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148 lines
6.3 KiB
Markdown
148 lines
6.3 KiB
Markdown
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[](https://github.com/RobTillaart/AnalogUVSensor/actions/workflows/arduino_test_runner.yml)
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[](https://github.com/RobTillaart/AnalogUVSensor/actions/workflows/arduino-lint.yml)
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[](https://github.com/RobTillaart/AnalogUVSensor/actions/workflows/jsoncheck.yml)
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[](https://github.com/RobTillaart/AnalogUVSensor/blob/master/LICENSE)
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[](https://github.com/RobTillaart/AnalogUVSensor/releases)
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# AnalogUVSensor
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Arduino library for an analogue UV sensor.
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## Description
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Image courtesy Tinytronics
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This small (type-less) UV-sensor is powered by 3.3 .. 5 V so it can be used by almost any microprocessor.
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The sensor has an analogue output that is roughly linear with the UV-index (sunlight assumed, see notes).
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| Voltage | UV index | risk of harm | Colour |
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|:---------:|:----------:|:---------------|:---------:|
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| <0.050 | 0 | low | Green |
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| 0.227 | 1 | low | Green |
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| 0.318 | 2 | low | Green |
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| 0.408 | 3 | moderate | Yellow |
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| 0.503 | 4 | moderate | Yellow |
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| 0.606 | 5 | moderate | Yellow |
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| 0.696 | 6 | high | Orange |
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| 0.795 | 7 | high | Orange |
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| 0.881 | 8 | very high | Red |
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| 0.976 | 9 | very high | Red |
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| 1.079 | 10 | very high | Red |
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| 1.170> | 11 | extreme | Purple |
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From this table the formula is derived (spreadsheet) which is pretty linear between UV 1 and 11.
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Between 0 and 1 there seems to be a curve / other linear relation.
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#### Notes
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Note: risk of harm based upon Wikipedia.
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Note: The sensor is not calibrated and the table is indicative for sunlight (warning, assumption!)
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and therefore not suitable for e.g. medical or industrial usage.
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Note: UV radiation will not go through normal glass, so inside (a house) you will most likely always read zero.
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This may of course help to calibrate the zero level of the sensor.
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Note: depending on the light source used, the table above is not correct.
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If one wants to use other values one need to fix the formula in the **mv2index()** function.
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(mv stands for millivolt)
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Note: the output of the sensor is typically 0 .. 1.1 volt. To increase precision one might configure
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the ADC used to match this voltage range. E.g. Arduino UNO can be set to use an internal 1.1 volt reference.
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See Arduino manual **setAnalogReference()**
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Note: for a continuous colour scale check
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- https://github.com/RobTillaart/map2colour
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#### Wavelength sensitivity
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The sensor is sensitive for wavelengths from 200 - 370 nm, so mostly in UVB and UVA region and less in the UVC.
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There is no information about the detailed wavelength sensitivity, so it is not possible to compensate.
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However one could assume that there is a normal (or other) distribution over the 200 - 370 nm range and create
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a compensation table based upon the assumed distribution.
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More about UV see - https://en.wikipedia.org/wiki/Ultraviolet
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#### Related
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- https://github.com/RobTillaart/ML8511
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## Interface
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- **AnalogUVSensor()** Constructor.
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- **void begin(uint8_t analogPin, float volts = 5.0, uint16_t maxADC = 1023)**
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set the parameters of the sensor, analogPin, volts and maxADC to specify the internal ADC.
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Volts and maxADC have a default so these can be omitted if these match.
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- Note: one needs to reset these parameters if the settings of the internal ADC are
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changed e.g. to INTERNAL_1V1 to change the accuracy.
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- **float read(uint8_t times = 1)** Returns the UV index.
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Read the analogue sensor one (or more) times to average the reading.
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This can improve the accuracy of the reading.
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If times == 0 it is set to 1.
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- **float mV2index(uint16_t milliVolt)** MilliVolt to index. Returns the UV index.
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The conversion formula from milliVolt to the UV index is used internally by the **read()** function.
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This function can also be called with a voltage measured with an external ADC.
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The function will return a value between 0.0 and 12.0.
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- **char index2color(float index)** Converts an UV index to the first letter of **G**reen,
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**Y**ellow, **O**range, **R**ed or **P**urple.
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Can be used as indication on a user interface.
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This function can also be called with an index from an other UV index sensor.
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#### Power interface
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Works only if setPowerPin is called properly.
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- **void setPowerPin(uint8_t powerPin, bool invert = false)**
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Can be used to control the power of the sensor e.g. for low power mode.
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Optionally one can set the invert flag to **true** to invert the **HIGH LOW** levels
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e.g. when the analogue sensor is switched through a MOSFET.
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- **void switchOff()** switch off the power of the sensor.
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- **void switchOn()** switch on the power of the sensor.
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## Future
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#### Must
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- verify vs calibrated sensor
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#### Should
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- investigate with different light sources (UVled, TL, sunlight).
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- move powerPin setting to constructor (breaking 0.2.0 ?)
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#### Could
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- investigate angle sensitivity e.g. if the UV light comes from an angle - cosine law.
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- see https://github.com/RobTillaart/BH1750FVI library
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- investigate response time to stabilize e.g. does it react fast on clouds.
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- investigate time needed to first (stable) measurement.
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- add code for external ADC (see ACS712)
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- add mV to RGB colour?
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#### Wont
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- **index2time()** calculate max exposure time?
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- dangerous advice, so better keep that out of the library ?
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- **uint32_t index2RGB(float index)** full (smooth) colour RGB mapping.
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- created a https://github.com/RobTillaart/map2colour lib for this feature
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to keep footprint in this library small.
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## Sponsor
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The development of this library is sponsored by [TinyTronics, Netherlands](https://www.tinytronics.nl/shop/nl).
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