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Датчик температуры и влажности DHT22/AM2302

Датчик температуры и влажности DHT22/AM2302

Датчик температуры и влажности DHT22/AM2302


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XIAOMI MIAOMIAOCE TEMPERATURE E-INC - ДАТЧИК ТЕМПЕРАТУРЫ И ВЛАЖНОСТИ С ДИСПЛЕЕМ + РАЗБОРКА Датчик температуры и влажности DHT22/AM2302

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Датчик температуры и влажности DHT22/AM2302


Датчики температуры и влажности DHT11 5 DHT22 и Arduino В статье рассмотрены основы работы с недорогими датчиками температуры и влажности серии 5.
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Датчик температуры и влажности DHT22/AM2302

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Датчик температуры и влажности DHT22/AM2302


Продолжаем серию уроков “Arduino для начинающих”. Сегодня мы разберем подключение к Arduino датчиков температуры и влажности DHT11 и DHT22.

Датчик температуры и влажности DHT22/AM2302


Датчик температуры dht-22 5 относительной влажности воздуха. Характеристики.

Датчик температуры и влажности DHT22/AM2302

Влажность от 0 до 100% (+- 5%) Температура от -40 до +80 °С (+- 0.5%) Данные считываются с точностью до десятых. Питание 3-5 В Wide range of Hygrometers: DHT22, AM2302, AM2320, AM2321, SHT71, HTU21D, Si7021, BME280 Introduction Previous experiments looked at and.
Here I have added five new devices meaning this test now covers most commonly available low-cost digital hygrometers.
This page will present only new results.
For details of how the experiment works.
Comparison of the packaging of the various devices.
Clockwise from the top left, the SHT71 and AM2321 both use 1.
The AM2320 is, I think, the same as the AM2321 but in a package that is compatible with the AM2302.
The devices on the lower row are all shown mounted on third party break-out boards that make it easy to interface the surface mount device to 2.
The sensor itself is the small square component in the top right of each board.
Note that the break-out воскресення SC&T HKM01R Дополнительный приёмник HDMI прав at the bottom left are marked to accept Si7021, SHT21 or HTU21.
The right hand device without the white protective cover is an HTU21D.
The membrane obscures the manufacturer's mark on the left hand device, but reading the internal serial number shows it to be an Si7021.
The Devices and Test Apparatus Aosong AM2302 Also commonly known as DHT22.
Device E was selected as the I originally started with.
It is physically a little smaller, but with identical pin-out.
The one-wire serial of the AM2302 is retained making this a simple drop-in replacement.
It might be electrically identical.
There is some suggestion from the manufacturer's web site that this might already be discontinued and replaced by AM2322.
I am not sure.
The internals of these devices are not exactly the same as the DHT22 because they do not exhibit the very distinctive.
Sensirion SHT71 The same device as was.
In normal use they are interchangeable both in terms of specification and communications protocols and even have the same I2C address so are drop-in replacements for each other.
Similarly the Sensirion SHT21 not included here also has a near identical specification and interface.
I have seen the same third party generic break-out boards being sold with any one of these devices attached.
The one difference I have found and possibly the only way to be sure which device you have is in the devices' unique serial numbers for which each manufacturer uses a slightly different format, detailed in their respective datasheets.
So long as you do not attempt to read the device serial number, these three sensors function identically.
That is not to say they will all perform identically.
Though equivalent for most normal use, the precise specification details do differ, most particularly in their.
For this test I am running one device each, with and without.
The intent had been to include an identical pair of sensors with and without the cover, however when my devices arrived I found the retailer had sent me HTU21s without the cover and Si7021s with the cover.
It was only by reading the internal serial numbers I was able to ascertain that.
Though not discussed in detail on this page, the.
My conclusion was that is has virtually no impact at all.
Be careful with variable types in your software.
This is a good thing because it allows some head room for small errors in the calibration.
The 5 version of my code however used unsigned variables which caused numeric underflow and 0% ended up getting read as 3500%.
Bosch BME280 This device is a bit different.
First, unlike all the other devices tested it includes a barometer.
Though an interesting addition and I will write about it elsewhere, for the present report I present only the temperature and humidity data.
Second, it possibly works on an entirely different physical principle from the other sensors here.
As far as I have been able to acertain, all the other devices are polymer capacitance hygrometers.
The Bosch website, datasheet and press releases contain no information that I have been able to find about what is inside the BME280.
Currently I am operating on a belief that it is a resistive sensor, measuring the electrical resistence through a porous film rather than the capacitance across a film like the other devices.
Many thanks to Nava Whiteford who has sent me some.
