I found a nifty idea to pulse pins on a homemade soil moisture probe (closely-spaced conductors in a plaster of Paris medium). I appreciate the importance of activating each conductor on the probe digitally instead of by steady DC. The Arduino code shows a 1 sec delay between alternate pulses to allow "capacitance effects to settle". One second seems intuitively a huge amount of time. I would have guessed that pulsing would have been at kHz or even more. Does anyone have any experience with this topic?
Thanks much!
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:-)
Pulse if you wish but the best way to use PWM and a little bit of hardware in terms of caps etc. This method with prevent capacitance effects and you can use most PICs to create te PWM and read the results. I have a set of damp sensors in my basement that have now been in operation for over two years.
Soil moisture would be measuring conductivity of the soil. If you use DC current then a couple of bad things happen like bubbles forming , plating, or destruction of the electrode. Low frequency AC allows the bubbles to escape and doesn't modify the electrode.
Old Leeds and Northrup Conductivity Analyzers used 60hz or 270hz.
Remember conductivity is related to temperature too. If you don't measure the temperature just be aware of where and what you are testing.
73
Mike
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mmotte:
Couldn't get your circuit from the PicAxe forum (requires you to join), so I don't know exactly what you're proposing. Unless you generate a bi-polar drive signal or capacitively couple the pulses into the probe, there will still be a DC component to the current with corresponding chance of electrolysis & probe corrosion.
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Not my circuit. I was only telling you about the caveats of conductivity measurement.
evanvennn's circuit is a water level controller. This is not the same application of measuring soil moisture. How would you measure soil conductivity through a capacitor? This water level circuit just measures the presence or absense of the pulses.
Just trying to help
mike
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I found a nifty idea to pulse pins on a homemade soil moisture probe (closely-spaced conductors in a plaster of Paris medium). I appreciate the importance of activating each conductor on the probe digitally instead of by steady DC. The Arduino code shows a 1 sec delay between alternate pulses to allow "capacitance effects to settle". One second seems intuitively a huge amount of time. I would have guessed that pulsing would have been at kHz or even more. Does anyone have any experience with this topic?
Thanks much!
:-)
Pulse if you wish but the best way to use PWM and a little bit of hardware in terms of caps etc. This method with prevent capacitance effects and you can use most PICs to create te PWM and read the results. I have a set of damp sensors in my basement that have now been in operation for over two years.
See the circuit in http://www.picaxeforum.co.uk/attachment.php?attachmentid=3173&d=1240775937 and my post http://www.google.co.uk/search?hl=en&q=Ken+Moffett+311209+and+MPep&meta=&rlz=1I7SKPT_en
Soil moisture would be measuring conductivity of the soil. If you use DC current then a couple of bad things happen like bubbles forming , plating, or destruction of the electrode. Low frequency AC allows the bubbles to escape and doesn't modify the electrode.
Old Leeds and Northrup Conductivity Analyzers used 60hz or 270hz.
Remember conductivity is related to temperature too. If you don't measure the temperature just be aware of where and what you are testing.
73
Mike
@mmotte. The circuit I have posted the link to prevents destruction of the probe. Just checked one of my probes… looks great after 2 years.
mmotte:
Couldn't get your circuit from the PicAxe forum (requires you to join), so I don't know exactly what you're proposing. Unless you generate a bi-polar drive signal or capacitively couple the pulses into the probe, there will still be a DC component to the current with corresponding chance of electrolysis & probe corrosion.
Here is the circuit, http://www.4shared.com/photo/OJ8ZNJpJ/WaterLevelPicaxe.html
A link to the User interface can be seen here http://www.youtube.com/watch?v=CzEob7sQs_Y I link the PIC to a very simple web service to generate the UI.
Not my circuit. I was only telling you about the caveats of conductivity measurement.
evanvennn's circuit is a water level controller. This is not the same application of measuring soil moisture. How would you measure soil conductivity through a capacitor? This water level circuit just measures the presence or absense of the pulses.
Just trying to help
mike
@motte. I agree with you too. I am trying to help also.
I aslo use the same circuit for soil moisture.
:-)
Thanks for all the comments and suggestions. I really appreciate the knowledge base here!