MHZ19 mhz19 = MHZ19(rx_pin,tx_pin);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
unsigned long time;
MHZ19 mhz19 = MHZ19(rx_pin,tx_pin);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
unsigned long time;
digitalWrite(led_yellow_pin, co2 >= co2_warning_thr && co2 < co2_alarm_thr);
digitalWrite(led_green_pin, co2 < co2_warning_thr);
digitalWrite(led_yellow_pin, co2 >= co2_warning_thr && co2 < co2_alarm_thr);
digitalWrite(led_green_pin, co2 < co2_warning_thr);