Overview

Combining Adafruit’s CCS811 gas sensor with a Circuit Playground Express and two NeoPixel Sticks we can quickly put together a mask that displays our breath attributes. This setup will monitor temperature, carbon dioxide and total volatile organic compounds. The sensor is easy to work with using it’s I2C interface and pre-calibrated ranges. A mask is an ideal wearable as it provides a place to house the electronics as well as an option for continuous monitoring as it is a hands free device that could be adapted for exercise or sleep. The gas sensors TVOC monitoring can be used as an indicator of ketosis as it will detect acetone levels on the breath which is a by-product of producing ketones. CO2 levels can also be a helpful indicator of how much glucose is being burned versus fats.

Materials

We will be soldering the CCS811 gas sensor and NeoPixel RGBW Sticks to a quarter sized perma protoboard and the Circuit Playground Express.

The mask will need to have several small holes cut into it so we can run the wires for the Circuit Playground Express and NeoPixel Sticks. We will use ordinary nylon sewing string to adhere the components to the mask. 

I've placed the Circuit Playground Express on the blank side of the mask. The other side has a small plastic air filter so we will place a single NeoPixel Stick on that side.

Asssembly

This nickel plated nibbling tool has been a staple in my lab for the last fifteen years. It makes easy work of trimming down PCBs and knocking off sharp corners. This quarter sized perma-proto board can fit into the mask as is, but I split it in half to save space.

Nibble, nibble, nibble. 

Solder 2" leads to each of the NeoPixel sticks. We only need to use the DIN, 5V and GND.

Once the electronics are attached to the outside of the mask via sewing through the mount holes and unused pins we can start soldering wires to the perma-proto board. 

This above wiring diagram shows which connections we need to put in place. Try and use 2" leads between components so it is to access the proto-board with a soldering iron. 

Final hookup with all the components connected.

CircuitPython Code

The Circuit Playground Express boards can run CircuitPython — a different approach to programming compared to Arduino sketches. In fact, CircuitPython comes factory pre-loaded on the Circuit Playground Express. If you’ve overwritten it with an Arduino sketch, or just want to learn the basics of setting up and using CircuitPython, this is explained in the Adafruit Circuit Playground Express Guide

To use the code below, plug the Circuit Playground Express into USB…it should show up on your computer as a small flash drive…then edit the file “main.py” with your text editor of choice. Select and copy the code below and paste it into that file, entirely replacing its contents (don’t mix it in with lingering bits of old code). When you save the file, the code should start running almost immediately.

import time

import adafruit_CCS811
import board
import busio
import neopixel

# i2c interface for the gas sensor
i2c_bus = busio.I2C(board.SCL, board.SDA)
ccs = adafruit_CCS811.CCS811(i2c_bus)

# Three Different NeoPixel 8 LED Lengths for Output:
# 1 - Temperature - Circuit Playground Built-In LEDs
# 2 - Total Volatile Organic Compounds [strip]
# 3 - Co2 Output - NeoPixel [strip]
num_leds = 8
temperature_pix = neopixel.NeoPixel(board.NEOPIXEL, num_leds, brightness=.1)
tvoc_pix = neopixel.NeoPixel(board.A1, num_leds, bpp=4, brightness=.1)
co2_pix = neopixel.NeoPixel(board.A2, num_leds, bpp=4, brightness=.1)
led_draw = .05  # delay for LED pixel turn on/off

# wait for the sensor to be ready and calibrate the thermistor
while not ccs.data_ready:
    pass
temp = ccs.temperature
ccs.temp_offset = temp - 25.0


def clear_pix(delay):
    # clear all LEDs for breathing effect
    for i in range(0, num_leds):
        temperature_pix[i] = (0, 0, 0)
        co2_pix[i] = (0, 0, 0, 0)
        tvoc_pix[i] = (0, 0, 0, 0)
        time.sleep(delay)


def co2_led_meter():
    # Show Carbon Dioxide on a NeoPixel Strip
    co2_floor = 400
    co2_ceiling = 8192

    # Map CO2 range to 8 LED NeoPixel Stick
    co2_range = co2_ceiling - co2_floor
    co2_led_steps = co2_range / num_leds
    co2_leds = int((ccs.eCO2 - co2_floor) / co2_led_steps)

    # Insert Colors
    for i in range(0, (co2_leds - 1)):
        co2_pix[i] = (255, 0, 255, 0)
        time.sleep(led_draw)


def tvoc_led_meter():
    # Show Total Volatile Organic Compounds on a NeoPixel Strip
    tvoc_floor = 0
    tvoc_ceiling = 1187

    # Map CO2 range to 8 LED NeoPixel Stick
    tvoc_range = tvoc_ceiling - tvoc_floor
    tvoc_led_steps = tvoc_range / num_leds
    tvoc_leds = int(ccs.TVOC / tvoc_led_steps)

    # Insert Colors
    for i in range(0, (tvoc_leds - 1)):
        tvoc_pix[i] = (0, 0, 255, 0)
        time.sleep(led_draw)


def temp_led_meter():
    # Show Temperature on Circuit Playground built-in NeoPixels
    temp_floor = 23
    temp_ceiling = 36

    # Map temperature range to 8 LEDs on Circuit Playground
    temp_range = temp_ceiling - temp_floor
    temp_led_steps = temp_range / num_leds
    temp_leds = int((ccs.temperature - temp_floor) / temp_led_steps)

    # Insert Colors
    for i in range(0, (temp_leds - 1)):
        temperature_pix[i] = (255, 255, 0)
        time.sleep(led_draw)


while True:
    # print to console
    # - co2
    # - total voltatile organic compounds
    # - temperature in celsius
    print("CO2: ", ccs.eCO2, " TVOC:", ccs.TVOC, " temp:", ccs.temperature)

    co2_led_meter()
    tvoc_led_meter()
    temp_led_meter()

    time.sleep(.5)
    clear_pix(led_draw)

Wear It

The Circuit Playground Express will need to initially plugged in for 48 hours so that the CCS811 sensor can burn in. The spec sheet suggests an additional 20 minute warmup before each use. 

If you wish to see the raw data you can connect to the Circuit Playground Express micro USB connector to a computer and watch the console output.  On Linux or OS/X the screen command the /dev/*modem* device is the easiest way. 

$ ls /dev/tty.usbmodem*
/dev/tty.usbmodem1421
$ screen /dev/tty.usbmodem1421 115200

The above command will show the name of your Circuit Playground Express and connect you to the console on OS/X. You will probably need to adjust the usbmodem#### numbers to match your exist device.