Alt-BEAM Archive
Message #02685
To: Steven Bolt sbolt@xs4all.nl, beam beam@corp.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Tue, 27 Apr 1999 07:23:25 -0700
Subject: [alt-beam] Re: AQUASENSOR
Thanks for testing my "paper" design Steven,
You are correct in your analysis. I also had a chance to test the
circuit and found much the same: the voltage must be a 3V lithium
battery or equal to drive the LEDs. The current limiting resistor is not
required, the time constant of the pulse circuit can be reduced to 30ms
and the resultant current is about 250-300uA. If you must periodically
have to look at the LEDs you could also stick you "real" thumb in the
soil and get a "feel" of the moisture content. So in retrospect, the
original the ultra low power, 1.5V battery powered, "set and forget"
piezo design makes more sense for less attentive gardeners who need to
be triggered into action by the audible low water alarm. WARNING: there
is some risk to the user that over time this PIEZO AQUALARM will produce
a "conditioned" response with an urge to "water" something every time
you hear a beeping sound 8^)
enjoy
wilf
Steven Bolt wrote:
>
> On Mon, 26 Apr 1999, Wilf Rigter wrote:
>
> > Here's a single chip LED version. The LEDs must be high efficiency type.
> > With 3% duty cycle the average current is about 200 uA.
>
> Very nice, Wilf! I didn't think of that one :)
>
> And with the LED pulse width set to the Thumb value (by using 4M7
> instead of 10M resistors), your solution does not consume
> significantly more current than the Thumb.
>
> One remark though: The Vf of my 2mA LEDs is too high for operation
> at 1.5V. I needed > 2V to get visible flashing, and my catalogs
> fail to mention low-current LEDs with a Vf that would allow a
> single cell power supply.
>
> Best,
>
> Steve
>
> Btw: Why don't you put your designs and descriptions up on Zoz'
> Heretics pages:
>
> Linkname: BEAM Heretics Site
> URL: http://www.serve.com/heretics/
>
> Under the "electronics" heading? That would give them some
> well-deserved Webspace.
>
> ----------------------------------------------------------------------
> # sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
> ----------------------------------------------------------------------
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