Arduino library for the ACD10 CO2 sensor (I2C).
Experimental
This library is to use the Aosong ACD10 CO2 sensor. Besides CO2 concentration this sensor also provides a temperature reading.
The CO2 concentration supported by the sensor has a range from 400 ~ 5000 ppm ±(50ppm + 5% reading). This makes the sensor applicable for outdoor and indoor measurements in a normal building setting. The sensor is not suitable for CO2 heavy "industrial" environments.
Warning The temperature range the sensor can measure is UNKNOWN as there is no documentation how to convert the raw data to meaningful one.
The sensor can be read over I2C and over Serial. This library only support the I2C interface (see hardware notes below).
When the sensor starts up it has a pre-heat period of 120 seconds. The library provides functions to check the time since the constructor is called. Note that this not necessarily implies that the sensor is ON. During the preheat period one can make measurements but one should use those carefully as these are less accurate than after the preheat period.
Also important is the calibration of the sensor, although done in the factory, a CO2 sensor needs regular calibration. See datasheet for details.
The sensor must be powered with 5V and uses about 225 mW. This implies the sensor uses 50 mA (@5V) and needs a separate power supply. One must connect GND from the power supply to the GND of the MCU.
Do not apply this product to safety protection devices or emergency stop equipment, and any other applications that may cause personal injury due to the product's failure.
- temperature: 0°C~ +50°C ==> keep away from freezing cold or direct sunlight.
- humidity: 0% ~ 95% RH ==> non-condensing conditions.
- Data refresh frequency: 2 seconds
TOPVIEW ACD10
+--------------------+
pin 6 | o |
pin 5 | o o | pin 1
| o | pin 2
| o | pin 3
| o | pin 4
| |
+--------------------+
| pin | name | description | Notes |
|---|---|---|---|
| 1 | SDA/RX | I2C data | 3-5V |
| 2 | SCL/TX | I2C clock | 3-5V |
| 3 | GND | Ground | |
| 4 | VCC | Power +5V | separate power supply needed. |
| 5 | SET | select com mode | HIGH (or n.c.) => I2C, LOW => Serial |
| 6 | - | not connected |
If pin 5 is not connected or connected to HIGH, I2C is selected (default). If pin 5 is connected to GND (LOW), Serial / UART mode is selected. This latter serial mode is NOT supported by this library.
- https://emariete.com/en/sensor-co2-mh-z19b/
- https://emariete.com/en/sensor-co2-low-consumption-mh-z1311a-winsen/
- https://revspace.nl/MHZ19
- https://www.co2.earth/ - current outdoor CO2 level can be used for calibrating.
- https://keelingcurve.ucsd.edu/ - historical outdoor CO2 level.
- https://github.com/RobTillaart/MTP40C
- https://github.com/RobTillaart/MTP40F
- https://github.com/RobTillaart/Cozir
TODO: Test on Arduino UNO and ESP32
The device has a fixed I2C address of 0x2A (42) so only one sensor per I2C bus can be used. The I2C communication supports 3-5V so any 3.3V MCU should be able to connect. Do not forget appropriate pull up resistors on the I2C SDA and SCL lines.
If one needs more sensors there are some options.
- One could use an I2C multiplexer (see below)
- One could use an MCU with multiple I2C buses.
- One could use a (Two-Wire compatible) SW I2C (outside scope of this library).
Using the VCC as a Chip Select is not advised as the ACD10 has a preheat time of 2 minutes. Every time the power is shut off the pre-heat would run again internally. It is unclear what effect this has on the lifetime and quality of the sensor.
Sometimes you need to control more devices than possible with the default address range the device provides. This is possible with an I2C multiplexer e.g. TCA9548 which creates up to eight channels (think of it as I2C subnets) which can use the complete address range of the device.
Drawback of using a multiplexer is that it takes more administration in your code e.g. which device is on which channel. This will slow down the access, which must be taken into account when deciding which devices are on which channel. Also note that switching between channels will slow down other devices too if they are behind the multiplexer.
See example TCA9548_demo_ACD10.ino
Only test readSensor() as that is the main function.
| Clock | time (us) | Notes |
|---|---|---|
| 100 KHz | default | |
| 200 KHz | ||
| 300 KHz | ||
| 400 KHz | ||
| 500 KHz | ||
| 600 KHz |
TODO: run performance sketch.
#include "ACD10.h"- ACD10(TwoWire *wire = &Wire) optional select I2C bus.
- bool begin() checks if device is visible on the I2C bus.
- bool isConnected() Checks if device address can be found on I2C bus.
- uint8_t getAddress() Returns the fixed address 0x2A (42).
PreHeat functions assume the sensor is (and stays) connected to power.
- bool preHeatDone() returns true 120 seconds after constructor is called.
- uint32_t preHeatMillisLeft() returns the time in milliseconds left before preHeat is complete.
The interface of the sensor is made asynchronous as there is a delay needed of around 80 milliseconds between a request for new data and the availability of that new data.
- int requestSensor() request a new measurement / data.
This must be called before the sensor can be read by readSensor() - bool requestReady() has enough time passed since the call to requestSensor() for the acquisition to happen and to call readSensor()?
- int readSensor() read the values from the sensor. Returns status, 0 == OK, other values are error-codes.
- uint32_t getCO2Concentration() get the last read CO2 measurement in PPM from the device. Multiple calls will give the same value until new measurement is made.
- uint16_t getTemperature() get the last read temperature from the device. Multiple calls will give the same value until new measurement is made.
- uint32_t lastRead() returns the moment of last readSensor() in milliseconds since start. Note the sensor can be read only once every two seconds, less often is better. The library does not guard this two seconds interval (yet).
- void setRequestTime(uint8_t milliseconds = 80) set the time to make a measurement. Default = 80 milliseconds. This can be used to tweak / optimize the performance, so use with care! Use 5~10 milliseconds above the minimal value the sensor still works.
- uint8_t getRequestTime() returns the current request time in milliseconds.
Read the datasheet about calibration process (twice). Incorrect calibration leads to incorrect output.
- bool setCalibrationMode(uint8_t mode) 0 = manual mode, 1 = automatic mode. Returns false if mode out of range ( > 1).
- uint8_t readCallibrationMode() return set mode.
- void setManualCalibration(uint16_t value) as the range of the device is from 400 to 5000, the parameter value should be in this range.
- uint16_t readManualCalibration() read back the set manual calibration value.
Note: One should wait 5 milliseconds between the calibration calls (see datasheet).
- void factoryReset() idem.
- bool readFactorySet() Read back if factory reset was successful.
- uint32_t readFirmwareVersion(char * arr) copies firmware version in array. Minimum length is 11.
- uint32_t readSensorCode(char * arr) copies sensor code in array. Minimum length is 11.
- uint8_t getLastError() returns last error of low level communication.
- improve documentation
- get hardware to test
- investigate the acquisition time of 80 milliseconds
- can it be made shorter by default?
- improve error handling
- rethink function names?
- create unit tests if possible
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