Alt-BEAM Archive
Message #02651
To: Sean Rigter rigter@cafe.net
From: Steven Bolt sbolt@xs4all.nl
Date: Mon, 26 Apr 1999 19:44:24 +0200 (CEST)
Subject: [alt-beam] Re: AQUASENSOR
On Sun, 25 Apr 1999, Sean Rigter wrote:
> It was inspired by Steven Bolt's Green Thumb project. The basic function
> of detecting dry soil conditions is there but in a smaller more compact
> circuit.
Glad to see the Thumb inspired a bit of tinkering :)
Nice design, too. Using a Piezo did cross my mind at the time, but
two LEDs - red to demand water, green to flash "all's fine" - were
preferred by the `user group'. A device which most of the time does
nothing might not be functioning. Given the two LEDs output
requirement, a second IC is hard to avoid.
> Used with a 1.5 AAA or button battery it draws a mere 5uA and
> 15 ua when the beeper sounds. It works down to 0.8V with a lower but
> still acceptable sound frequency and sound level. At which 1.0V, the
> current consumption is only 0.5uA and 3 uA when the beeper sounds.
So a small solar panel would do very well. Why use a battery?
> The threshold is quite stable over the operating voltage and temperature
> range because of the closely matched characteristics of the "same chip"
> CMOS inputs which largely cancel out temperature and voltage effects.
> This is a small improvement on the orignial since Steven Bolt uses two
> chips with different input thresholds and this may make the threshold
> setting sensitive to voltage and temeperature variations.
True (though not noticeable in this application). Moreover, using a
74HC132 to make both the S/R flipflop and the generators is a very
nice idea.
> The two 10K probe resistors are optional but may help protect the
> circuit against static discharge etc.
The larger caps of the Thumb help, and once the sensor is in the
soil, static charges can't build up.
> A micro power valve is next perhaps using some air pressure in the water
> bottle to propel the liquid uphill. Stay tuned!
Looking forward to that valve!
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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