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[Reply #15 on:]

:-)

Thanks!

Edge cases next and then the data logging shield.

Your support has been fantastic! Thanks again.

Anders

[Reply #16 on:]

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

Code:

// 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 -

[Reply #17 on:]

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.

[Reply #18 on:]

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.

[Reply #19 on:]

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