Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1974-12-13
1976-09-07
Corbin, John K.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
324 65P, 324 96, G01R 2720
Patent
active
039796671
ABSTRACT:
A domestic soil-moisture indicator of the kind including a probe comprising a pair of electrodes with spaced ends for insertion in the soil whereby the resistance of the conductive path established between them by the soil to be tested varies in resistance with the moisture of the soil. The improvement comprises a control circuit responsive to the value of the variable resistance and including a pair of light-emitting devices, connected in such a way that the total power between them is substantially constant and, at one end of the scale of value of the variable resistance, one device is fully on and the other is off, while at the other end of the scale the one device is off and the other is fully on, the brightness of the two devices varying between these extremes for intermediate values. The light-emitting devices are preferably light-emitting diodes each of which is connected in series with one of a complementary pair of emitter-following transistors connected to the division point of a potential divider consisting of the variable soil resistance and a fixed resistance connected in series with one another across the source of supply.
REFERENCES:
patent: 3452347 (1969-06-01), Stimson
patent: 3688309 (1972-08-01), Volberg
patent: 3882383 (1975-05-01), Matlin
Corbin John K.
Diplex Limited
Punter Wm. H.
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