Building a Low-Power E-Ink Calendar Display with ESP32 and HomeAssistant

GreatScott!

Dashboard Replacement Justification [0:00]

The presenter initially had a Smart Home Dashboard (Image 0) which he and his girlfriend found became an "eye sore" due to underuse, as they primarily used the HomeAssistant App on their phones (Image 4).

• Limitations of the old setup:
  • The old LCD, touchscreen, and Raspberry Pi combo was overkill for just a calendar display.
  • It consumed too much power, up to 10W, which was inefficient for its limited utility.
• Motivation for a new solution:
  • They wanted a useful replacement for the old screen that could display their shared online calendar events.
  • An E-Ink display was identified as an ideal alternative due to its low power consumption and ability to retain screen information without power.

E-Ink Display Selection and Testing [1:53]

The presenter opted for an E-Ink display to resolve the power and utility issues of the old dashboard.

• Advantages of E-Ink displays:
  • Retains screen information when not powered, meaning it only consumes power during refreshes (Image 29).
  • Draws almost no current when static.
• Display specifications:
  • A 13.3-inch E-Ink display was chosen to cover the existing hole and wall anchors from the previous dashboard setup.
  • The display was acquired with an ESP32 development board (Image 41).
• Initial testing:
  • Example code was uploaded to the ESP32 board.
  • The E-Ink display was hooked up and powered, confirming functionality and acceptable display quality for a calendar (Image 45).

Software Architecture and Setup [3:50]

The project utilizes Google Calendar, HomeAssistant, and an ESP32 for event management and display.

• Google Calendar integration:
  • Google Calendar was chosen for its easy sharing features and accessible free API for event data.
• System architecture:
  • Instead of the ESP32 handling all data processing, HomeAssistant acts as an intermediary (Image 56).
  • HomeAssistant fetches calendar data from the Google API, then processes and sends it to the ESP32 via MQTT.
  • This approach allows for calendar management within HomeAssistant and potential future automations.
• HomeAssistant setup steps:
  • Enabled Google Calendar API service and integrated it into HomeAssistant using an existing guide (Image 63).
  • Created an "eink_calendar_sensor" in configuration.yaml to grab calendar events (Image 66).
  • Verified the sensor successfully retrieved event attributes (Image 68).
  • Created an automation to convert the sensor data into JSON format and publish it to an MQTT topic (Image 70, Image 71).

ESP32 E-Ink Calendar Code [5:58]

The ESP32 was programmed to receive, process, and display calendar data efficiently.

• Library selection:
  • A community-written Arduino library, GxEPD2, was chosen over the manufacturer's library for better support and popularity (Image 73).
  • A "HelloWorld" example was successfully tested (Image 75).
• Over-The-Air (OTA) updates:
  • The ElegantOTA library was implemented to allow for wireless code uploads via a web server interface, eliminating the need for physical connection (Image 79).
• MQTT integration:
  • Code was added to enable the ESP32 to subscribe to the MQTT topic and receive JSON event data from HomeAssistant (Image 81, Image 82).
• Calendar rendering logic:
  • The most complex part was sorting events, assigning them to days, and displaying them.
  • The goal was a 7-day agenda, always starting with "Today" and "Tomorrow," followed by the remaining weekdays (Image 86).
  • This required the ESP32 to grab the current time and date (Image 88), perform additional sorting, and format the output aesthetically (Image 89).
  • Further refinement included integrating time sorting, with earlier events at the top and later events at the bottom (Image 92).

Electrical Wiring [7:50]

The power setup was designed for efficiency and convenience.

• Power consumption:
  • The entire system, when active, requires approximately 0.3W, with peak current flow just above 100mA (Image 97, Image 98).
• Power supply:
  • A small 5V power supply was used (Image 99).
  • The power supply was wired to mains voltage (Image 100).
• Remote control:
  • A Shelly Mini smart relay was integrated into the wiring to allow the system to be turned on and off remotely via HomeAssistant (Image 102).

Custom Enclosure Design and 3D Printing [8:38]

A custom enclosure was designed and 3D printed to house the E-Ink display and electronics.

• Design process:
  • Mechanical drawings of the display were used to create prototype designs.
  • The design was refined through several iterations, eventually resulting in three interlocking parts (Image 109).
• 3D printing:
  • The final parts were printed using white PETG filament.

Final Assembly and Verdict [9:56]

The components were assembled into the 3D-printed enclosure, and the calendar was mounted.

• Assembly steps:
  • The E-Ink display was seated into its indentation.
  • A holder piece secured the display with screws (Image 122).
  • The ESP32 board was reattached, requiring direct soldering to the 5V and GND pins for power due to USB cable clearance issues (Image 125).
  • The ESP32 was secured with hot glue.
  • The mains power supply and Shelly Mini were connected to the wall.
  • The entire display unit was mounted using existing wall anchors and screws.
• Successful outcome:
  • The E-Ink calendar was successfully completed and installed (Image 130).
  • The presenter expressed satisfaction with the result, noting its improved utility and aesthetic appeal.