Humidity & Temperature Sensor

[ertansuluagac]

Hello everbody.
Is there a humidity & temperature sensor with precise working range that you can recommend?
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Es

[Ttelmah]

Too many possible parameters:

What humidity range?
What temperature range?.
What humidity range?.
What sort of environment?.
What gas?.
How 'accurate'?.
What speed?.

The DHT-22, can be quite acceptable for many applications. Quite slow,
but accurate for the price. Like all capacitive sensors they are not really
suitable for measuring low RH levels. Have quite good recovery from
dew saturation.
Absolute sensors are more reliable at high temperatures.
Resistive sensors have accuracy issues when the nature of the gas
involved changes.

You are going to need to narrow down what you actually 'want'.

[ertansuluagac]

I will use this sensor for irrigation in my garden. So its sensitivity is important.

Working Ranges

Working Voltage: 3.3-5 VDC
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Measurement Ranges
Humidity: 0-100% RH
Temp: -40 - 80 °C
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Precision:
Humidity: +/- %1 (Max %2) RH
Temp: <= +/- 0.5 °C
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Measurement Period: Less than 1 second
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Es

[temtronic]

Temperature is easy, DS18B20.... I'm using in my, er, WIFE'S, greenhouse. 12bits, <second. 32.2375*F as I type.

Humidity, get's tricky. I'm thinking you really mean soil moisture reading NOT air humidity.

All outdoor sensor's need to be shielded from wind, rain,etc. BUT still be 'open' for whatever their sensing.
Now depending on the garden size,shape, location, etc. you'll probably need 4-6 sensors. I can tell ,roughly, when the bushes shade the greenhouse from the sun, as temperature in GH drops a bit, sun moves , temp inside then goes back up...

[Gabriel]

Ive always though of this problem, since i grow alot of my own food.
The best idea ive thought of is using several DS18B20 some in air and some in the ground. Then write some code to treat the whole thing like a wet bulb Hygrometer. Haven't built it, probably won't, but with A LOT of calibration, it *should work?
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CCS PCM 5.078 & CCS PCH 5.093

[Ttelmah]

As others have said, for irrigation you really want to be measuring VWC
(Volumetric water content), not relative humidity.
In an enclosed space RH, will shift as the plants transpire during the day,
and has little if anything to do with how much water needs to be delivered.
Sensors like the VH400, measure the dielectric coefficient of the soil around
the probe. With suitable calibration this can be accurate, and reliable.

[ertansuluagac]

I will create an automated system. I want the rain sensor, temperature and humidity sensor to be of good quality. Also I want to do it by entering it with weekly daily time. My system is a drip system. The days and hours of my weekly irrigation system are certain. The system will automatically turn on and off at that time. Of course, I am searching for a solenoid valve suitable for this system. The system will also open and close the valve. If there is rain that day, the system will not operate automatically. If the temperature and humidity sensor is above the expected temperature and humidity, 2nd irrigation will be activated at intervals of 1 hour. This is the working structure
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Es

[kmp84]

Not sure if it is suitable for your project but you can also look at this sensor:
https://www.bosch-sensortec.com/products/environmental-sensors/humidity-sensors-bme280/

Also some helpful link:
http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html

Best Regards!

[Ttelmah]

The DHT22 I already mentioned, is as good. The RH is only +/-3%.
Generally to get much better than this you are going to need to calibrate
yourself, and this then brings the problem of what you use to do the
calibration....
The DHT manages +/-2% typical, and I don't know of any sensibly
priced sensor that manages better than this. Even units like the HTU31
only claim +/-2%.
The only ones better are where manufacturers calibrate them for you, and
then the prices are dozens of times higher.

[ertansuluagac]

Understood. Thank you very much.
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Es

[temtronic]

I've never considered monitoring humidity in the wife's 1/4 acre veggie garden or the 1/4 acre plot that 3 giant pumpkins are grown. I just water deep, on a regular basis,usually 3 or 4 days, depending on what Mother Nature supplies.
About 1150' of drip in 10-11 runs fed from 2000 gallon tank of rain water.
I was going to have a PIC control but it gets 'complicated'.. need flow sensors, one per feed, a few 'safety' switches, and temp sensors, oh yeah 'rain sensor', SSR for pump, sunrise/sunset calcs, wind speed, direction...
you can kinda get carried away with the project.....

[Ttelmah]

There is the old question, which is commonly 'misunderstood', which is the
difference between 'precision', and 'accuracy'.
He specifies a +/-1% 'precision', but I'm not sure here whether he really
means precision, or accuracy?.
Most of these sensors easily give +/-1% 'precision'. The DHT22, for example
has a resolution of 0.1% RH. However the 'accuracy' (so how closely the
figure actually matches the real measurement), is +/-2%.
You are actually 'better' to have a separate temperature sensor, and keep
the RH sensor somewhere that does not experience the worst temperature
fluctuations. RH sensors can give completely erroneous results when they
freeze (they internally have heating elements to avoid massive temperature
changes), having the sensor shielded from the Sun, and sheltered from
the worst of the cold, will improve the RH accuracy.

[temtronic]

Ssaw this today while coffee's being made...
https://www.banggood.com/Global-Version-Flora-4-In-1-Flower-Plant-Light-Temperature-Tester-Garden-Nutrient-Monitor-Tools-Kit-from-xiaoimi-youpin-p-1068369.html
Considering what's 'inside', to me it's a good value. I'm assuming it's some kind of bluetooth wireless. It'd be nice to be able to interface to a PIC 'master' to capture the data instead of some app on a smartphone, that probably links in to 'their' website.
Having 4-10 of them in a large garden would yield a lot of data !

[Ömer Faruk]

[Ttelmah]

Well, that is only a humidity sensor, so you are going to have to add
a separate temperature sensor.
The big 'downside' of it, is that it doesn't give you humidity directly. It
gives a change of capacitance. So you are going to have to turn this
into a humidity reading yourself. Either by changing this to frequency, and
then reading the frequency with the PIC, or by using the PIC itself as a
capacitance detector. In either case you will need careful circuit design
to minimise stray capacitance.