In those images, the lower die looks like a typical MEMS barometer so the upper die must presumably be the hygrometer and I am guessing that we see a pair of almost square electrodes and the device is measuring the resistence of the cracked film that spans between them.
They seem to under-promise and over-deliver, so a priori I am not expecting problems outside the specified range.
Зарядное устройство Olight Omni-Dok to the other devices though, this can occur straight out of the box, in the factory default configuration.
In its default configuration, rather than taking a reading on demand, the device continuously reads values as fast as it can, returning the latest available value on request.
The sampling rate is controlled by setting the 0xF5 memory register and the various speed options are defined in the datasheet.
When running at the default full speed my device returned temperatures 0.
At one sample per second values agreed with the polled operating mode where the device was put to sleep between readings.
The Aosong data sheets do not specify maximum tolerances for most parameters, just 'typical' values.
It would therefore seem that any particular device is not guaranteed to meet these specifications.
For all the other devices the numbers above are the maximum tolerances and most also offer better 'typical' specifications.
The Test Apparatus Apparatus setup is essentially though a new board had to be built to hold nine devices inside the jars.
The AM2302 and SHT71 devices have proprietary one-wire serial interfaces and were addressed independently, each using a separate GPIO pin as in the previous experiments.
All the other sensors were multiplexed onto the I2C bus.
I2C is able to address multiple devices on a single bus so long as each has a different address, but since I have multiple samples of the same device I am not able to identify each one uniquely.
I therefore use a so that only one of the devices is connected to 5 I2C bus at a time.
The devices are powered continuously, but the I2C IO lines are briefly connected to each device in turn.
This would not have been required if I had only one each of the different device models.
The reference calibration sources are the same as before, and distilled water.
Sensors were allowed to stabilise for a few hours with each solution.
The software automatically steps the temperature over a pre-defined range, allowing the readings to settle at each temperature and logging a reading to a database before stepping to the next temeperature.
Results Throughout the following plots you will notice the data for sensor G are a little more sparse than как сообщается здесь others.
Both my AM2320 devices fail intermittently above 50% RH, just returning bytes of 00 or FF.
They are worst in the range 50-70% where I got almost no readings.
Below that I had not problems and above they were intermittent but fine most of the time.
I never found a cause or have any suggestion for why they should fail to produce output in such a narrow range of humidity.
At least the values are obviously wrong and an extra function was added to the microcontroller code to simply reject the bad data.
The others all continue uneffected but values were only logged from this sensor when they were sensible.
Similarly, the AM2321 device J failed to return values when the humidity was above 90%.
Whenever I used H 2O 100% or K 2NO 3 92% the sensor would work for about 10-15min and then freeze, refusing to even repond to I2C communication requests.
It worked again immediately once the humidity dropped.
Again, I have not found a fix and simply did not log data from this sensor above 90%.
Part 1: As a Function of Humidity First we look at the varying response of the sensors to different reference humidities 0—100%.
Figures 3 and 4 contain the same data plotted with different axes.
Figure 3 shows the actual relative humidity values measured and Figure 4 shows the deviations from a perfect calibration.
The manufacturers' specifications are all defined at 25°C so I highlight those data in red.
Data obtained at other temperatures are shown in blue.
Plots of the humidity values from each sensor plotted against the expected humidity for each reference solution.
The shaded grey region is the specified tolerance from the manufactuers' datasheets.
All data collected, irrespective of temperature, are shown as blue dots.
Red crosses are just those data obtained at 25±1°C, so any that lie outside the shaded region fail to meet the specification.
These same data are presented in more detail in Figure 4.
Plots showing the deviation of humidity values from the known reference value.
These plots show the error of each sensor as a function of humidity.
The shaded grey region is the specified tolerance from the manufacturers' datasheets.
All data collected, irrespective of temperature, are shown as blue dots.
Red crosses are just those obtained at 25±1°C, so any that lie above or below the shaded region fail to meet the advertised specification.
Where blue dots scatter outside the shaded region it indicates a drift in the calibration as a function of temperature.
Red lines are quadratic fits to the 25±1°C data.
Both of the above figures have where you can see earlier results for SHT71 and AM2302 E, F.
The other six are new and this is their first test.
Part 2: As a Function of Temperature In the red data are measured at 25±1°C and the blue data at other temperatures.
