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MIDI synthesizer

This is the MIDI synthesizer project for the RISC-V Design Challenge. I'm using this board for it.

The board is configured to receive the MIDI data with an opto-isolator with the standard MIDI frequency of 31,250 Hz. The firmware then detects note-on and note-off events and generates a PWM signal with the requested pitch.

Soldering the MIDI-in board and testing the project:

https://www.youtube.com/watch?v=y-bby_u5XV8

Software

First install MounRiver, as described here: https://www.youtube.com/watch?v=JHzsH9RhTR4

Then download or clone this repository and open the project file midi-synthesizer.wvproj in the midi-synthesizer directory. You can then build and upload it.

Hardware

Circuit diagram of the MIDI-in board: MIDI-in

You can find the KiCad project in the midi-in-module directory. There is also a gerbers.zip file, which you can use to order your board from a PCB manufacturer like https://jlcpcb.com.

Parts list, which you can get from https://www.digikey.com:

Id Designator Package Quantity Designation Digi-Key Part Number
1 D1 SOT-23 1 BAV99 3191-BAV99CT-ND
2 R1,R3,R4 R_1206_3216Metric 3 220 311-220ERCT-ND
3 J3,J2 PinHeader_1x10_P2.54mm_Vertical 2 Conn_01x10_Male Z12462-ND
4 J1 DIN_CUI_SD-50BV 1 DIN-5-GND CP-3150-ND
5 C1 C_0805_2012Metric 1 100n 478-1395-1-ND
6 R2 R_0805_2012Metric 1 2.2k 311-2.20KLRCT-ND
7 U1 DIP-6_W8.89mm_SMDSocket_LongPads 1 H11L1 H11L1SMCT-ND

When soldering it, you can use (this interactive placement tool)[midi-in-module/bom/ibom.html] to find the location of the components.

You can connect the PWM output directly to a high impedance amplifier, or you can build a simple amplifier with a N-channel MOSFET to drive a speaker, as seen in the video:

speaker

Connections

On the dev board, connect PA0 to LED1, to light the LED when a note is playing. Connections to the MIDI-in board:

dev board MIDI-in board
VCC +5V
GND GND
PA10 MIDI-in

Note: VCC is 3.3V. The MIDI-in board works with 5V and 3.3V.

Then connect PA8 to an audio amplifier, connect a MIDI keyboard, or a USB-to-MIDI interface as seen in the video.

Credits

The MIDI demo file is from https://www.free-scores.com/download-sheet-music.php?pdf=11596#.

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MIDI synthesizer for the RISC-V Design Challenge

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