This circuit basically is a fluid level alarm indicator intended for alerting visually impaired individuals regarding the liquid level in a container such as cup, glass or bowl.
The unit can be simply hooked up across the rim of any container with the probes such that it detects the full level liquid in it while the container is being filled, and triggers ON the audible indication.
The container could be a cup, glass, bowl, bottle etc.
The circuit will detect the filling of the cup with any liquid that conducts electricity, such as beer, tap water, tea, milk.
Circuit Diagram
This also means that the circuit will not be able to detect distilled or deionised water.
Circuit Description
The circuit is extremely straightforwad to build and understand.
The entire circuit is built around 4 NAND gates using IC 4011.
N1 and N2 are configured as logic inverter/buffer.
With no liquid around the probes the input of N1 is held at a low logic due to the ground 1M resistor. As soon as the probes come in contact with a liquid in the cup or glass the N1 input is instantly pulled high. This causes N1 output to go low, which turns N2 output HIGH, enabling the operation of astable multivibrator N3/N4.
The astable switches T1 and T2 ON/OFF giving rise to an audible warning tone from the speaker.
The frequency of the astable built using N3/N4 gates can be chnaged by tweaking the values of the resistors 820 k, 390 k or the capacitor 1.2 nF. This will in turn help to adjust the tone on the speaker. It can adjusted from a sharp ear piercing tone to a milder buzzing sound, as per the user preference.
Parts List
- 1M = 1
- 390k = 1
- 820k = 1
- 27 k= 1
- 100 ohm = 1
- Capacitor 1.2 nF Disc ceramic
- Transistor BC108 or BC547 = 1
- Transistor 2N2222 = 1
- IC 4011 = 1
- Battery 9 V PP3 = 1
- Small 8 ohm speaker 0.2 watts = 1
Using IC 555
A tiny, cup full indicator circuit could be also created using the IC 555, as shown in the above diagram.
The IC 555 is rigged as an astable multivibrator. As long as the probes are not touching the liquid inside the cup, the astable generates a low frequency 15 Hz clicking sound on the speaker.
When the cup is full, and the probes come in contact with the liquid, the frequency of the astable suddenly increases to 500 Hz sharp tone, which alerts the user regarding the cup full condition.
The speaker could be replaced with the piezo buzzer transducer also, to make the design very compact.
U Harsha Vardhan says
Hello! If there is a chance to add led for indication purpose what would be the circuit or the changes to be done?
Swagatam says
Hi, You can connect a LED across the N2 output and the ground line, via a 1K resistor
U Harsha Vardhan says
Yeah thanks! But we haven’t used 1K resistor in the circuit using IC4011
Swagatam says
1K should be put in series with the LED
Harsha Vardhan says
Yeah Thank you!I look forward for your reply.
Can we connect both buzzer and led in the same circuit using IC 4011?
Swagatam says
yes you can put an LED in parallel to the speaker, but attach a 470 ohm resistor in series with the LED
U Harsha Vardhan says
Hii!
May I know the capacitor values for above circuit using 555timer?
Swagatam says
C1 = 0.1uF/50V
C2 = 22uF/25V
C3 = 0.01uF/50V
Gina says
Hi, I am a college student in Korea.
I want you to give me some help about my project.
I am designing circuits for people who is visually impaired. So i am making a cup that can indicate them with sound to avoid water flow.
I want to add buttons so that they can drink the water they want.
For example,
Button 1 pushed—-> when 0.2L water poured, the buzzer is ringing
Button 2 pused—-> when 0.4L water poured, the buzzer is ringing ,,,
I referred to your page “simple water level indicator“ but it is hard to put several buzzers and buttons and remove leds.
I look forward your reply thank you.
Swagatam says
Hi, How should the buttons work on the cup? The buttons are supposed to be on the water tank I guess!
Gina says
I want to control switch(button) depending on water level.
I want to know how to connect switches(buttons) with water level control circuit
Swagatam says
In that case we may have to use a timer circuit and a solenoid based water controller. The timer circuit will keep the solenoid switched ON for the specified amount of time which will decide how much water to be dispensed and cut off…
Željko Kiš says
Maybe take the relay instead speaker,instead 2N2222 some other transistor and circuit will be water tank controller.