Soil Temperature Sensor

Update 2011-09-05: I have created a new blog about electronics only – check it out here: Electronic measurements, NSLU2 and soil moisture sensor

Soil Temperature Sensor

This is my new homemade soil temperature sensor with a DS18S20 IC. The sensor is in the top of the picture. The left cable is coming from the NSLU2 computer and the right cable continues up to the air temperature sensor, which is also a DS18S20 IC. So now there are two IC’s on my 1-wire network using Cat5e Ethernet cable. The black tube on the left cable is just a collection of unused wires coming from the computer. These are required for other IC’s which will be added to the network later. The DS18S20 is glued onto a 20 x 20 cm (8 x 8 inch) aluminium plate to get good thermal contact to the soil.

Garden Air Temperature

Temperature graph for a day

I got my small NSLU2 computer up and running and it’s generating graphs from the garden. At the moment only the air temperature near the house is logged. The spikes in the graphs I believe is due to direct sunlight hitting the temperature sensor. I will build a shield over the sensor to prevent this. The sensor needs to be moved away from the house to get a more accurate reading.

The NSLU2 is running Debian on a 4 GB USB flash memory. I’m using a 1-wire system for the sensors together with the owfs software. rrdtool is used for generating graphs.

Here’s a script for generating the rrdtool database:
make_temps.sh

and a script for generating graphs:
update_temp.sh

Are you building your own temperature logging system? Using the NSLU2 computer, or owfs? Please leave a comment and tell a little about what your are working on.

New Soil Moisture Sensor

Soil Moisture Sensor

My Watermark soil moisture sensor arrived from the US the other day, and I’m currently working on connecting it to the small computer that will do the measurements and put them online on this website. As far as I know it works by measuring the electrical resistance in some material inside the sensor, and this will be converted to a number describing the moisture of the soil. The price was $32.