Abstract: A ringer circuit for a telephone is disclosed which is equipped with a transformer, having its primary winding connected to the telephone line through hook-switches. The secondary winding of the transformer is connected to a rectifying circuit so that it may convert the high voltage and low current of the ringer signal received into a secondary ringer signal having high current and low voltage. This secondary ringer signal is rectified and fed to an oscillator which drives a sound generator to provide a call signal.

Abstract: The power supply is powered preferably from a conventional AC input line by way of an AC adapter and preferably provides DC voltage levels of -5 volts and +5 and +12 volts. The -5 volt level uses a single zener diode for regulation while the other two logic levels use voltage regulators each having pass transistor means associated therewith. The circuitry also includes current limiting circuitry and filter means.

Abstract: A soil moisture sensing device employs a pair of indicator lamps to indicate whether the soil is too dry, too wet, or has the correct amount of moisture. The device need employ only one transistor or one Darlington transistor pair to control both indicators. Consequently, the device is more economical to manufacture than "prior art" soil moisture sensing devices that must use two or more transistors. In the invention, too dry soil is indicated by non-conduction of the transistor with neither indicator illuminated, adequately moist soil is indicated by partial conduction with one indicator illuminated, and too wet soil is indicated by full conduction with both indicators illuminated.

Abstract: A frequency band pass circuit having an amplifier that has an amplifying state and may be selectively deenergized to a non-amplifying state. A reverse bias is placed on the amplifier when in the deenergized state to provide substantially the same band pass characteristics of the circuit in the non-amplifying state as in the amplifying state and to reduce the insertion loss impedance through the amplifier in the non-amplifying state.

Abstract: For use with radio receivers adapted to receive both frequency and amplitude modulated signals, a frequency modulated signal preamplifier adapted to be serially connected between the antenna input lead and antenna connector of such a radio, the pre-amplifier including means for separating the amplitude modulated and frequency modulated signals, amplifying the frequency modulated signals, and recombining the signals for input at the antenna input terminal of the receiver.