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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AM2302 Datasheet PDF
It has been moved out into a separate document since rendering nine surfaces simultaneously proved an excessive load for some web browsers. They seem to under-promise and over-deliver, so a priori I am not expecting problems outside the specified range. The test is potentially unfair though given that they were brand new and are being compared against two-year old DHT22s and SHT Sensors were allowed to stabilise for a few hours with each solution. 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 Sis with the cover.
The devices are powered continuously, but the I2C IO lines are briefly connected to each device in turn. It worked again immediately once the humidity dropped.
All the other sensors were multiplexed onto the I2C bus. For most sensors the traces followed on rising and falling humidity are reasonably close together, showing little hysteresis bias. Second, it possibly works on an entirely different physical principle from the other sensors here. The hysteresis curve traces a tight envelope and was highly repeatable on the two cycles performed.
To show those differences in more detail I present plots for a single chemical as the temperature is systematically varied. My current supposition is that it uses a resistive film rather than a dstasheet film.
DHT22 Sensor Pinout, Specs, Equivalents, Circuit & Datasheet
The DHT22 Sensor is factory calibrated and outputs serial data and hence it is highly easy datawheet set it up. Notes on particular sensors: 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.
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. The membrane obscures ratasheet manufacturer’s mark on the left hand device, but reading the internal serial number shows it to be an Si 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.
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 absolute errors were a little larger than advertised, but repeatability was good and the thermal dependence not too severe. The large scatter of the blue points however show that the calibration degrades rapidly with varying temperature. Pin Identification and Configuration No: The DHT11 is clearly a different class of sensor with substantially lower specification and has been dropped from further investigation.
It is also the only model for which every device I own performs within specification.
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. 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.
In any case, they fulfill the manufacturer’s specified 1.
Currently I am attributing it to bad luck in my getting a couple of faulty devices rather than a systematic fault with dtasheet model. As far as I have been able to acertain, all the other devices are polymer capacitance hygrometers.
The Si 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 to better represent the wider prevailing conditions. Plots showing deviation of each device’s own temperature from the average of all nine, plotted as a function of temperature.
Figures 3 and 4 contain the same data plotted with different axes. At least the values are obviously wrong and an extra function was added to the microcontroller code to simply reject the bad data. Similarly the Sensirion SHT21 not included here also has a near identical specification and interface. At one sample per second values agreed with the polled operating mode where the device was put to sleep between readings.