Abstract: A bi-directional communication assembly is provided with commonly available optoelectronic components in a compact package. Diplex functionality is achieved by orienting the receiving detector at an angle with respect to the transmitting beam. An interference coating inside the detector, on the detector surface, or on a surface in intimate contact with the detector, reflects the transmitted beam while simultaneously allowing the receiving beam to pass through the coating to the light absorbing region. The combined function of the receiving detector, providing advantages of a common beam path and close proximity of the components, enable a compact package that can be placed within the space usually occupied by the transmitter light source alone.

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.