====== CCS811 - CO2 ======
CCS811 air quality monitoring Digital Internal gas sensor
 
the CJMCU-811 is an ultra-low-power digital gas sensor that integrates a sensor and a CCS801-bit MCU with an analog-digital converter (ADC) for detecting indoor air quality, including carbon monoxide (CO) and a wide range of Volatile Organic compounds (VOCs).

{{:components:ccs811.png?nolink&200|}}

====== Code ======
===== Library =====
<code python CCS811.py>
"""
ams CCS811 Indoor Air Quality Sensor
Date:  April 2018
License: This code is public domain
Based on CCS811 datasheet. Inspired by Adafruit and Sparkfun libraries
Tested with Adafruit CCS811 Air quality breakout. Product ID: 3566
Tested on NodeMCU and Wemos D1 Mini (ESP8266) MicroPython v1.8.7-7-gb5a1a20a3
and MicroPython v1.9.3-8-g63826ac5c on 2017-11-01; ESP module with ESP8266
"""

from machine import I2C

class CCS811(object):
    """CCS811 gas sensor. Measures eCO2 in ppm and TVOC in ppb"""

    def __init__(self, i2c=None, addr=90):
        self.i2c = i2c
        self.addr = addr      # 0x5A = 90, 0x5B = 91
        self.tVOC = 0
        self.eCO2 = 0
        self.mode = 1       # Constant power mode; measurement every second
        self.error = False

        # Check if sensor is vailable at i2c bus address
        devices = i2c.scan()
        if self.addr not in devices:
            raise ValueError('CCS811 not found. Please check wiring. Pull nWake to ground.')
        # See figure 22 in datasheet: Bootloader Register Map
        # Check HW_ID register (0x20) - correct value 0x81
        hardware_id = self.i2c.readfrom_mem(self.addr, 0x20, 1)
        if (hardware_id[0] != 0x81):
            raise ValueError('Wrong Hardware ID.')
        # Check Status Register (0x00) to see if valid application present-
        status = self.i2c.readfrom_mem(self.addr, 0x00, 1)
        # See figure 12 in datasheet: Status register: Bit 4: App valid
        if not (status[0] >> 4) & 0x01:
            raise ValueError('Application not valid.')
        # Application start. Write with no data to App_Start (0xF4)
        self.i2c.writeto(self.addr, bytearray([0xF4]))
        # Set drive mode 1 - see Figure 13 in datasheet: Measure Mode Register (0x01)
        self.i2c.writeto_mem(self.addr, 0x01, bytearray([0b00011000]))

    def __string__(self):
        return 'eCO2: %d ppm, TVOC: %d ppb' % (s.eCO2, s.tVOC)
        # doesn't seem to work

    def data_ready(self):
        """returns true if new data was downloaded. Values in .eCO2 and .tVOV"""
        status = self.i2c.readfrom_mem(self.addr, 0x00, 1)
        # bit 3 in the status register: data_ready
        if (status[0] >> 3) & 0x01:
            # datasheet Figure 14: Algorithm Register Byte Order (0x02)
            register = self.i2c.readfrom_mem(self.addr, 0x02, 4)
            co2HB = register[0]
            co2LB = register[1]
            tVOCHB = register[2]
            tVOCLB = register[3]
            self.eCO2 = ((co2HB << 8) | co2LB)
            self.tVOC = ((tVOCHB << 8) | tVOCLB)
            return True
        else:
            return False

    def get_baseline(self):
        register = self.i2c.readfrom_mem(self.addr,0x11,2)
        HB = register[0]
        LB = register[1]
        #baseline = (HB << 8) | LB
        return HB, LB

    def put_baseline(self,HB,LB):
        register = bytearray([0x00,0x00])
        register[0] = HB
        register[1] = LB
        self.i2c.writeto_mem(self.addr,0x11,register)
    
    def put_envdata(self,humidity,temp):
        envregister = bytearray([0x00,0x00,0x00,0x00])
        envregister[0] = int(humidity) << 1
        t = int(temp // 1)
        tf = temp % 1
        t_H = (t + 25) << 9
        t_L = int(tf * 512)
        t_comb = t_H | t_L
        envregister[2] = t_comb >> 8
        envregister[3] = t_comb & 0xFF
        self.i2c.writeto_mem(self.addr,0x05,envregister)
        #return envregister
</code>

===== Usage sample =====

<code python>
from machine import Pin, I2C
import time
import CCS811

i2c = I2C(scl=Pin(5), sda=Pin(4))
s = CCS811(i2c)
time.sleep(1)
while True:
    if s.data_ready():
        print('eCO2: %d ppm, TVOC: %d ppb' % (s.eCO2, s.tVOC))
        time.sleep(1)
        
</code>