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Topic: Yet another Humidity and Temperature logger (Read 3204 times) previous topic - next topic

Anders 2009

:-)

Thanks!

Edge cases next and then the data logging shield.

Your support has been fantastic! Thanks again.

Anders


robtillaart

now you have humidity and temp you can calc the dewpoint.

Code: [Select]
// dewPoint function NOAA
// reference: http://wahiduddin.net/calc/density_algorithms.htm
double dewPoint(double celsius, double humidity)
{
        double A0= 373.15/(273.15 + celsius);
        double SUM = -7.90298 * (A0-1);
        SUM += 5.02808 * log10(A0);
        SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
        SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
        SUM += log10(1013.246);
        double VP = pow(10, SUM-3) * humidity;
        double T = log(VP/0.61078);   // temp var
        return (241.88 * T) / (17.558-T);
}

From - http://playground.arduino.cc/Main/DHT11Lib -
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

Nantonos


the EFS-10 humidity sensor. Here: http://www.produktinfo.conrad.com/datenblaetter/150000-174999/156545-da-01-en-Feuchtesensor_EFS10.pdf

I got the sensor as a present and really don't know so much about it other than it being sold by Conrad.de. It is the first time I use it and I can't say it was very easy. I am not used to generating AC signals to drive a sensor and then having to work out the impendance of it from the (volt) value you get from analogRead() didn't make it easier. Now add 2d-interpolation to that and everything gets a little too complex for a beginner like myself.

The LM335 is a common and easy-to-use temperaure sensor in a three-pin transistor like package. Didn't give me any trouble at all and pretty much worked the first time I hooked it up.


The EFS-10 does look a little complicated to use.

I ended up on this thread because I had just come across a humidity sensor and was considering making a humidity/temperature monitor. The one I found was Honeywell HIH-4000-0019 (datasheet) which has a simple 3-pin arrangement of Vcc, GND and analog output which is linearly related to relative humidity. (I found it on sale on eBay). I notice that temperature compensation is a simple quadratic, rather than requiring 2D interpolation.

Anders 2009


now you have humidity and temp you can calc the dewpoint.


Wow! Thanks! That might prove useful actually, both in terms of tracking mold conditions and in the balcony greenhouse I hope to build in a month or two.


robtillaart

dewpoint is important indoor, not only for mold but also for water in electronics :(

on that DHT11 page there is also a faster dewpint function '

I'll hear from you when your greenhouse is ready and you want to use RFID reader etc to identify the veggies ;)
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

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