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AM2302 stopped working
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AM2302 stopped working

by khtodd on Mon Sep 10, 2018 9:26 am

hi - amongst other things, I purchased an AM2302 humidity sensor from Adafruit about a half year ago. I have it working in an indoor garden tent with an Arduino Uno. It had been working fine for months, but all of a sudden, the readings started becoming all wrong. Now, it only puts out a reading of 1%, regardless of the true humidity inside the tent.

Is there a way to fix or recalibrate the sensor, or does it need replacement? What is the typical life expectancy of this item?

Thank you.

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Re: AM2302 stopped working

by adafruit_support_bill on Mon Sep 10, 2018 10:09 am

Do you still get reasonable temperature readings, or are they also wrong?

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Re: AM2302 stopped working

by khtodd on Mon Sep 10, 2018 10:11 am

the temperature readings seem ok

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Re: AM2302 stopped working

by adafruit_support_bill on Mon Sep 10, 2018 10:23 am

That would rule out a communication problem.

All sensors have a finite lifetime. But humidity sensors tend to be more fragile than most. Repeated exposure to very high or low humidity extremes - especially condensing conditions will shorten the sensor's lifetime. The AM2302 datasheet also warns about exposure to chemical vapors, strong light and/or UV.

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Re: AM2302 stopped working

by khtodd on Mon Sep 10, 2018 12:08 pm

Thanks. I guess I'll have to replace it - there's no way to correct the humidity sensor once it has a problem, right?

The sensor does get some extreme conditions - no chemical vapor, and it's out of the strong light. Daytime humidity is usually around 50-60%, but it sees about 92% humidity for 3 hours each night.

Is there another sensor that would be more robust that would take that kind of environment better?

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Re: AM2302 stopped working

by adafruit_support_bill on Mon Sep 10, 2018 12:43 pm

there's no way to correct the humidity sensor once it has a problem, right?

Often after exposure to extremes, capacitive polymer sensors such as the AM2302 will give skewed readings for a while, but slowly recover. But repeated exposure will accelerate aging and if it has been giving you bad readings consistently for a few days, then it is probably not recoverable.

Is there another sensor that would be more robust that would take that kind of environment better?

There are industrial humidity sensors available from companies such as Omega Engineering. But they are in an entirely different price range.

We do have a couple of sensors that incorporate PTFE filters to better protect the sensor.
https://www.adafruit.com/product/1899
https://www.adafruit.com/product/2857

The Bosch sensors also seem to be a bit more robust than most.
https://www.adafruit.com/product/2652

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Re: AM2302 stopped working

by khtodd on Sat Sep 22, 2018 8:29 am

As an inexpensive temporary stop gap (while I decide which way to go more permanently), I replaced the sensor with another one of the same, but now there is a new problem.

It reads fine for a while, but then, randomly, it will start giving nan for both temp and humidity levels. Once it starts this, it will not give a true reading again. But, if I restart the arduino, it reverts to providing good readings again. By "for a while" I mean a few hours at least to up to a day or so.

I take readings every 3 seconds.

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Re: AM2302 stopped working

by adafruit_support_bill on Sat Sep 22, 2018 9:21 am

That is strange behavior. Please post some photos showing how you have everything hooked together.

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Re: AM2302 stopped working

by khtodd on Mon Oct 01, 2018 8:42 am

Sorry for the delay. I have attached a photo of the sensor and how it is attached. There are #20AWG wires that are about 5 feet long that lead to the Arduino. The extension wires are crimped to the sensor's leads using industrial blind end connectors.

What I find is so weird is that the sensor will work for a long time, so far about 8 hours at minimum, up to a few days, before it gives nan output on both temp and humidity. But resetting the Arduino (without touching any leads) will get the sensor to work properly again.

I appreciate your thoughts.
20180930_192708-1.jpg
20180930_192708-1.jpg (620.11 KiB) Viewed 51 times

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Re: AM2302 stopped working

by adafruit_support_bill on Mon Oct 01, 2018 9:17 am

Not sure what those other wires are. But with unshielded wires running roughly in parallel in close proximity, I suspect you may be getting some inductively coupled noise.

Try routing your sensor wires well away from the other wiring.

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Re: AM2302 stopped working

by khtodd on Mon Oct 01, 2018 9:31 am

I'll try that, but it brings up a question - the old sensor was mounted and wired in exactly the same way and never had a problem until the humidity sensor went bad. The other wires lead from the Arduino outputs to new adafruit Powerswitch Tails to turn lights/fans off a few times a day... so the other wires are basically running 5VDC and only switch like once a day. The old sensor never gave a nan response and it was running on the same code, wired in the same way.

This still doesn't answer the question as to why the sensor may work fine for 3 consecutive days, and then stop working at a random time, and then work fine again if I cycle the power to it.

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Re: AM2302 stopped working

by adafruit_support_bill on Mon Oct 01, 2018 9:43 am

The other wires lead from the Arduino outputs to new adafruit Powerswitch Tails to turn lights/fans off a few times a day.

A powerswitch tail has a relay. And relays have two sources of EMI. One is the inductive spike that occurs when the coil is de-energized. The other is the spark gap across the contacts as they open. Also, fans are motors which are prolific sources of EMI - particularly when starting and stopping.
so the other wires are basically running 5VDC

As well as acting as broadcast antennae for the EMI.

This still doesn't answer the question as to why the sensor may work fine for 3 consecutive days, and then stop working at a random time, and then work fine again if I cycle the power to it.

We don't know the internal architecture of the sensor chip. But it is not unusual for a noise spike to put a device into a random state that can only be cured by a power cycle.

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Re: AM2302 stopped working

by GSAIDAH on Tue Oct 16, 2018 11:58 pm

Hi,
I purchased an am2302 wired (ADA393) and a DHT22 (ADA385) from Amazon and have similar problem with both. No reading after few hours.
I am connecting them to 2 different ESP12F with a 4.7k ohms between the 3.3v and data pin as a pullup.
I use those ESP12F with DS18b20 without any problem at all for a very long time.
I tried everything I can think of to figure out why they stop working, but could not figure it out.
I tried to use different cables from 3 to 6 feet, shielded or not, but have the same issue.
I tried different power supplies, I tried to isolate them from anything close to them.
I tried to do a soft reboot every few hours, but that does not reset the sensors. They need a hard reset.
They will work for a while, 8 to 12 hours and then stop working until I reset the power or just disconnect the sensor and plug it back in.
They are being tested in my garage in southern california without being exposed to extreme temperature or humidity.
I can send pictures and diagram of my setup if you need it.
Could you suggest anything else for me to try?
Thank you,
George

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Re: AM2302 stopped working

by GSAIDAH on Wed Oct 17, 2018 12:06 am

I forgot to mention that I have 2 wired and one DHT22 connected in the same area and they will not stop at the same time. Some stop after 8 to 10 hours and other may last 14 to 20 hours, but all of them stop working eventually.
Thanks,
George

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