AM (wired DHT22) temperature-humidity sensor . DHT11 datasheet (https ://)(in chinese, so see the DHT22 datasheet too!). AM digital temperature and humidity module is a digital output signal containing a calibrated temperature and humidity combined sensor. It uses a. AM Datasheet PDF Download – Digital temperature and humidity sensor, AM data sheet.

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I am experimenting the WebGL 3D surface adtasheet on this page and have had problems with very slow page loads in some browsers. 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, please refer to the previous write-ups. The devices now included are: The DHT11 is clearly a different class of sensor with substantially lower specification and has been dropped from further investigation. Comparison of the packaging of the various devices. 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.

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 dagasheet number shows it to be an Si Also commonly datasheeet as DHT Device E was selected as the best of the six I originally started with.

The AM is effectively the latest version of the AM with the addition of an option to communicate over I2C interface.

It is physically a little smaller, but with identical pin-out. The one-wire serial of the AM is retained making this a simple drop-in replacement. The AM appears to be the same but in a much smaller physical package and narrower pin pitch.

It might be electrically identical. There is some suggestion from the manufacturer’s web site that this might already be discontinued and replaced by AM I am not sure. The same device as was used in previous tests. I discuss these together though they are distinct devices from two different manufacturers.

In normal use they are interchangeable both in terms of specification and communications protocols and even have the same Datashheet address so are drop-in replacements for each other. Similarly the Sensirion SHT21 not included here also has a near identical specification and interface.

AM2302 Datasheet

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 dztasheet for which each manufacturer uses a slightly different format, detailed in their respective daatsheet.

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 ak2302. Though equivalent for most normal use, the precise specification details do differ, most particularly in their speed of response. 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 datasheeh the retailer had sent me HTU21s without the cover and Sis with the cover.

It was only by reading the internal serial aj2302 I was able to ascertain that. Though not discussed in detail on this page, the effect of using the protective cover on the response speed has been investigated elsewhere. 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. This device is a bit dataaheet. 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.

DHT22 Sensor Pinout, Specs, Equivalents, Circuit & Datasheet

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 BME 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 scanning electron micrographs of what is inside the BME 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 dataxheet to under-promise and over-deliver, so a priori I am not expecting problems outside the specified range.

Contrary 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 datasheeet 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 datashet the datasheet. Sm2302 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. Apparatus setup is essentially as previously described though a new board had to be built to hold nine devices inside the jars.

The AM 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 catasheet 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.

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, eleven saturated solutions 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.

  HP DX2000 PDF

Throughout the following plots you will notice the data for sensor G are a little more sparse than the others. 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 dtasheet 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.

It worked again immediately once the humidity dropped. Figures 3 and 4 contain the same data plotted with different axes. Figure 3 shows the actual relative datashete values measured and Figure 4 shows the deviations from a perfect calibration. Data obtained at other temperatures are shown in blue. Plots of the humidity values dahasheet 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. These same data are presented in more detail in Figure 4. Plots showing the deviation of humidity values from the known reference value.

Compare DHT22, AM, AM, AM, SHT71, HTU21D, Si, BME

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. Where blue dots scatter outside the shaded region it indicates a drift in the calibration as a function of temperature. The other six are new and this is their first test. The large scatter of the blue points however show that the ma2302 degrades rapidly with varying temperature.

AM2302 Datasheet PDF

As previously noted, this is my cherry-picked, best AM from a sample of six. Easily the best performers though are the BME 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.

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. They have remained fairly consistent over the six months between the two experiements. Figure 5 is sodium chloride. The smaller, round data points are the published reference values. Plotted for comparison are values taken from the published literature.

Blue data are from Greenspancyan data from O’Briengreen from Rockland and yellow, Wexler The thin black line is an ensemble fit to them all, weighting all equally. Cyan data from O’Brien and yellow from Wexler The thin black line is an equally weighted fit to both.

The BME 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.

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 Figure 4 are effectively cross sections through these surfaces.