First read gets a 0 PPM?

[rpavlik]

While I was working on a PR for this repo, I noticed that the first read after each save (and thus reload) was giving good temperature and humidity, but 0 as the CO2 reading. (CLUE running 6.1.0) Not sure if this is expected or not, and whether it's best to deal with just by intentionally dropping the first data_available on the floor, or if there's something else going on.

For reference, a stripped-down copy of my code is here:

# Copyright 2021, Ryan Pavlik <ryan.pavlik@gmail.com>
# SPDX-License-Identifier: Unlicense

from adafruit_clue import clue
from adafruit_scd30 import SCD30
import board
import time

i2c = board.I2C()
try:
    scd = SCD30(i2c)
    have_scd = True
    scd.measurement_interval = 5
except ValueError:
    have_scd = False

def c_to_f(temp):
    return temp * 1.8 + 32

clue_data = clue.simple_text_display(text_scale=2)

last_co2 = "No CO2 meas"
while True:
    clue_data[0].text = "Pressure: {:.3f}hPa".format(clue.pressure)

    # PM25 sensor reads removed here

    clue_data.show()
    if have_scd and scd.data_available:
        clue_data[1].text = "{:.1f}F, {:.1f}%RH".format(c_to_f(scd.temperature), scd.relative_humidity)
        last_co2 = "CO2: {} PPM".format(scd.co2)

    clue_data[2].text = last_co2
    time.sleep(5)

[ladyada]

it does in arduino too, not sure why :/

[caternuson]

FWIW - seems related to the soft reset. Noticed when removing reset() from __init__() that this behavior went away.