The large scatter of the blue points however show that the calibration degrades rapidly with varying temperature.
As previously noted, this is my cherry-picked, best AM2302 from a sample of six.
In 5, device K an HTU21D seems to lie just Ян Маршан Человек-собака outside its specified tolerance at 25°C but has the very substantial advantage of behaving consistently over temperature.
In different applications, absolute accuracy at 25°C or a small temperature dependence might be preferable.
Easily the best performers though are the BME280 which are both accurate and consistent over the range tested.
To show those differences in more detail I present plots for a single chemical as the temperature is systematically varied.
Included are NaCl, NH 4NO 3 and MgCl.
The humidity axis has been set to the same range in all three plots in order to fairly represent the relative gradients of the lines.
Devices E, F and SHT71 are the same units there and here.
They have remained fairly consistent over the six months between the two experiements.
The smaller, round data points are the published reference values.
Shown as red boxes and a linear fit are measurements for all sensors with saturated sodium chloride over the temperature range 5—35°C.
Plotted for comparison are values taken from the published literature.
Blue data are fromcyan data fromgreen from and yellow.
The thin black line is an ensemble fit to them all, weighting all equally.
Shown in red boxes and a linear fit line are measurements for all sensors with saturated ammonium nitrate over the temperature range 5—35°C.
Plotted for comparison are values taken from the published literature.
Cyan data from and yellow from.
The thin black line is an equally weighted fit to both.
Shown as red boxes and a linear fit are measurements for all sensors with saturated magnesium chloride over the temperature range 5—35°C.
Plotted for comparison are values taken from the 5 literature.
Blue data are fromcyan data fromgreen frommagenta are the and yellow.
The thin black line is an ensemble fit to them all, weighting all equally.
The BME280 shows outstanding calibration throughout.
For the other sensors, where the slope of my data matches the slope of the reference data e.
Where the slopes of the measurements and reference data differ e.
Part 3: As a Function Simultaneously of Temperature and Humidity Finally, if a sensor is to be used to measure humidity under a range of varying temperatures a full bivariate calibration is required.
The curves in are effectively cross sections through these surfaces.
It has been moved out into a separate document since rendering nine surfaces simultaneously proved an excessive load for some web browsers.
A 'perfect' sensor would be a featureless green-yellow plane at zero.
Blue shows low readings and red are high.
Surfaces showing deviation of each sensor from the true relative humidity as a function of temperature and humidity.
A 'perfect' sensor would be a featureless green plane at zero.
Blue shows low readings and red are high.
Hysteresis Hysteresis is the tendancy of a physical system's state to depend on its past state.
The word is derived from ancient greek for 'lagging behind'.
A sensor with hysteresis will tend to give low readings if it has recently been exposed to dry air and tend to read high when it has recently been exposed to wet air.
Here I use the term hysteresis only to refer 5 the lagging of the sensor behind the current conditions.
I do not distinguish between the case of the sensor having a very slow response many hours but eventually asymptotically approaching the 'true' value and the case of a sensor that is permanently biased by its history and would never reach the same 'true' value when approaching from above or below.
To test for this I held all sensors at a constant 25°C but exposed them in ordered sequence to K 2NO 3 92%NH 4NO 3 60%MgCl 33%NaOH 7%MgCl 33%NH 4NO 3 60%K 2NO 3 92%.
Each humidity level was held for twelve hours and the measured value logged every half hour.
Two complete cycles of the loop from wet to dry and back to wet were performed.
Deviations from the known reference value as humidity is systematically cycled from high to low and back to high.
Two complete cycles of 92%, 60%, 33%, 7%, 33%, 60%, 92% are shown.
For most sensors the traces followed on rising and falling humidity are reasonably close together, showing little hysteresis нажмите чтобы прочитать больше />A couple of sensors do show a strong effect.
Notes on particular sensors: AM2302 F output saturates at 99.
The AM2321 generally failed to give any output for K 2NO 3.
The AM2320 generally failed to give any output for NH 4NO 3.
It occaisionally provided an intermittent reading, but largely fails for по этому сообщению around 50-70%.
Figure 9 shows the hysteresis results.
The red points are the same 25°C data as in previous plots.
The dark grey lines are the new hystersis test and create envelope inside which all the readings will fall.
As expected, all sensors do show the tendency to read systematically high when the humidity is decreasing and read low when humidity is rising.
However, for all devices except the Si7021 and AM2320 the effect is small and the width of the envelope is not larger than the scatter of data points already observed.
This means that with due regard to the errors already determined, hysteresis is not a signficant extra effect.
