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• Architecture Options

  Andy Geppert • 09/18/2024 at 14:06 • 4 comments

  After a wide survey of options, I think there are two architectures that standout for this project. The first one meets the MUST HAVE requirements and the second one exceeds the NICE TO HAVE requirements with significant benefits and capabilities. I welcome feedback and discussion on this fork in the road!
  

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  ARCHITECTURE V1 (OLED with I2C simplicity):

  • Display is OLED with I2C control directly via SAO I2C lines.
  • The two knobs are analog pots, each connected to GPIO 1 and 2 of the SAO port.
  • Accelerometer is connected to the SAO I2C lines.

  Architecture V1 is the easiest and most direct path to a solution. But it lacks the ePaper, which I think is the magical element that will really make the Etch sAo Sketch pop. OLEDs are nice, but I think people will enjoy ePaper more. This will be my starting point. Maybe using a fully illuminated OLED display, with the drawing point being OFF pixels will sell the look?
  

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  ARCHITECTURE V2 (ePaper, I2C-to-SPI bridging, standalone MCU operation, with even more benefits):

  • Display is ePaper, which is only available with a SPI interface. Minimal [enough] SPI functionality could be bit-banged through the 4 available SAO lines, but this deviates from the I2C bus standard expected with SAOs. Therefore, I2C to SPI translation is needed. A dedicated solution exists as an NXP SC18IS606 I2C to SPI Bridge, about $3 in low volumes. But a DIY MCU bridge could easily cost less. See MCU point further down...
  • The two knobs are still analog pots, optionally connected to SAO GPIO1&2, or tied to the MCU onboard the SAO, enabling stand-alone operation.
  • Accelerometer is still connected to SAO I2C lines, and optionally accessible by the onboard MCU.
  • The MCU. I could roll my own dedicated bridge on a low cost MCU like this, but I'd like to pick up a lot more functionality by using a small pre-made MCU board. Considering capability, compatibility, support, ubiquity, price, a desire for USB-C to Arduino simplicity... leads me to the RP2040-Zero and ESP32-C3. Both of those are available for < $2. I really like the drag-n-drop simplicity for firmware on the RP2040 (no IDE needed), but I also like that the ESP32-C3 opens the door for this SAO to access Wifi and BT. Perhaps I can configure the footprint on the back of the SAO to work with either board. Otherwise, it's likely the RP2040 simplicity is going to end up in this architecture.
  • I2C to SPI Bridge: I can do the direct ePaper/SPI heavy-lifting in the ESP, and offer a simplified (and customizable) protocol to the SAO port in either I2C or UART (UART per the SAO standard). And maybe this DIY I2C-SPI bridge could be a spin-off project library to benefit the SAO community and beyond.
  • Having a configurable I2C to SPI Bridge in an MCU also opens the door to other SPI displays, like multi-color OLED and TFT options. This I2C constraint really only exists in the SAO port right now, so not sure that's a big seller. Although, Badge Life and SAOs would benefit more. Considering the whole impetus of this project and the Supercon Add On contest is to stretch into more I2C functionality, why not open the door to SPI too?!
  • Does this mean the SAO becomes the badge?

  Architecture V2 is going to be my extra credit project.

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  Can I complete both by October 15?

• Requirements

  Andy Geppert • 09/18/2024 at 13:39 • 0 comments

  Must have:

  • Display
  • Two knobs
  • Accelerometer
  • SAO connector and I2C control
  • A single 2-layer PCBA with maximum size W 40mm x H 50mm
  • Completed by Supercon 8 SAO contest deadline Oct 15.

  Nice to have:

  • A button (could be used to clear the screen without accelerometer, maybe change modes)
  • Optional standalone mode, operating from only 3V3 SAO power, including an MCU.
    • Accessible, supported, and easy to use MCU with a USB cable and Arduino IDE
  • Display using ePaper, although OLED is directly I2C compatible.

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