GB2221036A

GB2221036A - Soil moisture alarm

Info

Publication number: GB2221036A
Application number: GB8906250A
Authority: GB
Inventors: David John Cross
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-03-22
Filing date: 1989-03-17
Publication date: 1990-01-24
Also published as: GB8806796D0; GB8906250D0

Abstract

Sensing means are situated in the soil of a plant and electrically connected to an alarm circuit enclosed within a housing. As shown the sensing means are in the form of an oscillator (TR1, TR2, TR6) driving two non-corrosive probes (XX) inserted in the soil and which when the resistance between them reaches a preset level, set by variable resistor (VR1), triggers a monostable circuit (TR3, TR5) which powers a piezo drive oscillator (PZ1) for a short time period. The resistance of the soil is sensed periodically in order to reduce the average power consumption of the circuit, thus, allowing the battery powering the circuit to last for a longer period than if the soil moisture were to be sensed continuously. <IMAGE>

Description

SOIL MOISTURE ALARM This invention relates to a soil moisture alarm comprising sensing means, an electrical circuit and an audible warning device.

Many householdersXdo not know when to water their houseplants, some watering their plants too often and others watering their plants too infrequently. Moisture indicators take the guesswork out of watering plants, ensuring that they are watered at the right time.

Most moisture indicators available at present on the market give a visual indication, some having an approximate scale relating to moisture level. One of the simplest moisture indicators relies on capilliary action to draw up water and darken a small window.

One major drawback with visual indicators is that the householder has to remember to look at the plant.

The present invention seeks to overcome this problem by giving audible indication when the plant requires water.

According to the present invention there is provided a battery powered soil moisture alarm comprising sensing means connected to an electrical circuit, said circuit controlling an audible device.

In one embodiment of the invention the moisture indicator incorporates two probes extending from the watertight enclosure, each probe being connected to a node of an electrical circuit housed inside said enclosure.

The electrical circuit comprises a battery powering an oscillator circuit with a very low duty cycle, said oscillator pulsing the power to the remainder of the electrical circuit of the soil moisture alarm, thus ensuring that the power consumption of the unit is minimal.

Preferably the enclosure is of a shape to facilitate easy insertion into the soil of a houseplant or similar, and the size such that the indicator will not disturb any roots of a houseplant.

If desired the top section of the enclosure is shaped to give the soil moisture indicator an aesthetic appeal.

If desired the sensing means comprises two concentric probes extending from the enclosure.

Preferably the audible indication takes the form of a repeating cycle of one short bleep followed by a relatively long silent period, and preferably the audible indication is unobstrusive and will not cause undue disturbance to the householder.

If desired the soil moisture sensitivity of the alarm unit may be adjusted for use with a variety of plants by means of a variable resistor incorporated in the electrical circuit.

If desired, power is provided by a solar cell arrangement, or in conjunction with a battery, thus, effecting a battery re-charge condition.

If preferred, an alternative alarm indication is realised by replacing both the piezo, PZ1, and the audible oscillator, comprising TR4 and associated components, by other indication means such as a flashing lamp circuit, or electro-mechanical buzzer circuit.

If desired, the condition of the battery is automatically indicated by means of a battery voltage sensing circuit, which, should the battery be in a low condition, will activate the sounding means in such a way as to be distinctive from the soil dryness indication.

If desired, the alarm sound, once activated, is disabled for a period of time by means of a switch or other controlling means.

One embodiment of the invention will now be described by way of reference to the accompanying drawings figure 1 schematically shows the electrical wiring diagram of one embodiment of the soil moisture alarm unit.

figure 2 shows the soil moisture alarm in use as it would appear in the soil.

Referring to figure 1, transistors TR1,2 and 6 form an oscillator of very low duty cycle, typically 0.02%, where TR6 provides for a fast charge up of capacitor C1. Capacitor C1 discharges slowly through the high resistance path formed by R1. The period of the oscillator is typically in the order of one minute, the on period being typically 10 ms, hence, the soil will have current flowing through it for approximately 10 ms. This has the effect of keeping the average current consumption of the circuit to a low level, and also preventing any appreciable build up of ions around the probes which could cause a sudden increase in the resistance of the soil which would be undesirable.

The monostable formed by TR3 and TR5 maintains an on period for transistor TR4 of approximately 0.5 seconds, thus producing an adequately long bleep of buzzer PZ1.

Referring to the figure 2 the soil moisture alarm, 1, is shown inserted into soil, 7, of plant pot, 6, surrounding a plant, 3. The enclosure, 2, of the circuit resembles a watering can and is designed to sit on the top of the soil. Apertures, 4 and 5, are provided in the enclosure, for the purpose of having adequate sound emission from the piezo electric transducer, and for adjustment of the moisture sensitivity respectively.

Two soil probes, X, are shown extending into the soil amongst the roots of the plant. The soil probes are connected to the circuit inside the enclosure.

Claims

1. A soil moisture alarm comprising sensing means connected to an electrical circuit, said circuit controlling an audible device.

2. A soil moisture alarm as claimed in claim 1 where unit incorporates a timer to periodically sense the soil thus reducing the power consumption of the unit.

3. A soil moisture alarm as claimed in any preceding claim where means are provided for adjusting the sensitivity of the unit so that it can be used for plants with different watering requirements.

4. A soil moisture alarm as claimed in any preceding claim where the audible indication is periodic thus reducing the power consumption of the unit and allowing the unit to operate in a manner that will not be obstrusive to the user.

5. A soil moisture alarm as claimed in any preceding claim where upon detection of soil dryness, a monostable circuit is triggered which in turn activates the sounding means for the duration that the output of the monostable remains active.

6 A soil moisture alarm as claimed in any preceding claim, wherein, the electrical circuit contained within the alarm is powered by a battery.

7. A soil moisture alarm as claimed in any preceding claim, wherein the signalling means comprises a piezo electric transducer.

8. A soil moisture alarm as claimed in any preceding claim, wherein the signalling means comprises a lamp.

9. A soil moisture alarm as claimed in any preceding claim, wherein the sensing means comprises of two non-corrosive probes.

10. A soil moisture alarm as claimed in any preceding claim, wherein the sensing means comprises two concentric probes.

11. A soil moisture alarm as claimed in any preceding claim where means are provided for manual or automatic indication of battery condition.

12. A soil moisture alarm as claimed in any preceding claim, wherein the alarm signal can be deactivated for a period of time once activated.

13. A soil moisture alarm as claimed in any preceding claim, wherein power to the soil moisture alarm, or means to recharge a battery, are provided by an arrangement incorporating a solar cell.

14. A soil moisture alarm substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.