Sunday, 15 May 2016

DMFX-1-1 (main board) schematics and BoM

DMFX-1-1 includes the following blocks:
  • TI C5535 DSP-1 implements the digital effects and audio codec control (pages 2-3)
  • TI AIC3204 ADC/ADC audio codec and buffer, 12MHz clock oscillator, stereo headphones output jack (page 4)
  • DSP-1/2 external memories: SPI, I2C, SD/MMC (page 5)
  • DC/DC step-down switching regulators (3.3V, 1.8V) and LDO (1.3V), power-on reset, clock driver (page 6)
  • FTDI2232 USB/JTAG interface an SEEPROM (page 7)
  • TI C5535 DSP-2 implements LCD, navigator buttons, tuner control (page 8)
  • DMFX-1-2 mezzanine Connectors and footswitch push-button (page 9-10)
  • Line-In stereo input buffer, filters, distortion circuit (page 11)
  • Line-Out dual-mono output buffers and filters, tuner, noise supressor circuits (page 12)
DMFX-1-1: Schematics page 1 - Table of Contents
    DSP-1 implements the digital effects and control the audio codec. It includes a dedicated mini-USB connector. Four analog SAR ADC input are connected to DMFX-1-2 potentiometers. DSP-1 is the first device on the JTAG daisy chain connected to USB/JTAG device to allow JTAG emulation and debugging. INT0 input is connected to DSP-2 external flag (XF) signal and DSP-1 XF signal is connected to DSP-2 INT0; both DSPs exhange interrupts to allow synchronizing processes and tasks between both processors. INT1 is connected to DSP-1 GPIO10. Two SD/MMC cards are connected to DSP-1 to store data, samples, loops, code...
    I2S2 interface is a fast serial interface to exchange samples between DSP-1 and ADC/DAC on audio codec. SPI interface is connected to an external SPI flash to store code and data. UART interface is connected to CBUS on USB/JTAG-UART device and it can be used as console for emulator debugging. I2C bus is connected to external SEEPROM, to store parameters or inventory information. I2C is used for configuring audio codec, and it is also connected to DSP-2 to exchange FX configuration parameters set by user interface via LCD menu and buttons.
    DMFX-1-1: Schematics page 2 - DSP-1 FX interfaces
    Page 2 shows DSP-1 power supply inputs, ferrite filters and decoupling capacitors.
    DMFX-1-1: Schematics page 3 - DSP-FX power

    Page 3 shows TI TLV320AIC3024 audio codec that includes ADC/DAC, LINE input, MIC input, LINE out and stereo headphones amplifier. I2S is a high speed serial interfaces to echange audio samples with DSP-1 at a sampling frequency configured by DSP-1. Interface is buffered via a CBTLV3245 octal bus switch. 12MHz clock oscillator is included here, it is connected to a clock driver on page 6.
    DMFX-1-1: Schematics page 4 - Audio CODEC ADC/DAC
    Page 5 includes two W25Q64 64-Mbit SPI flashes connected to each DSP SPI interface. Two SD/MMC cards are connected to DSP-1 for large storage (samples, loop, data). One I2C 64Kbit SEEPROM 24C64 can be used to store remote inventory or configuration data.
    DMFX-1-1: Schematics page 5 - Memories I2C, SPI, MMC
    Page 6 shows two DC/DC step-down switching regulators TI TPS56220. They generate +3.3V and +1.8V respectively from a +9V external supply or +5V USB input with a maximum current of 500mA each. A TI TPS73201 LDO generates the analog 1.3V DSP supply voltage from 1.8V input at a maximum current of 250 mA. A TI CDCLVC1108 octal clock buffer generates up to 8 clocks from 12MHz clock oscillator: USB DSP-1 clock, DSP-1 system clock, audio codec master clock, USB/JTAG clock, USB DSP-2 clock and DSP-2 system clock.
    DMFX-1-1: Schematics page 6 - power supply, clock driver
    Page 7 shows an FTDI2232 USB/JTAG interface device that works as XDS100v2 TI emulator for DSP debugging. ABUS is connected to JTAG daisy chain on DSP-1 and DSP-2. CBUS is sonnected to UART interface on DSP-1. A D-type flip-flop detects power reset rising edge from FTDI device and generates a power detect signal back to the FTDI device. An external SPI SEEPROM AT93C46 stores USB device configuration parameters. USB port is protected for ESD. USB debug port is a type-B USB connector. The +5V USB debug port can be used to power the whole DMFX-1 system. DMFX-1 system can actually be powered from any of the three USB ports or by an external +9V power supply.
    DMFX-1-1: Schematics page 7 - USB/JTAG
    DSP-2 implements user interface and control tasks. It includes a dedicated mini-USB connector. Two analog SAR ADC inputs (AIN0-1) are connected to tuner circuit output and noise supression circuit output respectively, AIN2-3 are connected to DMFX-1-2 potentiometers 2-3. DSP-2 is the second device on the JTAG daisy chain connected to USB/JTAG device to allow JTAG emulation and debugging. INT0 input is connected to DSP-1 external flag (XF) signal and DSP-2 XF signal is connected to DSP-1 INT0; both DSPs exchange interrupts to allow synchronizing processes and tasks between both processors. INT1 is connected to DSP-2 GPIO10.
    DSP-2 GPIO0 controls clean or distorion audio input to audio codec. GPIO1-2 configure the overdrive/distortion gain, GPIO3-4 control different overdrive/distortion modes, increasing mid tones or setting fuzz clipping diodes circuit. GPIO6-11 drive five red LEDs on DMFX-1-2 mezzanine board. GPIO11 is connected to CPU active green LED.
    SPI interface is connected to SPI flash (device 0) and to 128x32 graphic LCD (device 1) on DMFX-1-2 mezzanine board, GPIO12 is connected to LCD A0 signal and is used to send command or data to LCD via SPI bus. GPIO13-17 are connected to the five navigator buttons respectively: left, up, center, down, right.
    GPIO28 is connected to footswitch.
    SPI and UART interfaces are not used. I2C bus is connected to DSP-1 to exchange FX configuration parameters set by user interface via LCD menu and buttons.
    DMFX-1-1: Schematics page 8 - DSP-2 Control interfaces
    Page 9 shows DSP-2 power supply inputs, ferrite filters and decoupling capacitors.
    DMFX-1-1: Schematics page 9 - DSP-2 Control Power
    Page 10 shows DMFX-1-2 mezzanine connectors. J5 connector includes DSP-2 SPI2 bus, LCD A0 addess signal, reset signal and the five navigator button inputs: left, up, center, down, right. J7 connector includes LED1-5, DSP-1 GPAIN0-3 SAR ADC signals, DSP-2 GPAIN2-3 SAR ADC signals, distortion circuit output, octave circuit output and the mix of distortion-octave coming from a potentiometer on DMFX-1-2. +3.3V, analog +1.3V power supplies and ground.
    DMFX-1-1: Schematics page 10 - Connectors
    Input buffers and filters and distortion circuits are based on TI rail-to-rail LME49721 audio op-amps powered at +3.3V, in contrast with +9V supply normally used on guitar pedals. 

