Using a LDR (light dependent resistor) and DHT11 temp/humidity sensors

I got my hands on a LDR yesterday and figured that it will make a nice addition to a greenhouse monitoring project that will pick up light intensity, air temperature and humidity plus soil moisture and send that information to emoncms on regular basis. I still don’t have the soil moisture measuring circuit, so I  created the other components.

For measuring light intensity I use this basic schematic:

.. and it materialized in this small plug:

The idea is to power it with a digital pin so that battery is saved. I also have a DHT11 temperature and humidity sensor, this is extremely cheap (~$4 including shipping)  sensor that is barely good for anything, but hey worth giving it a try. The problem is that it measures integer values only plus humidity readings are quite off. I guess I will have to add calibration to match its readings with another more accurate room air humidity sensor. The sensor plugs directly in the dedicated socket, small code changes are necessary because the power pin is the middle one on this sensor.

So here is my setup so far

Here is my test code, nothing fancy. I used this DHT11 code: to read the DHT11


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  1. Pingback: DIY soil moisture sensor project | Martin's corner on the web

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