Soil moisture sensor
As mentioned in the Talk i am working on capacitive soil moisture sensing.
I read lots of stuff on different sites about capacitive vs. resistive measurements and decided to try something like this one (germann info only) which is already used in this project (german info again, schematics and more over here).
Sensor and PCB
Dietmar Weisser was so nice to send me an improved version of his sensor as eagle files.
Eagle BRD
schematic
The sensor needs to be enclosed waterproof so not moisture gets into direct contact with the sensor plates!
The sensor is designed to be connected to a timer/counter input and "count" the frequency for 10 or 100ms. That frequency should directly relate to the soil moisture.
Connection Options
As jcw pointed out in the talk one sensor could be directly connected to a JeeNode:
The PD5 pin can be used as counter inout for timer 1 (T1), this is the DIO pin of port 2. I'd reduce the measuring time to 10 milliseconds, though. I.e. wait for milli change, reset timer 1, wait for 10 ms, then read out timer 1.
Since i do not want to power the sensor all the time and soil moisture drifts very slowly power could be controlled, too - again, jcw:
You could try powering each sensor from a spare DIO/AIO pin configured as output, then turn on "power" for only one of them at a time. To get the output to pin DIO2, connect each output via a diode as pull-down, and enable the pull-up on the DIO2 input. That essentially creates an AND gate, but since only one of the sensors pulls down, you'll be feeding just that one pulse train to the DIO2 pin (i.e. PD5). This only requires a few diodes. It may or may not work, you'll have to experiment.
Intelligent Sensor
More intelligent or "autarkic" sensors sound like a better idea. Via I2C or another bus sytem and protocol multiple sensors could be connected to one JeeNode.
My next step is to find out what components qualify to "complete" the sensor. Maybe a Tiny13 or so - i have no idea yet, to be honest ;)
(From TikiWiki - Created by MarvinGS)