It is already included in the errors we have observed.
It is true though that all values will be slightly biases one way or the other as conditions change.
Temperature Accuracy Though primarily interested in humidity, I present a brief comparison of the temperature measurements.
I made no attempt here to establish an absolute temperature calibration and simply compare each sensor to the ensemble average of all nine sensors.
A separate document что Комбинированная плита Ardo KT6C4G00FSIX тут and also demonstrates that though the results here are strictly only relative, within a couple of tenths of a degree they are also good representations of the absolute accuracy.
Plots show temperature returned by each device compared to читать далее average of all nine.
Plots showing deviation of each device's own temperature from the average of all nine, plotted as a function of temperature.
All agree within about 0.
The Bosch sensors consistently gave the highest values and looking at show the largest scatter, suggesting poorer repeatability.
However, investigating in more detail, the Bosch thermometers are very weakly humidity sensitive.
Repeatability at a fixed humidity is very good.
The difference is small 0.
In contrast, the AM2320 device G shows little error as a function of humidity but has the largest error as a function of temperature.
Plots showing deviation of each device's own temperature from the average of all nine, plotted as a function of humidity.
Only for the BME280 is there a convincing detection of the thermometer being slightly humidity sensitive.
Response Speed All respond to changes faster than humidity is likely to change naturally, but speed may occaisionally by an issue of interest, for example when measuring a forced flow of air.
посетить страницу источник were taken once every six seconds.
For this test the BME280's internal smoothing filter was switched off.
For all other data on this page the filter was enabled.
It is a feature of all the AM23xx devices that they return a cached value from memory meaning they will always appear to respond to a change one reading 6 seconds later than the others.
For this reason I plot both the raw data where the AM23xx devices can all be seen to lag by one reading and also a version where that offset has been artifically removed.
The left panel shows the actual results you would get when using the device and the right panel more directly compares the intrinsic physical response of the sensor elements.
Time response of the devices when exposed to a sudden upwards change in humidity.
Left panel shows data directly from the sensors.
Since the AM23xx devices return a previously cached value, they show the step change with a lag of one data point.
In the right hand panel the lag has been arbitrarily removed and the values normalised in order to compare the intrinsic response speed of the sensor elements.
Time response of the devices when exposed to a sudden downwards change in humidity.
Left panel shows data directly from the sensors.
Since the AM23xx devices return 5 previously cached value, they show the step change with a lag of one data point.
In the right hand panel the lag has been arbitrarily removed and the values normalised in order to compare the intrinsic response speed of the sensor elements.
The HTU21D and SHT71 show the fastest response.
Most of the others seem comparable to each other except the Si7021 which is the one major outlier.
This is the device with a protective cover over the sensor and though it may seem reasonable that the membrane would slow the response, showed it has almost no effect, slowing the devices readings by only about 1sec.
The Https://greenl66.ru/100/plitkorez-hilti-dch-300-korobka.html is a lot slow slower than all the others, which I assume to be a deliberate design choice by the manufacturer to make the sensor insensitive to insignificant, rapid fluctuations in humidity and 5 better represent the wider prevailing conditions.
For example, with the highly responsive HTU21D, I often see spikes and wobbles in the readings as I move around the room, stiring the air.
Commentary on Each Sensor Update March 2017 : I have a major revision of these conclusions in preparation.
There is still a long way to go and data collection is ongoing, but I want to be as open as possible.
Newer tests have suggested that in my previous tests I got lucky with an excellent Bosch specimen but possibly had received a damaged Sensirion device.
In the test described here, the BME280 was the clear winner, but I do not want anyone to interpret that as definitive or a general result.
In my ongoing tests, the Bosch and Sensirion devices are indistiguishable at the limit of what I can measure.
Work is still in progress.
Bosch 5 BME280 Within the data obtained here, the BME280 is the undisputed winner.
It is the most accurate at the specified 25°C and it shows the least dependence on temperature.
The hysteresis curve traces a tight envelope and was highly на этой странице on the two cycles performed.
It is also the only model for which every device I own performs within specification.
The difference is so stark that it leads me to believe the sensing element is in some way fundamentally different from the other devices.
My current supposition is that it uses a resistive film rather than a capactive film.
These two particular BME280s consistently read a higher temperature than all the other devices, though others I have tested subsequently in my investigation of have not all followed that pattern.
