ELECTRONIC MOISTURE-METER WITH ALARM

HUMIDIMETRE ELECTRONIQUE A ALARME

English Abstract

The invention consists of a portable instrument, of a very high accuracy,
which measures the soil moisture and which can be calibrated (gauged) for the
use in the most different conditions, in function of necessities.
It is a multifunctional gauge of a compact construction very well adapted
to the purpose it was conceived for.
In order to measure the soil moisture, the gauge uses the proportionality
between the soil humidity contents and its electric conductivity. The
information is displayed by a series of LED-s. In contrast with the use of a
needled pointer, this mode of displaying gives a great endurance to the gauge.
When it is switched to the ~ALARM~ mode of functioning, the gauge detects
any decrease of the soil moisture level under a preset threshold, depending on
the type of plant signaling either optically or acoustically, at choice.
The gauge uses a measuring probe of an original conception, made of
conducting tracks specially conceived for this measurement.

Claims

CLAIMS
1. The use of a probe made of printed circuit boards.
2. The use of a probe as explained at point 1 with conducting tracks (drawn in
a specific form) as a moisture sensor.
3. The probe described in point 1 and 2 of the Claims is detachable being
connected to the gauge by a connector.
4. The probes described in the above-mentioned claims (1, 2, 3) have different
sizes.
5. The construction of a probe in function of the plant-pot size.
6. The selection of the plant type done by means of the switch S1.
7. Selection of an alarm threshold by using a switch (S1).
8. The display of the soil moisture (by LED-s) at request by pushing a button.
9. The soil moisture is displayed by means of a series of LED-s suggestively
colored: yellow for dry soil, green for normal humidity and red when the soil
contents water in excess.
10. The achievement of an alarm in case of low moisture content of the soil.
The alarm is automatically released when the moisture-meter detects the
inferior limit of accepted moisture content. This threshold limit can be
selected by the switch S1.
11. The alarm can be launched by either optical or acoustical signals, at choice,
signaling the decrease of the soil moisture content under a preset
threshold.
12. The use of the piezoelectric sensor for the acoustic alarm and the LED for
the optical alarm.
13. The construction of a moisture-meter using the proportionality relation
between the soil humidity and its electrical conductivity.

Description

CA 022l9474 l997-l2-24
Detailed descrip~ion
The functioning mad~ of the Al~rm C~rcuit
The soil conductivity is measure~ between termina~s 1 and ~ of the
measu-rin~ et~e~rode ~Fig. 4).
The alarm cireuit compnses ~wo integrat~d eircliits of LM 555 ~ype,
transistors Ql, Q2. a ~ and the alferent passiYe components.
The t~ase of the dar~ington transistor is potarized ~y Resistors Rl and R2 and
also by the soil resistor measured between electrodes 1 and 2, noted Rl 2 This
one is varying in function of the soil wetness. The sensitivity of the input
buffer can be adjusted by the switch S1 connected to resisto~s Rl and R2: if thevalue of R~ 2 increases over a certain threshold, selected by 5" the darlington
transistor ~Q1~Q2) starts condueting and its cottector current is ctosed ~y
resistors R3, R ,. ~he v~ttage ~merginy at the terminals of resistor R3 connected
between the base ~8) and em~tter ~E~ an~ transistor ~, opens this transistor
which is feeding the integrated circuit C11 - operating as a timer - by resistorR7.
The integrated ~ircuit Ct1 has the pin t conneeted to the m~ss, pin 2
connected to pin 6 and to ~he mass by capaeitor Cl. Between pins 6 and 7 i t i ~ptared the resistor Rs which, together with resistor R6 connected between pins
7 and 3, determine the oscillation ~1equei7cy and ~he report pulseJpause of th
output vott~ge picked up by pin 3. This vottage is used to controt, l~y resistorRBI the openin~ of transistor ~, whi~h has in collector, as a charge the LED 5
s~ries-connected to resistor R, l, wltich is connected to tlle mass. T~is one w i I t
start blinking when the soil l~ecomes too dry.
The second integrate-d circuit of ~ype LM S55 use~ as soun~ generator for
the acoustic alarm is fed by switch S2. Its osciilation fr~quency is determined
by resistor Rg ~connect~ between pin 7 of the integrated circuit and its
feeding source), resistor Rto (connected between pins 7 and 6 of the integrated
circuit) and capacitor C2 ~connected between pins 2 with 6 and the mass):
fau~o = 1 ~ 2000Hz
To the outp~t of the sound generator made up ~y this integrated circuit ~pin
3) is connected an acoustic sensor, a piezoelectric sensor.

