colindt / wall-display

Raspberry Pi program for air monitoring

Wall Display

A Python program for Raspberry Pi that reads atmospheric data from sensors and displays it on a character LCD. Shows date, time, temperature, humidity, pressure, and CO₂ concentration.

Hardware Diagram

Log Format

All sensor readings are logged to a big-endian binary file called logs/all_data.dat as an array of 22-byte records. Each record's 8 fields are described below:

offset	field name	length (bytes)	type	data source	quantity	units	notes
00	timestamp	4	unsigned int	clock	UTC Unix time	seconds	Python's datetime module automatically handles converting system time to and from UTC unix timestamps. Treat is as unsigned and it lasts until 2106.
04	dps310_pressure_hPa	4	float	DPS310	atmospheric pressure	hPa	single-precision is more than enough to represent the sensor's advertised ±0.002 hPa precision
08	dps310_temp_c	4	float	DPS310	temperature	°C	single-precision is more than enough to represent the sensor's advertised ±0.5°C precision
0C	scd40_co2	2	int	SCD40	CO2 concentration	ppm
0E	scd40_temp_bin	2	unsigned int	SCD40	temperature	(see notes)	To convert to temperature in °C: -45 + 175 * scd40_temp_bin / 2**16 To convert temperature in °C to stored value: int(2**16 * ((scd40_temp_c + 45) / 175)) (This is the same format transmitted by the sensor. See table 11 on page 9 of the datasheet.)
10	scd40_humid_bin	2	unsigned int	SCD40	relative humidity	(see notes)	To convert to relative humidity percentage: 100 * scd40_humid_bin / 2**16 To convert %rH to stored value: int(2**16 * (scd40_humid / 100)) (This is the same format transmitted by the sensor. See table 11 on page 9 of the datasheet.)
12	dht22_temp_c_10	2	int	DHT22	temperature	(see notes)	To convert to temperature in °C: dht22_temp_c_10 / 10 To convert temperature in °C to stored value: int(10 * dht22_temp_c) (The sensor uses a 1 decimal fixed-point representation) If the sensor had an error, the value will be 0x7FFF instead.
14	dht22_humid_10	2	int	DHT22	relative humidity	(see notes)	To convert to relative humidity percentage: dht22_humid_10 / 10 To convert temperature in °C to stored value: int(10 * dht22_humid) (The sensor uses a 1 decimal fixed-point representation) If the sensor had an error, the value will be 0x7FFF instead.

The Python struct format string for this format is ">LffhHHhh".