CO2 + climate monitor for Flipper Zero. Reads CO2 (MH-Z19B/C) and temperature/humidity/pressure (BME280, DHT22, etc.) through GPIO. Two sensors at once.

PWM + BME280 (good air)	PWM + BME280 (bad air)	UART

Main screen	Menu	Menu

Sensors

Tested

Sensor	Interface	Measures
MH-Z19B	PWM / UART	CO2
MH-Z19C	PWM / UART	CO2
BME280	I2C	Temperature, humidity, pressure

Supported (not tested)

Inherited from unitemp. Should work — report issues if not.

Sensor	Interface	Measures
BMP280	I2C	Temperature, pressure
BME680	I2C	Temperature, humidity, pressure
BMP180	I2C	Temperature, pressure
DHT11	Single wire	Temperature, humidity
DHT12	Single wire	Temperature, humidity
DHT20 / AM2108 / AHT10	I2C	Temperature, humidity
DHT21 / AM2301	Single wire	Temperature, humidity
DHT22 / AM2302	Single wire	Temperature, humidity
AM2320	I2C / Single wire	Temperature, humidity
HTU21x / SI70xx / SHT2x	I2C	Temperature, humidity
SHT30 / SHT31 / SHT35	I2C	Temperature, humidity
GXHT30 / GXHT31 / GXHT35	I2C	Temperature, humidity
HDC1080	I2C	Temperature, humidity
LM75	I2C	Temperature
MAX31725	I2C	Temperature
MAX6675	SPI	Temperature (thermocouple)
MAX31855	SPI	Temperature (thermocouple)
Dallas DS18x2x	1-Wire	Temperature
SCD30	I2C	CO2, temperature, humidity
SCD40	I2C	CO2, temperature, humidity

Based on

• flipper-zero-mh-z19 — PWM CO2 algorithm
• flipperzero_mhz19_uart — UART CO2 protocol
• unitemp-flipperzero — climate sensor drivers

Wiring

MH-Z19 — PWM mode (3 wires)

Flipper PA6 (pin 3)  → sensor PWM (pin 1)
Flipper 5V  (pin 1)  → sensor Vin (pin 4)
Flipper GND (pin 8)  → sensor GND (pin 5)

MH-Z19 — UART mode (4 wires)

Flipper C1  (pin 15) → sensor RXD (pin 3)
Flipper C0  (pin 16) → sensor TXD (pin 2)
Flipper 5V  (pin 1)  → sensor Vin (pin 4)
Flipper GND (pin 8)  → sensor GND (pin 5)

BME280 (I2C, addr 0x76)

Flipper C1  (pin 15) → sensor SCL
Flipper C0  (pin 16) → sensor SDA
Flipper 3.3V (pin 9) → sensor VCC
Flipper GND (pin 8)  → sensor GND

PWM CO2 + I2C climate work together. UART CO2 and I2C share pins 15/16, so can't run at the same time — UART mode disables I2C automatically.

Settings

CO2 sensor (Edit menu)

• CO2 Type — PWM or UART
• CO2 offset — manual correction ±1000 ppm, step 50
• CO2 Alert — sound alert threshold, 800–5000 ppm
• Avg points (PWM) — averaging window 1–30 readings (1 = raw, no smoothing)
• CO2 Range (PWM) — sensor's measurement scale, 2000–10000. See PWM Range below
• Eject (PWM) — clears current reading and resets the buffer. Sensor picks up fresh data if still connected. Use when the reading is frozen or after unplugging

Climate sensor (Edit menu)

• Sensor type (BME280, BME680, DHT22, etc.)
• Temp offset ±10 °C, step 0.1
• Units: temperature, pressure, humidity
• Heat index on/off

General (Settings menu)

• Backlight — 5s, Auto, 1m, 5m, 10m, 20m, 60m, Inf. The app takes direct control of the display backlight, bypassing the system backlight service. 5s keeps the screen dark — the system may briefly flash it on button press, but the app turns it back off within 5 seconds. Auto hands control to the system (default ~30s timeout). 1m–60m keep the screen on, then turn it off after the set period of inactivity on the main screen; any button press resets the timer. Inf keeps the screen always on
• LED Notify — on/off
• Sound Alert — on/off
• Sound Volume — 1–10
• Debug Mode — shows raw PWM data on screen

LED colors

CO2	Color
< 800 ppm	Green
800–999	Yellow
1000–1399	Orange
1400+	Red

Sound alerts

• CO2 crosses threshold up → two rising notes
• CO2 drops back (with 50 ppm hysteresis) → two falling notes
• Cooldown: max once per minute
• LED and sound can be turned off separately

PWM Range

The sensor has a built-in scale — the maximum CO2 it can report. MH-Z19B and MH-Z19C usually ship set to 5000 ppm.

The CO2 Range setting must match the sensor's actual scale. If it doesn't, readings will be proportionally wrong. For example: if the sensor is set to 5000 internally but you pick 2000 in the app, all values will show 2.5x lower.

With PWM wiring you can't read the sensor's range — pick the value that gives correct readings. The actual range can only be checked or changed via UART.

Tradeoff — wider range covers more but reads rougher:

Range	Precision	Max CO2
2000	~40 ppm	2000
5000	~100 ppm	5000
10000	~200 ppm	10000

Freeze indicator

If the PWM sensor stops sending fresh data for 5+ seconds, a freeze label appears next to the CO2 number. The last value stays on screen but marked as stale.

This happens when:

• CO2 hits the sensor's range limit (signal maxes out, nothing to measure)
• Sensor is physically disconnected

To clear a frozen reading — use Eject in sensor settings. If the sensor is still connected, it picks up new data automatically.

Signal processing

PWM: rolling buffer of N readings (1–30, default 5). Sorted, min and max dropped, middle values averaged (trimmed mean). Below 3 readings — median instead. Poll interval: 20 ms.

UART: raw reading from sensor, no averaging. Poll interval: 5 s.

CO2 offset is applied after averaging.

Tested on

• Official firmware 1.4.2
• Unleashed unlshd-086
• Momentum mntm-012

Battery drain

Screen off, 24h: ~ -40% battery

Known issues

• Unleashed + RGB backlight mod: timed backlight modes (5s, 1m–60m) may not turn off the screen. The RGB rainbow timer in Unleashed notification service overrides backlight off commands. This is a firmware-level limitation, not an app bug
• One-time backlight flicker (~30s after launch): the system backlight timer may briefly turn off the screen about 30 seconds after app start or after a button press. The app re-enables it within a few seconds. This is a one-time event per input — not a recurring bug