The LCDuino-1 display I/O processor


  • May 21, 2011: LCDuino-1 v1.01 boards are now available at AMB audio shop.


LCDuino-1™ is a microcontroller platform designed for advanced audio system status display, control and monitoring applications. Currently, it supports the δ1 relay-based stepped attenuator and δ2 relay-based input/ouput selector with the Volu-Master firmware, and the γ3 high resolution DAC with with the γ3 firmware. LCDuino-1 has the following features:

LCDuino-1 hardware Volu-Master and γ3 firmware
  • Arduino-compatible
  • ATmega328P-PU MCU running at 16MHz
  • "Backpack" board: Plug-in for an industry-standard 2x16 LCD charater display module
  • LCD display contrast adjustment
  • I²C serial control interface to volume control, input/output selector, DAC functions, and other "application modules" (see below)
  • Infrared receiver for wireless remote control
  • Front panel pushbutton switch for power on/off, volume mute and system setup
  • Solid-state relay trigger for system power on/off control
  • Motorized potentiometer driver
  • Real-time clock with quartz crystal for time display (Volu-Master firmware only)
  • Supercapacitor for time-keeping during power-loss (Volu-Master firmware only)
  • LED indicators for power and activity
  • MCU Reset pushbutton
  • FTDI TTL-232R USB cable interface for firmware updates
  • All through-hole parts for ease of assembly
  • Four-layer board with ground plane and power plane
  • Compact board size for easy installation
An assembled LCDuino-1 board, mated to the display module as a "backpack" (click image to enlarge):

  • Two firmware packages available:
    • Volu-Master: For the δ1 attenuator and δ2 I/O selector system
    • γ3: For the γ3 high resolution DAC
  • Common features:
    • "Learn IR": Adaptable to wide selection of remote controls
    • Remote control of all features
    • Up to 256 steps of volume control
    • Fine and coarse (user-settable dB steps) remote control of volume
    • Front panel potentiometer control of volume and menu functions
    • Auto-synchronization of volume knob position (via motorized potentiometer) when changing volume with remote control
    • Volume setting display (bargraph and dB readout, switchable large font mode)
    • Volume control range limits (user-settable)
    • Volume setting stored and recalled on a per-input basis
    • Start-up banners (user-customizable text)
    • Input port name display (user-customizable)
    • LCD backlight off/on/auto modes (user-settable brightness)
  • Features specific to Volu-Master:
    • Build-time configurable 0.1dB, 0.5dB or 1.0dB volume control steps
    • Up to 8 total stereo input and output ports
    • Output port name display (user-customizable)
    • Real-time clock display
    • Switchable single-output or multi-output modes
    • Sleep function (auto-shutoff with user-settable delay)
    • Turn-on muting delay (user-settable interval)
    • Configurable I²C addresses for δ1 and δ2 modules
  • Features specific to γ3:
    • Run-time configurable 0.5dB or 1.0dB volume control steps from 0dB to -127.5dB
    • 5 digital inputs, including USB
    • Input sample rate display
    • Five selectable filters, including linear phase, minimum phase, brick wall, soft-knee, and apodizing types
    • Selectable anti-clipping mode (-2dB attenuation)
    • Upsampling control: 192KHz or 96KHz
    • Digital output control: upsample or loop-out
    • Absolute phase control: normal or invert
    • De-emphasis control: auto or off
    • USB audio class selection: UAC1 or UAC2

Application Modules

The LCDuino-1 board is the core controller with an LCD display, but most of the actual work is done in separate "application modules" connected via the I²C bus and direct I/O pins. The division of labor makes the system very flexible and extensible. The following is a list of currently supported application modules, with more being considered for the future. Please refer to each module's website for more details.

With Volu-Master firmware:
    • The δ1 ("delta 1"):
A precision, highly-configurable relay-based stereo volume attenuator with up to 256 steps.
    • The δ2 ("delta 2"):
A sophisticated, highly-configurable relay-based input and output selector for up to 8 stereo ports.
With γ3 firmware:
    • The γ3 ("gamma 3"):
A high-end, full-featured, high resolution fully-differential DAC.

LCDuino-1 with δ1, δ2 and Volu-Master firmware

LCDuino-1 with δ1 and δ2 provide an elegant, functional, and high performance solution for stereo pre-amplifiers, integrated amplifiers, headphone amplifiers, and other audio components. Each of these application modules are configurable to suit a variety of control needs.

Traditional panel-mount volume controls and selector switches require wire runs from rear-panel input jacks to the front panel, then from there to the amplification circuitry. If the amplifier has multiple switchable outputs, then the signal is routed again to the front panel before going back to the rear panel to the output jacks. The long wiring not only makes the amplifier interior untidy and more difficult to service, it gives rise to crosstalk between stereo channels, crosstalk between inputs, crosstalk between outputs, noise interference, not to mention added cable capacitance and inductance. All of these adversely affect the audio signals passing through.

In contrast, the LCDuino-1 system paradigm not only provides the convenience of wireless remote control and a clean and simple front panel, it physically decouples the application module functionalities from the front panel, allowing a more optimized interior layout. For example, the δ1 volume control and δ2 input/output selector boards can be placed close to the rear panel jacks, minimizing the wiring.

