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[MISC] How to use a rechargeable battery
Hello,
This is not related to the firmware, but as there are a few experts of the LYWSD03MMC in here, I thought I could try. I've put a rechargeable battery in the sensor, a LIR2032. But this battery has a much higher voltage (3.7V). The sensor is working ok, but the screen is showing some kind of ghost image, so it is difficult to read.
Do you think there's a way to lower the voltage to make this kind of battery usable with a Mijia ?
Can you post a photo? Probably it is a too high contrast of the LCD which is optimized for lower voltages. Maybe you could/must change a SMD resistor to get proper voltage for the LCD again.
That looks exactly as I supposed. Thats a normal behavior of a LCD getting too much voltage. Maybe it is possible to use another resistor for the LCD to get a normal contrast again. Have a look at this video https://www.youtube.com/watch?v=cF49mfYkyw0
That looks exactly as I supposed. Thats a normal behavior of a LCD getting too much voltage. Maybe it is possible to use another resistor for the LCD to get a normal contrast again. Have a look at this video https://www.youtube.com/watch?v=cF49mfYkyw0
Thank you for your answer. Do you know which one should be changed ?
- It is not advisable to exceed the supply voltage more than 3.6V.
- LYWSD03MMC were produced in 6 HW versions. LCD and controllers are different:
For LYWSD03MMC, the HW version is determined by the display and sensor addresses on I2C: README:
| HW | LCD I2C addr | SHTxxx I2C addr | Note |
|---|---|---|---|
| B1.4 | 0x3C | 0x70 (SHTC3) | |
| B1.5 | UART | 0x70 (SHTC3) | |
| B1.6 | UART | 0x44 (SHT4x) | |
| B1.7 | 0x3C | 0x44 (SHT4x) | Test original string HW |
| B1.9 | 0x3E | 0x44 (SHT4x) | |
| B2.0 | 0x3C | 0x44 (SHT4x) | Test original string HW |
Version 1.7 or 2.0 is determined at first run by reading the HW line written in Flash. Display matrices or controllers are different for all versions, except B1.7 = B2.0.
- Connect the diode in series with LIR2032. There will be a voltage drop across it of 0.4..0.6V.
Thank you for your answer. I mostly have 1.5 and 1.6 hardware versions. What kind of diode should I use ? How would you connect it ?
I have HW B1.7 and the display appears to work fine with my LIR2032 batteries at 4.0V. I did run into a different issue of the battery calculation overflowing, which I have submitted a PR ( #524 ) to correct.
Edit: I guess they are a bit overdriven, which makes them difficult to read from an angle, but fine from straight-on. Not really an issue for me, I don't really depend on these visually.
