Alt-BEAM Archive

Message #02638



To: beam beam@corp.sgi.com
From: Sean Rigter rigter@cafe.net
Date: Sun, 25 Apr 1999 12:33:33 -0700
Subject: [alt-beam] AQUASENSOR



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Hello everyone,

Introduction

Here is a simple but effective soil dehydration alarm circuit. Once the
threshold is adjusted for the specific plant and soil conditions, the
alarm will sound when it is "feeding" time.

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. 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. With
such low current consumption the battery should last for several years.
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. The two 10K
probe resistors are optional but may help protect the circuit against
static discharge etc. Without "field experience", I can not tell you
that this device will promote plant growth however if anyone builds it
and keeps careful records (as Steven Bolt has done for his plant
experiment) this could be an interesting science project.

While this project is not, strictly speaking, related to Beam robotics,
the circuit uses a same "freeformable" single chip design which is the
hallmark of so many Beam circuits.

A micro power valve is next perhaps using some air pressure in the water
bottle to propel the liquid uphill. Stay tuned!

How it works

The design uses soil resistance as the parameter for determining the
threshold of insufficient soil moisture content.
The resistance threshold detector circuit consists of a RC bridge phase
discriminator. One RC leg of the bridge is used as an adjustable
reference time constant (TC-ref) while the time constant of the other RC
leg is determined the same value capacitor but an unknown resistance in
the form of the soil moisture probe.

Under wet soil conditions the "unknown" resistance is a low value
(>20Kohm) and the TC is small compared to TC-ref. The threshold of soil
resistance is detected by applying a square wave to the bridge network
and by detecting which TC is the longest. The detector uses a two gates
from the 74HC132 schmitt NAND gate as an RS flipflop with both outputs
Set high when the applied voltage is 0V and on the rising edge of the
applied squarewave, the flipflop input connected to the leg with the
shorter TC is Reset (low output) while the leg with the longer TC
remains set. The first input to go high (shorter TC) together with the
cross-coupled high output from the other side causes the output of the
first side to Reset and thereby inhibits resetting the other side
because of the crosscoupled low output.

The 1Hz square wave clock is a conventional one gate Schmitt trigger
type and the 1KHz audio alarm clock drives a Piezo type speaker. The
audio alarm is held off with a 1N4448 diode connected to the reference
side of the flipflop as long as the soil resistance is lower than than
the reference resistance. When the soil dries out out increasing the
soil resistance and TC to a value greater than the reference TC, the
reference output is reset and the alarm is enabled and generating a
pulsing beeping sound.

While this is a simple application for this circuit I have found that
this design can also be used to detect changes in capacitance and then
behaves like a proximity detector. Adding a bias resistor to the
"unkown" reistance leg of the bridge can provide a micro power voltage
threshold detector and the list goes on.

This intriquing simple TC phase comparator has much potential for other
applications (including microcontrolers such as the PIC Stamp which also
use a similar single slope conversion TC/D and A/D interface) and I look
forward to seeing this circuit pop up in other Beam designs.

enjoy

wilf

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2639 Sun, 25 Apr 1999 12:34:29 -0700 [alt-beam] A cool program for BEAM newbies "beam@corp.sgi.com" zeroheroz
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I found a free down load that determines resistor values. I
think this would come in handy for those who are new to
electronics.
http://members.theglobe.com/n3ore/Downloads.htm

the name of the file is "colcode.exe". ........Darrell aka
ZeRo


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I found a free down load that determines resistor values.  I think
this would come in handy for those who are new to electronics.  http://members.theglobe.com/n3ore/Downloads.htmhttp://members.theglobe.com/n3ore/Downloads.htm">http://members.theglobe.com/n3ore/Downloads.htm HREF="">http://members.theglobe.com/n3ore/Downloads.htm">

the name of the file is "colcode.exe".   ........Darrell aka
ZeRo




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2640 Sun, 25 Apr 1999 23:56:48 +0200 [alt-beam] BEAM environment. "Jakub Pietracha"
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Last night I had a wision: a BEAM "plant" and BEAM bots feeding on it. The =
BEAM "plant" - something resambling the Green Thumb equiped with big solar =
cels and capacitors produces and stores power and diferent "species" of BEA=
M robos feed on it. Finding the plant is quite easily solvable (perhaps an =
IR LED on the "plant" and BEAM robots equiped with the instinct of IR-throp=
hizm instead of photo-thropizm) but geting the power from the "plant" to th=
e robot's is the problem. I thought of some kind of electrical contacts but=
the "plant" must serve several types of bots. Does anyone have any sugesti=
ons on solving the problem?
=

The construction of the robot must be also modified: =

- it has to store more power (maby an acumulator instead of a capacitor, or=
radical cut on the power consumption);
- it can't just stay near the plant and just feed (maybe some kind of explo=
re and hunger instincts). The hunger instinct could be a voltage detector -=
when the voltage drops below some point the hunger instinct overrides the =
explore instinct.

This type of environment could be an interesting place to observe. Just ima=
gine a turbot cravling twards the plant and "kiling" other bots just to get=
"food".

Jakub Pietracha
whraven@free.com.pl
=



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d of a =

capacitor, or radical cut on the power consumption);
- it can't just stay near the plant and just feed (mayb=
e some =

kind of explore and hunger instincts). The hunger instinct could be a volta=
ge =

detector - when the voltage drops below some point the hunger instinct over=
rides =

the explore instinct.

 

This type of environment could be an interesting place =
to =

observe. Just imagine a turbot cravling twards the plant and "kiling&q=
uot; =

other bots just to get "food".

 

Jakub Pietracha


 





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