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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Most of the others seem comparable to each other except the Si which is the one major outlier. The right hand device without the white protective cover is an HTU21D.
The duration of each host signal is explained in the datasheet, with neat steps and illustrative timing diagrams. The DHT22 is a commonly used Temperature and humidity sensor. It is true though that all values will be slightly biases one way or the other as conditions change. As expected, all sensors do show the tendency to read systematically high when the humidity is decreasing and read low when humidity is rising. 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.
The reference calibration sources are the same as before, eleven saturated solutions and distilled water. Blue data are from Greenspancyan data from O’Briengreen from Rockland and yellow, Wexler Repeatability at a fixed humidity is very good.
The data scatter is small and the calibration error is linear in both the humidity and temperature directions. The hysteresis curve traces a tight envelope and was am2032 repeatable on the two cycles performed. For the other sensors, where the slope of my data matches the slope of the reference data e.
The word is derived from ancient greek for ‘lagging behind’. Within the data obtained here, the BME is the undisputed winner.
Finally, if a sensor is to be used to measure humidity under a range of varying temperatures a full bivariate calibration is required. Again I wonder if this suggests fundamentally different sensor technology from the other devices. The others all continue uneffected but values were only logged from this sensor when they were sensible.
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. It might be electrically identical.
Currently I am operating on a am23022 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. The connection diagram for this sensor is shown below.
DHT22 Sensor Pinout, Specs, Equivalents, Circuit & Datasheet
There is some suggestion from the manufacturer’s web site that this might already be discontinued and replaced by AM Figure 11 shows an apparent scatter but replotting temperature errors as a function of humidity Figure 12 shows a tight correlation with very little dispersion.
The other six are new and this is their first test. Here I have added five new devices meaning this test now covers most commonly available low-cost digital hygrometers.
Plotted for comparison datasheet values taken from the published literature. The shaded grey region is the specified tolerance from the manufacturers’ datasheets. 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.
AM Datasheet PDF –
As previously noted, this is my cherry-picked, best AM from a sample of six. Though not discussed in detail on this page, the effect of using the protective cover on the response speed has been investigated elsewhere. Datashet E was selected as the best of the six I originally started with. The thin black line is ma2302 ensemble fit to them all, weighting all equally. The sensor itself is the small square component in the top right of each board.
(PDF) AM2302 Datasheet download
In those images, the lower die datasheeet 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.
In the right hand panel the lag has been arbitrarily removed and the values datasheett in order to compare the intrinsic response speed of the sensor elements.
Plots showing deviation of each device’s own temperature from the average of all nine, plotted as a function of temperature.