Oscillator energized liquid level indicator

Claim 1

A liquid level warning circuit for use in monitoring the level of liquid in a container, the liquid being in electrically conducting relation to one terminal of a power supply, the circuit comprising a warning device connected to the other terminal of the power supply, an oscillator connected to the power supply, the oscillator having an alternating voltage output terminal and having an inhibit terminal effective to prevent oscillation when energized with unidirectional voltage; switch means connected between the warning device and said one terminal of the power supply to selectively energize the warning device, said switch means having a control terminal capacitively coupled to the oscillator output terminal, and effective to energize the warning device in response to said alternating voltage; a probe in the container to contact the liquid at a predetermined level and electrically connected to said control terminal so that when the probe is in contact with the liquid, the switch is turned off, and when the probe is out of contact with the liquid, the switch is biased on by an alternating voltage from the oscillator to energize the warning device, first latch means responsive to the conduction state of the switch and connected to the control terminal to tend to bias the switch on once it has been turned on, and second latch means responsive to the conduction state of the switch and connected to the inhibit terminal of the oscillator to prevent oscillation when the switch has been turned on, whereby the two latch means in concert hold the switch on to continuously energize the warning device.