GB2320572A

GB2320572A - Plant moisture detector

Info

Publication number: GB2320572A
Application number: GB9626323A
Authority: GB
Inventors: Peter Hulme
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-12-19
Filing date: 1996-12-19
Publication date: 1998-06-24
Also published as: GB9626323D0

Abstract

A detector is in the form of a sheet (1) of plastics material and is powered by a solar cell (2). An oscillator 5 has an output determined by the capacitance or resistance between two divergent strips (6) and (7) which is in turn determined, inter alia, by the moisture content of soil in which the detector is inserted. An LCD display (3) varies with the oscillator output to indicate whether a plant requires watering.

Description

PLANT MOISTURE DETECTOR This invention relates to a plant moisture detector.

The nurturing of plants can be a rewarding hobby or commercial enterprise. To grow successfully, and strongly, however, plants require the correct amount of water. They should neither be over-watered nor underwatered.

Devices are presently available which can measure the degree of moisture of a soil and thereby indicate whether a plant in the soil needs watering.

However, these type of detectors generally require batteries and use light emitting diodes (LEDs) to display moisture level. The incorporation of batteries into a design is disadvantageous in that it leads to a bulky end product and either has a limited life or requires the batteries to be changed on a regular basis. For these reasons, such designs have not yet proved commercially successful in the United Kingdom.

It is an object of the present invention to provide an improved plant moisture detector.

According to the present invention there is provided a solar powered plant moisture detector.

According to the present invention in a second aspect there is provided a plant moisture detector comprising a solar cell and a moisture detector means.

The plant moisture detector is embodied as the type which is partly inserted into soil around the plant, which is in a pot or planted in a bed for example, and measures the moisture of the soil in the vicinity of the plant.

Preferably, the moisture detector comprises an oscillator and a pair of electrically conductive probe strips connected to the oscillator, such that the oscillator is controlled by the capacitance or resistance between the two strips to alter the display on a liquid crystal display.

In one embodiment, the probe strips are preferably arranged to diverge from one another, such that the gap between them is greater towards the tip of the detector (i.e. away from the oscillator), so that the capacitance between them varies along their length and thereby sensitivity to moisture is varied as the detector is pushed into the soil to be tested.

Alternatively, the strips may be substantially parallel, so that the resistance between them, that is the resistance of the moist soil, varies as they are both inserted into the soil.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing in which: Figure 1 shows a plant moisture detector; Figure 2 shows a plant moisture detector in situ; Figure 3 shows schematically the operation of the plant moisture detector; Figure 4 shows schematically a further embodiment of plant moisture detector; and Figure 5 shows schematically a yet further embodiment of plant moisture detector.

Referring to Figure 1, a plant moisture detector is generally in the form of a relatively thin, preferably flexible, sheet 1 which may be of a plastics material suitable for encapsulating electronic circuitry. The plastics material may be of the type such as polycarbonate used for Smartcard manufacture. Alternatively, the device may have a substrate of any other material.

The detector 1 includes one or more solar cells 2 arranged to collect sunlight and to generate electricity therefrom. The solar cell may be of a similar type to those found in some calculators for example. The solar cell powers a liquid crystal display (LCD) indicator 3 which in the example shown, displays an iconic representation (4) of a watering can. Any other symbol may of course be displayed, as may alphanumeric characters or any other display. The LCD indicator is driven by a semi-conductor oscillator forming part of an electronic circuit typically in the form of a chip 5. When the oscillator is operational, the LCD area goes dark to display the icon. When the oscillator is not operated, or is not operated at a sufficient frequency or voltage, then the icon 4 is not displayed. Oscillator 5 is controlled by the capacitance or resistance between two probe strips 6,7 which are preferably surface mounted on the body of the detector. The probes are mounted such that they diverge away from chip 5. The gap between them is therefore greater towards the tip of the detector (i.e.

away from chip 5) such that their sensitivity to moisture is greater the further the detector is pushed into the soil to be tested. This is because the output signal from the probes are which is determined by the capacitance or resistance between them, would clearly increase, for uniform conditions, as the level to be measured approaches the chip 5 and thereby the distance between the strips reduces. It is thereby possible to set the oscillator so that when a particular moisture level is detected the indicator 4 changes colour to show that there is insufficient moisture and that the plant needs watering.

The probes may be of a resistive material, or may have a coating or be made of a material which resists oxidation or attack by substances normally encountered in the soil, such as alkalis, acids or various chemicals of other compositions used to aid and encourage growth, as well as pesticides, fungicides and so on.