I am not suggesting all BME280s read hot.
They are the only devices tested to show a measurable humidity dependence in their thermometer.
Again I wonder хотите Светильник Citilux Дрезден CL409111, E27, 100 Вт этого this suggests fundamentally different sensor technology from the other devices.
In any case, they fulfill the manufacturer's specified 1.
AM2302 DHT22 In line with previous tests, I would judge the accuracy of my devices to be around 5%.
Device E, cherry picked as the best from my set of six, has a calibration at 25°C that is almost the equal of any device tested, but it shows a significant temperature dependence when away from these ideal conditions.
Over two years, three of the original six devices have failed.
Both my AM2320s exhibit the same intermittent fault of failing to return any data when humidity is in the range 50-70% RH.
Oddly they appear to work reliably above and below that range.
I never got to the bottom of whether this was something wrong in my set-up or an intrinsic sensor fault.
Currently I am attributing it to bad luck in my getting a couple of faulty devices rather than a systematic fault with this model.
Similarly the AM2321 intermittently fails to return a value above about 90% but works reliably at lower humidities.
The AM2320 tested here shows quite a strong hysteresis though it is difficult to judge because of all the missing data points for NH 4NO 3 60%.
In summary, they appeared similar to the DHT22 most of the time, but I had so many different intermittent problems I do not intend to use these devices in future experiments.
Sensirion SHT71 See 'Update March 2017 ' above.
This run confirms my previous experiments with this device.
Absolute accuracy seems comparable to the other sensors apart from the BME280.
Thermal stability, which I think it often more important than absolute accuracy at 25°C, is better than most.
The data scatter is small and the calibration error is linear in both the humidity and temperature directions.
Looking at that the bivariate temperature:humidity 5, the SHT71 surface is nearly as 'flat' as the BME280s, but it is tilted.
The hysteresis envelope was nice and tight.
It seems well made and has not yet shown any problems in well over two years of continuous operation.
Apart https://greenl66.ru/100/tverdotelniy-nakopitel-pqi-s527-128gb.html that linear tilt in the temperature:humidity surfaces, this device seems to perform very nicely, which makes me wonder if I simply have a poor device.
A small adjustment to the internal calibration parameters could possibly bring this device to very nearly match the BME280.
My current hypothesis is that the sensor element is contaminated and I have some experiments ongoing March 2017 to investigate that.
Measurement Specialties HTU21D I have nothing much specific to say 5 this, but I mean that in a good way.
In my tests it did exactly what it was supposed to.
The absolute errors were a little larger than advertised, but repeatability was good and the thermal dependence not too severe.
Hystersis was almost undetectable.
It is a nice compact and apparently robust unit, especially with the optional cover screen.
It has a very rapid response, good if you 5 it, but will likely need filtering and smoothing if you are more interested in meteorological humidity.
If the device caps output at 0—100 it makes it difficult to apply your own re-calibration near those limits.
This, the Si7021 and the SHT71 showed comparable errors overall.
Each of these three sensors showed advantages in one paramter or another, but given that I am only testing one example of each I cannot say if those are features of the device type or just my particular specimen.
My HTU21D exhibited good thermal stability and extremely low hysteresis.
Silicon Labs Si7021 I have nothing much specific to say about this, but I mean that in a good way.
In my tests it did exactly what it was supposed to.
The absolute errors were a little larger than advertised, but repeatability was good and the thermal dependence not too severe.
It is a nice compact and apparently robust unit, especially with the optional cover screen.
If the device caps output at 0—100 it makes it difficult to apply your own re-calibration near the limits.
This, the HTU21D and the SHT71 showed comparable errors overall.
My Si7021 is arguably the poorest of the three with larger thermal shifts and hysteresis, but given that I am only testing one example of each I cannot say if those are features of the device type or just my particular specimen.
Conclusion The BME280 delivered easily the best results.
The test is potentially unfair though given that they were brand new and are being compared against two-year old DHT22s and SHT71.
I have not had much luck with reliability of the DHT22s, but the Sensirion SHT71 has proven itself dependable over two years so far.
If you have comments or suggestions feel free to contact me.
Acknowledgments Though I designed and integrated the entire experiment, I must acknowledge the many open source projects, both software and hardware, that I used.
Drivers for other sensors were based on datasheets and sample code published by their respective manufacturers.
Almost vaguely related and possibly of interest is in the house.

Датчик температуры и влажности DHT22/AM2302

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