    Overdrive/Distortion:

    First opamp stage has 0dB gain but implements some low pass filtering. Second op-amp stage implements a configurable gain controlled by DSP-2 GPIO signals connected to OD_DRV0-1. when both switches are active (shorted) we obtain the minium gain value of 13dB (x4.5), if OD-DRV1 is open, gain value is incremented by 10dB (x14.5), if OD_DRV0 is open, gain value is incremented by 9dB (x40). Third op-amp stage implements high saturating gain (hard clipping) or soft clipping via asymmetric diodes, when OD_MODE1 is 0, a 20dB gain is implemented with 10K switch shorted and switch in series with diodes open. When OD_MODE0 is 1, a 10dB gain is implemented, but soft asymmetric clipping is added with Schottky diodes added in parallel to the opamp feedback path.

    OD_MOD0 activates a notch filter that attenuates middle tones by 12dB at 400Hz.

    These four GPIOs: OD_DRV0-1 and OD_MODE0-1 allow different combinations of gain, hard clipping, soft clipping, and mids attenuation to get different types of analog overdrive and distortion effects.

    Octave-up:

    A forth op-amp implements a full-wave rectification that generates a octave up, that can be mixed with distortion output.

    Line-In circuit:

    The input from a guitar can be connected to Line-In input. The first stage is a J-FET buffer, followed by a filter that boosts up to 6dB high frequencies and attenuates down to 9dB low frequencies. 0dB occurs at 3.7kHz. The filtered line-in signal is the input to the tuner circuit and to an analog switch that can select the clean or the distortion at its output. The output of the switch is connected to the Audio Codec analog left channel input. Right channel input is connected to the clean signal, this allows mixing clean and distorted signal within DSP and obtain a more or less overdriven signal.
    The op-amp at the bottom of the page is a follower buffer that generates a middle point reference signal at 1.65V equal to 3.3V/2. Op-amps are rail-to-rail TI LME49721 powered at 3.3V.
    DMFX-1-1: Schematics page 11 - Input buffers, filters, clean, distortion
    Page 12 shows right and left channel pre-amp circuit with high impedance Line-Out signals that can be connected to a guitar amplifier or Line-In input of a sound card or sound equipment.This pre-amp amplifies 9dB with a 3dB bandwidth of 1.35kHz, 0dB is at 4kHz. The first op-amp stage filter is a low pass filter with a pole at approximately 14kHz and 3dB bandwisth at 24 kHz.

    The two op-amp circuit at the bottom of the page is used as support to the tuning and noise suppression circuit within the control DSP-2. The first stage is a very high gain amplifier that can be used as power detector for a noise suppression algorithm. The second op-amp is used as comparator and generates a square wave between 0 and full scale with the same fundamental frequency as the input signal and zero voltage when no signal is present. This square wave simplifies tuning algorithm using and auto-correlation method. Both tuner and noise suppression signals are connected to analog inputs of SAR ADC circuits within the Control DSP-2
    DMFX-1-1: Schematics page 12 - Output buffers, filters, tuner, noise suppression

    Schematics and BoM source files

    Schematics and layout have been made using CAD Eagle 6.3.0. Source files can be found in the DMFX-1-1 github HW repository including Eagle Schematics source files (.sch), Eagle Board layout files (.brd), Eagle component libraries (.lbr), Schematics in pdf format, and all manufacturing files including gerber files, assembly drawings and pick and place files. An Excel file contains the full BoM including reference designators, manufacturer part number  as well as Digikey part number.

    For your convenience here is a link to DigiKey with a BoM of the whole DMFX-1 platform including main board DMFX-1-1, described in this post, and the daughter board (DMFX-1-2 with LCD and navigator buttons). You'd better verify BoM completion, lead-times and obsolescent components beforehand.

    With all this information you can build your own DMFX-1 platform and develop your own Digital effects!!

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