Figure 2 shows a device 1 in situ, showing the device pushed a distance b into the soil next to a plant 8. Since different plants required different levels of water, by moving the device 1 up or down when the plant is correctly watered a correct level can be determined so that the device can be left in place and, as soon as the moisture level in the soil reduces to that at which watering of the plant is advisable, the display 4 on the LCD indicator 3 changes.

In a variation, the detector is not actually affected by the depth to which it is pushed into the soil, but instead shows the level of moisture on a graduated display for example. The user can then tell when it is nearly time to water the plant. In further variations, the need for water may be signalled by the emission of an audible or a visual warning or a combination of these.

This may be achieved by connecting visual warning devices, such as LCDs, or small low power sounders to the electronic chip 5.

Solar cells, of the type which are currently cheaply available, are sensitive to a reasonably low level of ambient light and so the device should be able to keep powered over most daylight conditions. In some embodiments, a rechargeable power source, charged by the solar cell, may be included or a small battery could be included for back-up use.

The detector may be embodied as a sheet, e.g. of plastics material, glass fibre material or other material suitable to bear the components durably, and is waterresistant, at least when adapted for external use. It may be roughly the size and shape of the type of information tag commonly sold with a plant, giving watering details etc, and may indeed bear these details on one of its faces. It may alternatively be credit card shaped and/or sized for example, but could be other shapes or sizes. It may alternatively be in the form of an elongate rod, e.g. cylindrical, so that it is pen-shaped in one embodiment. Other shapes and sizes may be used.

The detector may even be in the shape of a watering can for example.

The detector may also bear advertising material, printed or otherwise affixed to its surface. This is particularly advantageous where the detector is in sheetlike form as it may display advertising material on one or both sides. If produced cheaply enough, the detector may then be used for promotional purposes.

Figure 3 shows schematically the embodiment of Figure 1, in which the strips 6 and 7 diverge. The capacitance between the strips at any point depends on the distance between them, which varies as they diverge.

Hence, the greater the depth to which the strips are inserted into soil 9, the less the capacitance. So, for plants requiring different moisture levels, the detector depth can be varied to alter the threshold level at which the oscillator frequency (dependent upon, inter alia, the capacitance) energises the LCD or not.

Figure 4 shows an example in which the strips 6a, 7a are generally parallel. In this case, variation of the depth of the strips in the soil causes variation of the resistance of the moist soil between the strips.

In embodiments such as those of Figures 3 and 4, changes in capacitance and/or resistance causes changes in the output (i.e. the frequency) of the oscillator, causing the LCD to be energised or not.

Figure 5 shows an embodiment, within the scope of the invention, in which an oscillator 5 generates a substantially constant output. The strips 6b and 7b are connected to the output of the oscillator and are positioned at a depth d in the soil such that when there is sufficient moisture in the soil sufficient current flows through the soil and the strips to short circuit the oscillator output, or at least reduce it to a level where the LCD is no longer energised, causing the LCD display to fail - thus indicating watering is necessary.

Claims

1. A solar powered plant moisture detector.

2. A plant moisture detector comprising at least one solar cell, means for electrically detecting moisture in soil and a display powered by the solar cell.

3. A plant moisture detector as claimed in Claim 2, comprising an oscillator and two electrically conductive strips connected to the oscillator, wherein the output of the oscillator is controlled by the capacitance or resistance between the strips to alter the display.

4. A plant moisture detector as claimed in Claim 3, wherein the strips are divergent from one another.

5. A plant moisture detector as claimed in Claim 3, wherein the strips are substantially parallel.

6. A plant moisture detector as claimed in any of Claims 2 to 5, wherein the moisture detecting means alters the output of the oscillator.

7. A plant moisture detector as claimed in any of Claims 2 to 6, wherein sensitivity of the detector to moisture is altered as the detector is pushed into the soil.

8. A plant moisture detector as claimed in any of Claims 2 to 7, wherein the display is a liquid crystal display (LCD).

9. A plant moisture detector as claimed in any of Claims 2 to 8, wherein the display bears an icon which is displayed or not dependent upon whether sufficient moisture is detected.

10. A plant moisture detector as claimed in Claim 9, wherein the icon is representative of a watering can.

11. A plant moisture detector as claimed in any preceding claim, in the form of a sheet bearing one or more solar cells, electronic components and a display.

12. A plant moisture detector as substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.