[ale] [On Topic / Off Thread] Interesting sensors - was: Re: [OT] how do I monitor the "weather" in my computer room

[agcarver+ale at acarver.net (Alex Carver)]

On 7/4/2013 11:33, Michael H. Warfield wrote:

> Now...  For those of us who have some other concerns.  :-)  I ran across
> this...
>
> http://www.amazon.com/sunkee-Hygrometer-Detection-Module-Moisture/dp/B00AYCNEKW/
>
> Now, that's intended for monitoring soil moisture in plants (and I
> certainly intend on using a couple for monitoring my landscaping and
> container gardens) but...  I've had several people ask me about
> monitoring for water in basements (flooding, water heaters, freezing
> pipes, condensation pumps, etc).  In the broadcast business we use to
> use similar sensors for monitoring our 1,000ft+ towers for icing and
> condensation conditions to control heaters on the towers - same
> principle.  If this sensor can tolerate being buried in soil conditions
> and survive, it can survive damn near anything else I can throw at it.
>

I like this sensor for the ease of use but one of the reviews on Amazon 
has the correct idea about ensuring that it is powered down and/or has 
the bias voltage polarity reversed every so often.  If not you'll end up 
with a completely oxidized PCB trace on the sensor probe (since they're 
using either tin-lead or silver solder to cover the traces from the 
looks of the photo.)

If you can, keep a lookout for capacitance style sensors.  The probe 
design for a capacitance sensor are waterproof (no direct electrical 
contact to the soil) to prevent short circuits.  It's capacitance tunes 
an oscillator and the shift in frequency tells you the moisture level.