Sensors

This is a list of sensors and their related information.

MH-Z19 CO2 Sensor

These CO2 modules cost about $17 USD. They come in 3 models: 0-2000PPM, 0-5000PPM, and 0-10000PPM.

Interface: PWM or UART

See: MH-Z19 Carbon Dioxide Sensor

CCS811 Air Quality Sensor

The CCS811 air quality sensor can measure Volatile Organic Compounds (VOCs). The internal microprocessor will calculate the equivalent CO2 value from the VOC measurement. These cost about $8 USD. The device or the library driving it is causing issues with the I2C bus which causes the entire bus to freeze. If you want to measure CO2, I would recommend using the MH-Z19 which actually measures CO2 rather than eCO2.

The datasheet can be found at: https://www.sciosense.com/wp-content/uploads/2020/01/CCS811-Datasheet.pdf

Pin Number	Pin Name	Description
1	VCC	Power supply for the module can typically 3.3V is used
2	GND	Ground of the module, connected to ground of the circuit
3	SCL	Serial Clock Line, used to provide clock pulse for I2C communication
4	SDA	Serial Data Address, used to transfer the data through I2C communication
5	WAK	Wake (active low)
6	INT	Interrupt (active low)
7	RST	Reset (active low)
8	ADD	Single address select bit to allow alternate address to be selected

To use the sensor:

1. Connect Vcc and Ground
2. For a ESP8266, connect SCL and SDA (I2C) to D1 and D2 respectively.
3. Connect WAK to ground

Using I2C, the device is on address 0x57.

I2C Freezing Issue

The sensor randomly causes the I2C bus to freeze after an hour or so. This issue is discussed at https://github.com/arendst/Tasmota/issues/3364.

One proposed solution by Frogmore42 is to add a delay in the Adafruit library:

// in Adafruit_CCS811::read
	Wire.endTransmission();
	delay(1);
	Wire.requestFrom((uint8_t)_i2caddr, read_now);

Sensor Broke?

The first sensor I tried to use worked for a bit, but the I2C issue cropped up. I then soldered it to a protoboard thinking the issue may be related to the breadboard, but then it completely stopped working. ReadData returned 24 which suggests an issue with the heater?

MQ135 Air Quality Sensor

This module will return a high signal when the air quality meets a certain criteria.

DHT 11, DHT22

The DHT11 is a digital temperature and humidity sensor. They are notable by their blue perforated plastic package. The DHT11 is created by Aosong Guangzhou Electronics Co. Ltd. Each unit costs around $1.5 USD.

The DHT22, also called AM2302, RHT03, is similar to the DHT11 but offers a slightly wider operating temperature range and higher temperature and humidity resolution. The DHT22 is slightly more expensive at around $3 USD per unit.

The difference between the two modules are outlined in the table below.

	DHT11	DHT22
Relative Humidity Operating Range	20 ~ 90%	0 ~ 100%
Relative Humidity Accuracy	±5%RH	±2%RH (Max ±5%RH)
Humidity Resolution	1%RH	0.1%RH
Humidity Repeatability	±1%RH	±1%RH
Humidity Hysteresis	±1%RH	±0.3%RH
Long-term Stability	±1%RH/year	±0.5%RH/year
Temperature Operating Range	0 ~ 50°C	-40 ~ 80°C
Temperature Accuracy	±2°C	±0.5°C
Temperature Resolution	1°C	0.1°C

BMP085, BMP180, BMP280

These BMPs are atmospheric pressure sensors. They use I2C or SPI. The BMP280 appears to have superseded and are readily available on Ebay for around $0.50 and $1 USD each.

The BMP280 I obtained appear on address 0x76. If you are using the Adafruit library, you need to use the BMP280_ADDRESS_ALT address.

MAX30102

The MAX30102 is a heart rate monitor and pulse oximeter biosensor. These modules cost about $2 USD on AliExpress.

Using I2C, this has address 0x5A.

HC-SR501 Infrared Motion Sensor

The SR501 is an infrared motion sensor. They cost around $1.5 USD each. It has 2 potentiometers that are used to adjust the detection sensitivity and duration of the signal. The middle output pin gives a 3.3V signal when motion is detected and resets back to ground after a period of time.