Audio Circuit DiagramsMetering and Instrument Circuits

Audible Level Indicator

Detect and measure the level of a liquid within a tank with level indicators. Standard technologies used to measure levels include floats, pressure or depth sensors, ultrasonic detection, and conductivity level measurement.

With this audible liquid level indicator, you may confidently pour hot drinks. Simply lay the gauge on the side of a cup, glass, or jug to check the temperature. It’s never been easier or safer to make a cup of tea or coffee.

A 600 Hz signal at a level of 2.4 Vpp, generated by the oscillator on board an LM1830 (National Semiconductor) is applied to a probe via C2. The probe is immersed in the liquid whose level is to be monitored. Because of C2, there is no direct voltage at the probe, so there are no electrolysis problems.Level Indicator

As long as the probe makes no contact with the (conductive) liquid, the signal level at the input of the detector is equal to the level of the oscillator signal. When the liquid touches the probe, the detector input is connected to the ground (or nearly so). This causes the level at pin 10 to drop. When it becomes more than 0.6 V lower than the oscillator signal, the detector switches on the internal output transistor in the rhythm of the oscillator frequency, since that is not suppressed by the detector.

The consequent signal at pin 12 is used to drive a simple output stage, T1, which drives a small loudspeaker, LS1.

The supply for the circuit is best taken from a 9 V PP3 battery. In quiescent operation, the current drain is 3 mA; when the alarm sounds, the current rises to about 80 mA.

The LM1830 fluid level detector is a device intended to signal the presence or absence of aqueous solutions. This application brief shows how to implement HIGH/LOW limit control applications utilizing this device.

Many opportunities exist for a device that can reliably control the operation of pumps or solenoid actuated valves in fluid-level control applications. Applications include sump pumps, bilge pumps, washing machines, humidifiers, plating baths, continuous replenishment photographic processors, coffee makers, municipal water and waste treatment plants, cooling towers, refrigeration equipment, and others.


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