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209 lines
6.7 KiB
Markdown
209 lines
6.7 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/ML8511/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/ML8511/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/ML8511/blob/master/LICENSE)
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[](https://github.com/RobTillaart/ML8511/releases)
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# ML8511
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Arduino library for the ML8511 UV sensor.
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## Warning
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**Always take precautions as UV radiation can cause sunburn, eye damage and other problems**.
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Do not expose yourself to the sun as UV source too long.
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When using artificial UV light (TL LED laser a.o.) use appropriate shielding.
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## Description
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ML8511 - UV sensor - library for Arduino UNO.
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- 3V3 Sensor so do **NOT** connect to 5V directly.
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- do not forget to connect the EN to either an enablePIN or to 3V3 (constantly enabled).
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#### Breakout
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```
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// +-------+--+
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// VIN |o +-+| mounting hole
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// 3V3 |o +-+|
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// GND |o |
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// OUT |o |
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// EN |o S | Sensor
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// +----------+
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```
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## Operational
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As the sensor / breakout is 3V3 one need to connect to Arduino 3V3.
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The library converts the **analogRead()** to voltages, and it uses a
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reference of 5.0 Volt == 1023 steps as default.
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If one wants to use other ratio e.g. 3.3 volts == 4095 steps, one
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can set those with **setVoltagePerStep()**.
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```cpp
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ML8511 light(A0, 7);
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light.setVoltagePerStep(3.3, 4095);
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```
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It is possible to always enable the sensor by connecting the EN pin to 3V3.
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The value of the enablePin in the constructor should then be omitted
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or set to a negative value.
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When connecting to an Arduino UNO one can use the 3V3 of the Arduino to power the sensor.
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However it is not possible to connect the enable pin directly to the sensor.
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Use a voltage divider (10K + 20K) to convert the 5 Volts to ~3.3 Volts.
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## Interface
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- **ML8511(uint8_t analogPin, uint8_t enablePin = 0xFF)** Constructor,
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if enable is connected to 3V3 constantly one does not need to set the enablePin parameter.
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- **float getUV(uint8_t energyMode = HIGH)** returns mW per cm2, energyMode = HIGH or LOW.
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LOW will disable the sensor after reading.
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- **float voltage2mW(float voltage)** returns mW per cm2 from voltage. To be used when one uses an external ADC e.g. ADS1115
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- **void setVoltsPerStep(float voltage, uint32_t steps)** to calibrate the **internal** ADC used.
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Voltage must be > 0 otherwise it is not set and the default of 5 volts 1023 steps is used.
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This function has no meaning for an external ADC.
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- **float getVoltsPerStep()** idem.
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- **void enable()** manually enable.
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- **void disable()** manually disable.
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- **bool isEnabled()** get enabled status.
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#### Experimental
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WARNING: USE WITH CARE
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- **float estimateDUVindex(float mWcm2)** input in mW per cm2, returns a value between 0 and ~15(?)
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- **void setDUVfactor(float factor)** set the conversion factor
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- **float getDUVfactor()** returns the set conversion factor (default 1.61)
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See below (Experimental DUVindex) how to determine the DUV factor for your sensor.
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_Note:
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The UV index can be very high, in La Paz, Bolivia, one of the highest cities in the world
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the DUV index can go above 20. See link below.
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This is really extreme and it is unknown how the ML8511 sensor (and this library) behaves under such conditions, and how long the sensor would survive.
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Datasheet goes up to 15 mW per cm2, with a default DUVfactor of ~1.61 the measurements could handle DUV of ~24 in theory._
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https://edition.cnn.com/2021/11/03/americas/bolivia-heatwave-highlands-intl/index.html
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## Sensor sensitivity
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Indoors there is very little or no UV light so use a known UV source like
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a black-light or go outside in the sun.
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The formula to convert the ADC reading to mW cm^2 is based upon the graph
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shown in the datasheet. As I have no reference source to calibrate the library
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the accuracy is limited at best. If you know of a calibrated source please let me know.
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The sensor has its peak sensitivity ( >80% ) from λ = 300-380 nm
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with an absolute peak at λ = 365 nm.
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## Experimental DUVindex
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Note: this library is **NOT** calibrated so **USE AT OWN RISK**
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The DUV index can be used for warning for sunburn etc.
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#### DUV index table
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Based upon https://en.wikipedia.org/wiki/Ultraviolet_index,
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| DUV INDEX | Description |
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|:---------:|:------------|
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| 0 - 2 | LOW |
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| 3 - 5 | MODERATE |
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| 6 - 7 | HIGH |
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| 8 - 10 | VERY HIGH |
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| 11+ | EXTREME |
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| | |
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#### Calibrate estimateDUVindex()
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To calibrate the **estimateDUVindex()** function one needs to determine the DUVfactor.
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To do this you need an external reference e.g. a local or nearby weather station.
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You need to make multiple measurements during the (preferably unclouded) day and
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calculate the factor.
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```
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DUV from weather station
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factor = --------------------------
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getUV();
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```
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you do this e.g. once per hour, so you get multiple values.
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You can then average them to have a single factor.
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Hardcode this found value in the library (in the constructor) or better
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use the **setDUVfactor(factor)** call in **setup()** to calibrate your sensor.
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## Version info
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#### 0.1.5 and before
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The formula for the experimental **estimateDUVindex(mWcm2)** is based on
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the following facts / assumptions:
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- (fact) The sensor cannot differentiate between wavelengths,
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so integration with different weights is not possible.
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- (assumption) All the UV is radiated at λ = 300 nm.
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This is the most lethal the sensor can sense > 80%.
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- (choice) All the UV is accounted for 100% for the whole value.
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(Erythemal action spectrum)
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As we cannot differentiate wavelengths, this is the safest choice.
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#### 0.1.6
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The formula is simplified to a single factor that the user needs to determine.
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Below is described how to do the calibration.
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## External ADC
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**float voltage2mW(float voltage)** can be used for an external ADC e.g ADS1015,
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ADS1115 or one of the (fast) MCP_ADC's.
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- https://github.com/RobTillaart/ADS1X15
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- https://github.com/RobTillaart/MCP_ADC
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## More about UV
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https://en.wikipedia.org/wiki/Ultraviolet_index
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## Future
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#### must
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- improve documentation
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- refactor / reorganize readme.md
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#### should
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- test more
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- get unit tests up and running
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- investigate in calibration
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- check performance
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#### could
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- investigate serial UV communication with UV led
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- voltage2mW -> handle negative voltages by taking abs value?
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