Ink screen temperature and humidity meter

Project Introduction:
While browsing on Xianyu (a Chinese online marketplace), I found a segmented e-ink screen and bought it because it was cheap. I discovered it was the screen for a Miaomiao thermometer and hygrometer, so I intercepted its communication protocol and got it working. After that, I wanted to make something with it, and that's how this e-ink thermometer and hygrometer came about. E-
ink screens far surpass LCD screens in terms of visibility, maintaining good readability even at wide viewing angles and in low-light environments. This project uses a domestically produced CH571+GXHT30 e-ink Bluetooth thermometer and hygrometer (to cut costs, haha).
Project Functions
: 1. Implemented a temperature and humidity meter function with minimal power consumption, aiming for one year of use in 2032.
2. Temperature and humidity data are broadcast via beacon, allowing integration with smart platforms
. 3. Bluetooth parameters can be modified, including full refresh interval, temperature and humidity change interval, and sampling interval.
4. Utilizes Qinheng's official OTA function, eliminating the need for computer connection for firmware updates.
Power Consumption Analysis
Conditions: Temperature and humidity data are collected every 10 seconds, with a change interval of 0.1℃ and 1%, and data is transmitted every 1 second.
Average Beacon power consumption: 20uA. See the attached power consumption analysis report for details.
Segment E-ink Screen:
This screen displays temperature and humidity, emojis, and a Bluetooth icon. The position of each segment is marked on the diagram.
Full-screen refresh time is approximately 2 seconds, with an average current of only about 500uA. The screen requires periodic full-screen refreshes to remove residual artifacts from partial refreshes.
The partial refresh time is approximately 700ms, with an average current of only about 180uA.
The external circuitry of the e-ink screen is simple, requiring only two energy storage capacitors and no external boost circuit for the dot matrix ink bottles. The
software code
references the Bluetooth project provided by Qinheng, and a custom e-ink profile was written to write configuration parameters. Because the CH571 only has 192K of FLASH, OTA updates only update the user app; the Bluetooth library remains unchanged.
Important Note:
Ensure the 10-pin connector for the e-ink screen is correctly soldered and free of cold solder joints. Otherwise, prolonged incorrect commands can burn the screen, resulting in a disastrous situation like this.
Assembly Process:
The outer shell is 3D printed, and a suspended design is used to accommodate the screen in the front panel. Different materials are recommended for the support during printing to ensure a flat screen recess. I used a PLA body with a PETG support surface.
The middle PCB clamp uses an interference fit to hold the main body in place, and the back cover uses four-sided clips. However, because it's 3D printed, the lifespan of these clips might be short.
The front panel is covered with a transparent acrylic protective e-ink screen. The acrylic dimensions are 59.8mm*55.8mm, with a 7mm rounded corner diameter and a 2mm thickness, and it can be attached with UV glue. Anyway, the 3D shell isn't expensive and can be easily disassembled. Compared to Xiaomi's LCD screen, the actual product is a complete knockout.
Screen purchase: [Xianyu] https://m.tb.cn/h.gshtxZ0?tk=1dVY38oOH05 CZ3452 "A Xianyu account from 2016, come and follow them!" You can directly ask this person about 2.5-inch screens, but small batches might be more expensive. If anyone's interested in getting their car reinstalled, I'll get the screen wrapped, haha. You can buy the finished product directly from me on Xianyu (a second-hand marketplace app): [Xianyu link: https://m.tb.cn/h.gs3bTGM?tk=sgJ838LNsITCZ0001] "This is my Xianyu account, come check it out!" QQ group: 703920636. Information is being uploaded slowly.