2008 October - HappyFarming.com by Thomas Wagner Nielsen

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Soil Temperature Sensor

Oct 27

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.
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Garden Air Temperature

Oct 16

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.
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4 Responses to “Garden Air Temperature”
1. Paul Alfille said on October 17th, 2008 at 1:03 am
  
  Very impressive work! I am the author of owfs — can I feature your work on our website as an example application?
2. Thomas said on October 17th, 2008 at 12:35 pm
  
  @Paul: Sure, that would be great, thanks! I must say that owfs is easy to use once you know what to do. I’m looking forward to adding more 1-wire devices. I’m adding a soil temperature sensor, a moisture sensor and a rain collector to the system. I need to know when to plant them potatoes
3. Tuomas said on September 13th, 2009 at 11:32 am
  
  Hi!
  
  I have some difficulties to installa OWFS to my NSLU2 running debian lenny. Apt-get won’t find owfs and I’m not familiar to update packets list. Any ideas how to install OWFS?
4. Thomas W. said on September 15th, 2009 at 9:14 am
  
  @Tuomas: I think you have to download the source and compile it: http://sourceforge.net/projects/owfs/
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New Soil Moisture Sensor

Oct 4

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.
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2 Responses to “New Soil Moisture Sensor”
1. Paul Alfille said on October 17th, 2008 at 1:06 am
  
  This should work with owfs as well — though it’ll need calibration.
2. Thomas said on October 17th, 2008 at 12:43 pm
  
  @Paul: Yes I believe so. I’ll be connecting it to the Moisture Meter board from hobby-boards.com. And then I need to make a control system for automatic watering, but that should be possible with owfs too.
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