After following the LDR product development for a few months, when Tortuga Audio announced the upcoming Hi-Z capability of the LDR3x in October, I resolved to build one. Like some other customers, I felt that feedback on volume level and changes were capabilities that I would prefer. Notably, Morten swiftly resolved the latter with the “LED fast blink” feature.
While researching the project, I realized that a compatible volume display could be developed without modifying the LDR3x itself. The LDR3x’s digital control of the attenuation circuit, plus the availability of comprehensive documentation make this possible. So in the spirit of DIY, I decided to “roll my own” display using a separate microcontroller. While it was for my own benefit and purposes, I think it exemplifies the value of Tortuga Audio’s extremely open design philosophy for the LDR3x, demonstrating its capability to be seamlessly integrated into other audio products.
Perhaps an obvious question: would I choose to do it again now that the DM1 is available? Hard to say, but I am certainly happy with the results. With the second micro, I was able to implement benefits to operational feedback that are both logical and assuring. Examples include visual confirmation of button presses, and fading/scrolling for mode transitions.
What follows is a video demonstration, and a brief technical discussion of the implementation for those who are interested. Initially, I wired up an 8x8 LED as the display output, but later realized that the same code could easily drive a high resolution (128x64) OLED. The video shows both displays being run through test procedures.
Video link: http://youtu.be/hpvTTf8rDEI
Like the DM1, the display microcontroller connects using the J4 header, exposing the LDR3x SPI bus and providing access to the IR and encoder pins. With my implementation, the Alps encoder and infrared receiver are captured and interpreted by the display microcontroller, which then relays commands to the LDR3x by emulating the decoded infrared commands on the J4 IR pin. For example, if balance mode is selected via the encoder button, the LDR3x receives an IR as if the balance button was pressed on the remote. The exception is for volume change, which can be transmitted far faster than IR by emulating a quadrature encoder signal on the J4 EA and EB pins.
System state itself is determined through a rule-based model emulating LDR3x behavior and correlating the inputs from the status LED, encoder and IR. LDR3x SPI (internal communications implementing attenuation and balance) activity is monitored to ensure that a command is not accepted by the display microcontroller at a time that the LDR3x cannot process it.
The system configuration is adjustable via the user interface. In the video you may note that the display output can be inverted – the 8x8 LED I originally intended to use had its connector on the wrong side so I just turned the display over. Volume can be depicted either in the standard 0-70 steps, or attenuation dB according to the published scale. I am only planning on wiring up 2 sources, so I added an option to make the source count configurable, such that the LDR3x won’t attempt to switch to a source that doesn’t exist. All the options are stored in EEPROM, and survive a power-cycle.
Overall, designing the volume display was a very educational and fun project pleasantly divergent from amp construction. I learned how to do a lot of interesting things with microcontrollers! One of my recent e-mails to Morten said, “Thank you for creating such a cool product that made me do a cool project.” Such is the nature and essence of the DIY community. I must say that seeing innovative audio technology implemented in such an accessible manner is very unique.
I have a little more work to do on the final PCB and the display mounting on the front panel, and will post some follow-up pics when that is complete. I’m especially looking forward to everything being done so I can listen “non-developmentally” in the near future!
Tim
P.S. Have I mentioned that a volume level display makes the LDR3x much nicer to use? Go and place an order for a DM1!
