inki is a bare-metal, battery-powered, energy-efficient system for ePaper-based display of information gathered via Wi-Fi with a runtime up to years. This repository includes two use cases: room signage as front-end for the SeatSurfing desk sharing system and display of live information from home automation with homematic and ccu-historian. It features a webinterface for setup, a realtime clock-based power control for battery-powered, low-power consumption and wireless operation, an 3D-printed case with dovetail mount, a custom PCB and an ePaper display that retains its content when powered off. See also https://hackaday.io/project/203726-inki-low-power-wireless-epaper-device
Fully assembled 4.2" inki (powered-off) with ePaper display and 3D-printed enclosure.
inki 4.2" operating: realtime clock switching on the device (LED on), pico connects to WIFI and gatheres current booking of desk (originally, desk is free), epaper is refreshes with the new information, device is switching off (LED off).
7.5" version displaying temperature reading of a sensor from the ccu-historian home automation system over the last 24 hours.
If you have a Pico W at hand, you can quickly test:
- Download a prebuilt UF2 from the latest Release:
- Historian: inki_historian.uf2
- SeatSurfing: inki_seatsurfing.uf2
- Homematic: inki_homematic.uf2
- Hold BOOTSEL while plugging in the Pico W → the RPI-RP2 drive appears
- Copy the UF2 to the drive → the board reboots automatically
- The Pico W onboard LED blinks “inki” in Morse
- Connect to the Wi‑Fi AP
inki-setup, then openhttp://192.168.4.1in your browser - Works on a bare Pico W (EPAPER_NONE by default)
inki can be configured and updated with a new firmware via the Wi-Fi setup mode:
-
Start and connect to the inki Wi-Fi hotspot "inki-setup", open your browser and go to http://192.168.4.1.
-
Setup the configuration of the device (settings will be stored for future use)
- Wi-Fi credentials
- Seatsurfing settings, via seatsurfing's Rest API, (copy&paste from seatsurfing "service account": credentials, location id, space id, ...)
- Device settings (room numbers, seats per room, automatic refresh intervals...)
- Optionally upload a custom logo / piktogram
- Optionally upload firmware updates, inki will automatically choose the most recent version at next reboot
- Set realtime clock, using the client's time (your phone/tablet/computer used for connecting to inki)
- inki reboots and starts displaying live information from the configured source (e.g., seatsurfing server).
No cables, programmer or flashing required — just insert batteries and use your browser.
For more options and logo uploads, see See “Configuration via Web Interface”
Left: browser-based configuration interface at http://192.168.4.1. Right: inki Wi-Fi setup mode.
-
Battery powered No cables needed, runtime up to years
-
Web Interface For setup, configuration and updates via WIFI, bootloader (https://github.com/c0de111/pico_bootloader) automatically chooses most recent firmware version
-
ePaper Display Support Compatible with Waveshare 7.5" V2 and 4.2" V2 displays, retains its content even when powered off.
-
Automatically synchronizes with: seats booked via seatsurfing, data from ccu-historian Shows current booking state and name, layouts, refresh time and display content can be adjusted for room types (office, conference, seminar), or data from ccu-historian
-
Wi-Fi Connectivity Periodically fetches content via HTTP, refresh time freely programmable.
-
Multi-Page Display Up to 8 user-selectable display pages via pushbuttons. See „User-selectable pages“
-
Battery Voltage Monitoring Monitoring of AA / AAA batteries via adc and logged via Wi-Fi, hardware-controlled voltage divider activated only when needed for RTC supply.
-
Energy Efficiency Hardware-controlled shutdown and wake-up via RTC and MOSFET switching — no software sleep required, operated by standard AA or AAA batteries. About 10.000 iteration for large version (7.5", 3 x AA batteries) and about 5.000 iteration for small version (4.2", 3 X AAA batteries). Runtime (depending on wake-up frequency and thus iterations) up to years. For estimation use the script power_consumption_estimate.py
Left: Log of the AA battery voltage of a 7.5" prototype, running for 198 days with 1800-second refresh intervals.
Right: The 4.2" version of the eSign device with its backside visible (including batteries and RTC).
Click any image to view the full-resolution version.
This repository provides all design files, documentation, and code to build your own inki:
-
3D-Printed Enclosure Files and documentation for the modular enclosure with a dovetail mount - (STLs and FreeCAD files).
This animation shows the step-by-step assembly of the 4.2" enclosure.
-
Electronics Custom PCB design with RTC, Pico W, and power management for ultra-low energy consumption (schematics, pcbs, docs).
-
Firmware C-based firmware for RTC wakeup, Wi-Fi sync, Web interface, ePaper display handling, and modular room configuration (C code, build instructions, docs).
Click to watch the 3D enclosure demo video on MakerTube
Eight user-definable pages can be selected during startup by holding combinations of buttons 1–3 and pressing Start.
Page selection logic:
The active page number is determined by summing the values of the pressed buttons:
Button 1 = 1, Button 2 = 2, Button 3 = 4
This allows selecting pages 1–7. Page 0 is the default.
For details, see the “How to Show Pages” screen (Page 4 below).
Displays current room occupancy fetched from the seatsurfing server. The room name, occupant, and space number are shown. This page is shown automatically triggered by the Real Time Clock.
Indicates that the room should not be entered. No network connection required.
A playful feature for indecisive moments. Randomly displays either “Yes!” or “No!” without requiring a network connection.
Shows technical details such as Wi-Fi settings, update intervals, battery voltage (Vcc and Vbat), raw and DST-corrected RTC time, MAC address, and ADC scaling constant.
Explains the startup page selection mechanism using button combinations.
Useful as an on-device quick reference.
Reserved for future features.
Reserved for future features.
Should be self-explanatory.
esign/
├── LICENSE # Top-level: explains dual-licensing
├── hardware/ # Schematics, pcb, 3D printable case
│ ├── LICENSE # CERN-OHL-S v2.0
│ ├── enclosure/ # 3D printable STL files and documentation
│ ├── circuit/ # KiCAD files and documentation
│ └── ...
├── firmware/ # C firmware source, headers, build system
│ ├── LICENSE # Apache 2.0
│ └── ...
├── docs/ # Markdown docs, tips, and background
├── images/ # Photos, renderings, examples
└── README.md # This file
This project contains both hardware and software components, which are licensed under separate terms:
- All content in the /hardware directory is licensed under the CERN Open Hardware License v2 - Strongly Reciprocal (CERN-OHL-S-2.0).
- All content in the /firmware directory is licensed under the Apache License, Version 2.0.
See the LICENSE files in the respective directories for full license texts and terms.
Active development — repository being built step-by-step.
Want to follow or contribute? Star the repo, and stay tuned for updates!
For questions, feedback, or contributions, feel free to reach out via email: