and linear regulators to avoid switching noise to get in our audio path. Several strategies can be used to avoid to have 3 independent transformers. For example having a transformers with 6VAC and 12VAC secondaries will make your building a lot easier. You can consider also to add by hand a 6V secondary coil to a normal 12V toroidal using enameled 1mm copper wire (we are talking of about 30 - 60 turns depending from the toroidal used.)

The Software:

The Software will be the same for all Arduino DUE versions (2-3-4-n ways). If you have some experiences with Arduino, compile the software on your Win/Linux/Mac computer and flashing it on the Arduino DUE using USB will be pretty easy and doesn't need any external programmer. All the software needed is free and open-source. I will provide a .zip file containing all the libraries included in the software and there will be a software switch to select the maximum ways of your crossover at the software build time. The software will provide the same functions for all versions (2-3-4-n ways). A function I would like to add for the 2 way version is a "All in one page" parameters interface. I'm valuating the possibility to provide also preinstalled Arduino DUE boards.

3 Way Version

The Hardware:

• Coming Soon!

The Software:

• Coming Soon!