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 never found a cause or have any suggestion for why they should fail to produce output in such a narrow range of humidity. Where blue dots scatter outside the shaded region it indicates a drift in the calibration as a function of temperature.

AM2302 Datasheet

All data collected, irrespective of temperature, are shown as blue dots. 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.

Looking at that the bivariate temperature: These plots show the error of each sensor as a function of humidity. The connection diagram for this sensor is shown below.

This means that with due regard to the errors already determined, hysteresis is not a signficant extra effect. Time response of the devices when exposed to a sudden upwards change in humidity. These same data are presented in more dayasheet in Figure 4. Plotted for comparison are values taken from the published literature. Though not discussed in detail on this satasheet, the effect of using the protective cover on the response speed has been investigated elsewhere.

Cyan data from O’Brien and yellow from Wexler The shaded grey region is the specified tolerance from the manufacturers’ datasheets. However, for all devices except the Si and AM the effect is small and the width of the envelope is not larger than the scatter of data points already observed. The large scatter of the blue points however show that the calibration degrades rapidly with varying temperature.


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.

AM Datasheet PDF –

It has been moved out into a separate document since rendering nine surfaces simultaneously proved an excessive load for some web browsers. It seems well made and has not yet shown any problems in well over two years of continuous operation. Readings were taken once every six seconds. Though equivalent for most normal use, the precise specification details do differ, most particularly in their speed of response. For all the other devices the numbers above are the maximum tolerances and most also offer better ‘typical’ specifications.

The sensor is also factory calibrated and hence easy to interface with other microcontrollers. Plots show temperature returned by each device compared to the average of all nine.

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. I discuss these together though they are distinct devices from two different manufacturers.

Each humidity level was held for twelve hours and the measured value logged every half hour. My conclusion was that is has virtually no impact at all. Plots showing the deviation of humidity values from the known reference value. Left panel shows data directly from the sensors.

First, unlike all the other devices tested it includes a barometer. My Si 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.

(PDF) AM2302 Datasheet download

A small adjustment to the internal calibration parameters could possibly bring this device to very nearly match the BME 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.


Over two years, three of the original six devices have failed. I am not sure.

The difference is so stark that it leads me to believe the sensing element is in some way fundamentally different from the other devices. 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. 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 the other sensors, where the slope of my data matches the slope of the reference data e. All the other sensors were multiplexed onto the I2C bus. The hysteresis curve traces a tight envelope and was highly repeatable on the two cycles performed.

If you are trying to interface DHT22 with Arduino Uno then there are ready made libraries for it which will give you a quick start.

Either way the performance of the sensor is same. The others all continue uneffected but values were only logged from this sensor when they were sensible. It was only by reading the internal serial numbers I was able to ascertain that. The shaded grey region is the specified tolerance from the manufactuers’ datasheets. The one-wire serial of the AM is retained making this a simple drop-in replacement. It is already included in the errors we have observed.

They seem to under-promise and over-deliver, so a priori I am not expecting problems outside the specified range. A ‘perfect’ sensor would be a featureless green plane at zero. It might be electrically identical. Hystersis was almost undetectable. Two complete cycles of the loop from wet to dry and back to wet were performed.