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AM2302 humidity and temperature sensor revival

I have an outside humidity and temperature sensor that uses the AM2302. Some month ago the humidity value it showed went up to 99% and sort of stayed there. Replaced it.

Now the new one, all of the sudden, same problem.

These are 'capacitive sensors', could not find anything wrong with my circuit and software (serial ink), so was wondering... What could cause a capacitive sensor to have a high humidity reading all of the sudden? Sure, leaking capacitor?

A magnifying glass showed what looks like a little on chip PCB with a gold electrode, and 2 tiny wires. But no air dielectricum, some other material.. Also a black blob, vertical.

One thing in the datasheet took my attention, had not noticed that before (datasheet is in Chinglish) something about a steady airstream:

[2] to achieve an order of 63% of the time required

Delphi Oracle (Pythia) would be proud of that statement....

Nowhere a reference to [2], so what did they mean? No 'airflow', I would have thought the storms of the past few days would have fixed that ...

*BULB* and indeed it was now at 98 % humidity, but the housing screens it a lot from sidewinds, and 100 % from rain.

So took it inside, blew at it strongly, back at normal value. Conductive? dust it must have been.

Good thing I kept the old one too.

Reply to
Jan Panteltje
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ayed there.

cuit and software (serial ink),

umidity reading all of the sudden?

d electrode, and 2 tiny wires.

(datasheet is in Chinglish)

have fixed that ...

a lot from sidewinds, and 100 % from rain.

Just mail it to me here in Florida. Reading 99% humidity, it will be accurate more than 99% of the time!!

Reply to
mpm

On a sunny day (Mon, 30 Oct 2017 04:14:02 -0700 (PDT)) it happened mpm wrote in :

..

I will fix that one the same way (I hope).

Buying new ones 2$85 a piece is cheaper than shipping from EU to US:

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What happened? in my days in Miami and Orlando it was much drier.. Flooding?

Reply to
Jan Panteltje
[snip]

Humidity? We're having a cloudy, over-cast day here... so the

...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 | "Those [of us] who dream by day are cognizant of many things which escape those who dream only by night" -Edgar Allan Poe

Reply to
Jim Thompson

Is it perhaps a condensation issue?

Pere

Reply to
o pere o

On a sunny day (Tue, 31 Oct 2017 09:17:20 +0100) it happened o pere o wrote in :

Yes, looks like that, I will have to design a better housing for the sensor. It went back to 99 % again last night for a moment. I also tried drying it by keeping it in the PC power supply fan output airflow, that worked even better than blowing at it.

What I think now is that, as I left the underside of the sensor housing open, warm water vapor rising up from the ground in the evening condenses against the colder sensor (2 meters up). An interesting problem. Heating the sensor is a no no as the temperature sensor is in the same chip.

Reply to
Jan Panteltje

Follow up. No, it seems now. Designed and build a new housing, and the sensor was still wrong, replaced it (again) and the new one is OK.

The only thing I could now come up with was 'lightning'. Next day after I put up the new one, lighting already happened and even the watchdog of the PIC did no longer revive the system. Power up down restored it this time. It seems both old sensors now have a calibration issue, are sort of OK at room temperature, but at lower temperatures those are now way off. Possibly an on chip EEPROM set by factory calibration did get erased? I now also added an extra big supply decoupling tantalum cap, against supply spikes.... Should have added diodes on the data line to the sensor too, but everything is now hot-glued and very difficult to open. If it goes wrong again I will include a power down sequence for the sensor (extra transistor), it is now POE.

Reply to
Jan Panteltje

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