CA 02219474 1997-12-24
~ he s~and-by consumption v~ the alarm buffer is very reduced ~approx. 4 ~A)
determined only by ~he polarization resistançe of the base of Q" 0~ transistors
done by resistors R1, Rz and switch S1. When the alarm is launched, all the other
components will be fed by the electronic switch made with transistor Q~,
The very reduced current contained between the measurement electrodes 1
and Z slackens down the corrosion.
It is to note that;
R 1. 2 = p * ~
where p is in function of the soil moisture
and
e
2 s is given by the geometry of the measurement probe
~L
The functionn~ng mode o~ theMo~sture-Meter
The moisture-meter measures the soil moisture using the proportionality
relation between the moisture of the soil and its electric conductivity
measured ~etween electrodes ~ and 3 of the measurement probe. The moisture
content of the soil is indicated by 4 L~D-s (3 green ones indicating the normal
moisture content and a red one ~ndic~ting an excessive soil moisture~.
The moisture-meter is fed by S3 knob only when we want to effectuate the
humidity reading. This way we diminish both the battery current consumption
and the corrosion of the measurement probe, The integrated circuit LM 339
~quad comparator~ controls the 4 LE~ connected ~y res~stors R~s~ P~20, R21~ R22
to the 9V voltage of the battery.
The "t"lnpUts of ~he 4 comparators are all together connected to ele~trode
3 of the measurement probe.

CA 022l9474 l997-l2-24
Th~ YQ!t~Qe~+ = ~ 3f~1Z* ~-~G
We hal,re c~?oserl as ~hresh~lds:
R1,3 t ~K 50K t ~K 2K
-> v~ 4;5V ~V Q ~V Q,175
Green Red
The ~ nputs of the omparators ~re connected to the eference Yo~tages
obtained by the ch~n~ ~f r~s~o~ R13, ~14~ R~ 16~ R17~ R18 ~S ~ WS- pin 1
between R, 3 and R, 4, pin 8 between R14 and R, ~;, pin 4 between R, ~ and R, 6 and pin
6 between Rl6 ~nd R17. The ~uad c~n~,~al~tor is ~ed by pin 3 only w~en pressing
~3 ~utton during the measuremen~ process.
The pin 1~ o~ th~ inte~rat~ circ~it ~t 33~ is co~ecte~ to ~c m~ss, ~n~
the csmparatorsl outputs ~p}ns 1, Z~ 14~ 13~ are connect~d res~ectively to
LE0-s 4, 3, ~, ~ whic~ in~cat~ m~ist~fr~ c~nt~nt o~ ~h~ SOlt~
~s~
I max = ~U~UA ~ ~ r r/ Rl ~ = p * S = ~l 2 ~l le tn thP nr~be s
~ring the ~~ $ ' ' 2 ~ symmatric ~onstruc;ion.
me~suremPnt ~ Consequentiy, the posi~ion in which ~hé probe
~when S~ is ~ ~s oonneeted to ~he e~nneetor has no
pressed3 i ~ impor~ance. We may use v~riou~ ~ne~ure!nent
~.CY probes of different iengths on condition to
respect the report s by mean~ ~f which the moi~ture-meter has been
standard~ze~. -

Representative Drawing