Levoit Classic 300S UART protocol notes

Reverse-engineered notes for the A5 UART protocol used between the main MCU and the WiFi/ESP module in the Levoit Classic 300S humidifier.

This repository is intended to help with replacement WiFi/ESP firmware, local-control experiments, and Home Assistant / MQTT integrations.

Status: working draft, based on UART sniffing and active replacement-controller tests. Most user-facing commands are confirmed. Unknown or not fully proven fields are marked as UNKNOWN, candidate, or observed.

This repository documents the protocol and hardware observations. It does not currently include ready-to-flash ESPHome YAML files or firmware binaries.

What is documented

• UART framing: 9600 8N1, frame header, packet type, payload length, checksum.
• Known frame types:
  • A5-22: WiFi module -> MCU command
  • A5-12: MCU -> WiFi reply / ACK/status reply
  • A5-52: MCU -> WiFi NACK / rejected command
  • A5-02: MCU -> WiFi full status or short event
• Confirmed commands:
  • power on/off
  • display on/off
  • night light raw brightness 0..100
  • timer icon on/off
  • manual mist level
  • auto mode target humidity band
  • sleep mode target humidity band
  • stop-at-target / auto-off behavior command
  • full status request
  • mode-change sync preamble
• 20-byte status payload map.
• Updated p[10] interpretation:
  • p[10] is Target Stop Active / output inhibited by target condition.
  • It is not the stored Stop At Target setting itself.
• Error/fault field candidate:
  • p[19] = 0x00: OK / no error
  • p[19] = 0x01: E1 observed; likely tank Hall sensor / tank-presence fault
  • p[19] = 0x02: E2 candidate / unconfirmed
• Replacement-controller behavior validated on:
  • original ESP32-SOLO-1C / ESP32-S0WD WiFi module
  • newer ESP32-C3-SOLO-1 WiFi module variant
• Hardware component notes:
  • main MCU family candidate: SinOne SC92F84A*
  • display/key controller: AiP650E

Files

• docs/A5_UART_protocol.md — full protocol description.
• docs/ESPHome_replacement_notes.md — practical notes from ESPHome replacement-controller tests.
• docs/hardware_components.md — known/candidate ICs and hardware notes.
• examples/a5_frame_builder.cpp — minimal checksum and command frame builder.

Basic frame format

offset  size  description
0x00    1     0xA5 magic/header
0x01    1     frame type
0x02    1     packet id
0x03    1     payload length low byte
0x04    1     payload length high byte
0x05    1     checksum
0x06    N     payload

Checksum rule:

sum(all frame bytes including checksum) & 0xFF == 0xFF

When building a frame:

checksum = 0xFF - (sum(all bytes except checksum) & 0xFF)

Current replacement-module pin summary

Original ESP32-SOLO-1C / ESP32-S0WD module:

A5 UART RX from MCU TX: GPIO16
A5 UART TX to MCU RX:  GPIO17

Newer ESP32-C3-SOLO-1 module variant:

A5 UART RX from MCU TX: GPIO18
A5 UART TX to MCU RX:  GPIO19

External diagnostic controllers must use level shifting/protection when connected to the MCU-board header. See docs/ESPHome_replacement_notes.md.

Important notes

This is not official Levoit or VeSync documentation. It is a working map recovered from captured UART logs and replacement-module tests.

Physical front-panel button changes may be generated internally by the MCU and reported as A5-02 packets. Replacement firmware must keep listening for MCU-generated packets even when it did not send a command.

The display controller appears to support hardware brightness levels, but the stock MCU UART protocol currently exposes only binary display ON/OFF. Intermediate display brightness values sent through the A5 protocol were rejected in testing.

The original contents of this repository are licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. See LICENSE.