Soil moisture indicator device

• US 4,020,417 A
• Filed: 11/26/1975
• Issued: 04/26/1977
• Est. Priority Date: 11/26/1975
• Status: Expired due to Term

• Current Assignee: Turf Service Laboratories Incorporated
• Original Assignee: Turf Service Laboratories Incorporated
• Inventors: Wheeler, Carlos E., Brehob, Alfred W.
• Primary Examiner(s): Swisher, S. Clement
• Assistant Examiner(s): Corr, Denis E.
• Application Number:
  US05/635,389
• Time in Patent Office: 517 Days
• Field of Search: 73/73, 324/65 P, 324/65 R, 340/235, 200/61.04, 200/61.05
• US Class Current: 324/694
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: G01N 27/048 for determining moisture content of the material
• CPC Class Codes: G01N 33/246 for water content
• CPC Class Codes: G01R 27/02 Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant by measuring phase angle only G01R25/00

Abstract

A soil moisture indicator device for plants comprises an electrical circuit which includes an unbalanced resistive bridge having the common junctions of the resistors on its opposite sides connected to control the switching of a pair of indicator lights. Current drawn through the resistance of the soil as sensed by a probe is used to adjust the output voltages on the sides of the unbalanced resistive bridge to switch on one of the indicator lights if the soil has at least an adequate moisture content and to switch on the other of the indicator lights if the soil has an excessive moisture content.

Claims

1. An indicating device for testing the moisture content of soil about the roots of a plant comprising:

a power supply,

a first indicator circuit connected across said power supply and including a first semiconductor switching means in series with a first indicator light,

a second indicator circuit connected across said power supply and including a second semiconductor switching means in series with a second indicator light,

control circuit means connected across said power supply with its current path completed through the soil to be tested, said control circuit means comprising an unbalanced resistive bridge having junctions on the opposite sides thereof respectively providing output voltages for controlling said first and second semiconductor switching means,

whereby said control circuit means adjusts the output voltages on said junctions in response to the resistivity of the soil to cause one of the semiconductor switching means to conduct to illuminate its associated indicator light if the moisture content of the soil is at least adequate and to cause the other said semiconductor switching means to conduct to illuminate its associated indicator light if the moisture content of the soil is excessive.

2. The invention is accordance with claim 1 wherein said first and second indicator lights are light emitting diodes.

3. An indicating device for testing the moisture content of soil about the roots of a plant comprising:

a power supply,

a first indicator circuit connected across said power supply and including a first transistor having a first indicator light connected in the collector-emitter path thereof,

a second indicator circuit connected across said power supply and including a second transistor having a second indicator light connected in the collector-emitter path thereof, and

control circuit means connected across said power supply with its current path completed through the soil to be tested, said control circuit means comprising an unbalanced resistive bridge having the common junctions of the pairs of resistors on opposite sides thereof connected to the bases of the respective transistors,

said control circuit means being operative to provide a first bias voltage on the base of said first transistor to cause it to conduct to illuminate said first indicator light when the resistance of said soil is indicative of at least an adequate moisture content therein and being operative to provide a second bias voltage on the base of said second transistor to cause it to conduct to illuminate said second indicator light when the resistance of said soil is indicative of an excessive moisture content therein.

4. A device for indicating the moisture content of the soil about the roots of a plant comprising:

a probe including a conductive tubular member and a conductive end member interconnected by an insulating spacer,

a hollow handle mounted on the upper end of said probe,

said hollow handle including therein a battery and a printed circuit card, and

said hollow handle having a pair of light emitting diodes positioned in a pair of openings in the wall thereof,

said circuit card having circuit means thereon connected to said battery, said pair of light emitting diodes, said tubular member and said end member,

said circuit means comprising a first indicator circuit including a first transistor having one of said light emitting diodes connected in the collector-emitter path thereof, a second indicator circuit including a second transistor having the other of said light emitting diodes connected in the collector-emitter path thereof, and an unbalanced resistive bridge connecting to said end member and having its circuit through the tubular member to the power supply completed through the soil in which the probe is inserted, the common junctions of adjacent resistors on the opposite sides of said bridge connected to provide voltages for biasing the bases of the respective transistors,

whereby when said probe is inserted into the soil said circuit means responds to the resistivity of the soil to cause one of said light emitting diodes to become illuminated if the moisture content of the soil is at least adequate and to cause the other of said light emitting diodes to become illuminated if the moisture content of the soil is excessive.

5. The invention is accordance with claim 4 wherein said handle includes a battery access opening having a readily removable cover panel therefor.

6. The invention in accordance with claim 4 wherein said printed circuit card is mounted to lie in an axial plane within said hollow handle.

7. The invention in accordance with claim 4 wherein said light emitting diodes are positioned in a pair of openings provided in a recessed portion of the wall of the handle.