The α10 stereo pre-amplifier, featuring the LCDuino-1, δ1 and δ2, exemplifies the LCDuino-1 system paradigm where the front panel contains a central display and the most essential controls, while the wireless remote control provides access to full functionality. Each module in the pre-amplifier are situated for best performance and without any long wire runs.

AMB α10 pre-amplifier featuring the LCDuino-1, δ1 and δ2 (click image to enlarge)

LCDuino-1 with γ3 DAC and γ3 firmware

LCDuino-1 is a core component of the γ3 DAC and provides all user interface and device control capabilities. As with the δ1 and δ2 system, the front panel contains a central display and the most essential controls, while the wireless remote control provides access to full functionality. The clean and simple front panel belies the many features and capabilities within the unit.

The LCDuino-1 processor communicates with and controls major subsystems within the γ3 DAC, including the γ24 DAC core module, ζ1 Audio Widget USB-I²S module, and other functions on the γ3 DAC backplane board.

AMB γ3 high resolution DAC featuring LCDuino-1 (click image to enlarge)

AMB applications

LCDuino-1 is easy to build and set up, but due to many possible configurations and options, please be sure to read every section of this site (and each application module's websites) carefully before attempting to build it. If you don't thoroughly understand everything, ask questions in the AMB DIY audio forum, or consider having someone more experienced to build it for you.

AMB audio shop offers blank LCDuino-1 and application module printed circuit boards and some related parts (including pre-flashed ATmega328P-PU MCU chips with the bootloader and our Volu-Master or γ3 firmware for "plug and play" use). No Arduino programming knowledge is needed when using the pre-flashed MCU. Other parts are available from online vendors. See the Parts list section.

The LCDuino-1 system and Volu-Master firmware are developed by AMB and LinuxWorks. The γ3 firmware is developed by AMB based on a heavily-modified Volu-Master base. See the History section for details. We believe the functionality, features, performance and polish raises the bar of quality amongst other DIY designs of its type.

Generic applications

Most LCDuino-1 on-board features (i.e., the real-time clock, motor driver, I²C port expander, and LCD display module) are optional. When they are not populated, the board becomes a "generic" Arduino-compatible processor platform, and can be adapted to a wide range of uses. Virtually all of the MCU's analog and digital I/O lines have dedicated and labeled wire pads for easy connection to external devices. You can program it just like the official Arduino board, using the available rich set of software tools, libraries and integrated development environment (IDE).

Arduino programming tutorials are available elsewhere and beyond the scope of this site. The rest of the documentation here assumes that you will be using LCDuino-1 with Volu-Master or γ3 firmware.

The scope of the LCDuino-1 project

The LCDuino-1 system is primarily centered around the LCDuino-1 display I/O processor board, a compatible LCD display module (see the Parts list for details), and the application modules mentioned above. To build a working LCDuino-1 system, you will also need a "constantly-on" 5V DC power supply. The minimum DC current rating of the power supply depends on the number and type of application modules installed.

In a system with one δ1 and one δ2 board, a regulated power supply capable of 300mA output, with peaks of up to 1A is recommended. This system normally does not consume very much current, but the power supply needs to have sufficient current capacity to allow the latching relays on the δ1 and δ2 boards to switch reliably while running the potentiometer motor. Most installations could use the σ25 regulated power supply with an appropriate power transformer. Please see the α10 pre-amplifier and its companion σ10 power supply implementation for reference.

For a γ3 system, I also recommend a regulated power supply capable of at least 300mA output. The average current draw on this supply is higher than on the δ1/δ2 system, but it does not vary as much because there are no relays to drive. The σ25 regulated power supply could be used, but a larger-than-stock heatsink is recommended. AMB recommends the use of the σ11 regulated power supply instead, which has two MOSFETs to share the heat load and provide superior performance. See the γ3 high resolution DAC and AMB's reference power supply implementation for details.

WARNING: Building the power supply for the LCDuino-1 system would require that you work with AC line voltage, which is a lethal shock hazard. If you don't know what you're doing, please ask someone who is experienced to help you. In many cases you could use a 5V DC regulated wallwart power adapter (with sufficient current rating), which lets you avoid working directly with AC mains.

What skills and tools are needed

You should know how to read a schematic diagram and correlate it to the circuit board layout, identify electronic parts and their pin-outs, have decent soldering skill, and be proficient with a multimeter. You need at least a basic set of tools for electronics work, such as a good soldering iron and accessories, screw drivers, needle nose plier, diagonal wire cutter, etc. For the chassis case, you will also need to be familiar with using the tools that are necessary, such as an electric drill, bits, center punch and others.

Why not offer a full kit

AMB is not prepared to stock all the needed parts and offer them as a full kit. This system also provides a number of customizable options that makes it unwieldy for such a kit. Lastly, this system is AMB's contribution to the DIY community rather than a for-profit product, AMB cannot assume the commercial support role that might be implicit with a full kit.

Why not offer completed systems

This is intended to be a project for DIYers, and AMB is not set up to manufacture completed systems, especially in light of the large number of possible configurations and options.

Where to get help

Be sure you read all the information at this site. If you cannot find an answer to a question, or encounter a problem you cannot solve, the best place to get support is the AMB DIY audio forum. Search the forum for an answer before asking a question. Your question may have already been asked and answered.

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