Liquid Flow meter using infrared sensors

Thread Starter


Joined May 19, 2014
Hi, in my final graduate project i'm thinking to project a liquid flow meter using infrared sensor (phototransistor) and a microcontroller.

The main idea its to do 2 horizontal lines of tranceivers and receivers with a know vertical distance between then.

The infrared receiver it will generate a Vout that depends of the opacity of the liquid.

My idea is to measure in the first line, the Vout voltage with the A/D converter of the microcontroller and the time that the voltage was measured.
The second line of the receivers it will do the same measures (Vout and the time).
With the measures done, the time of the SAME Vout measures it will be compared, and with this data i can measure the speed of the liquid.

An example:

The firts line receivers generate 3.2V at Vout that was readed at A/D converter at the time 300ms.

The second line of receivers reads 3.2V at the time 320ms.

The diference between the time of the measures is:
320 - 300 = 20ms.

If the distante between the line of the receivers is 3cm, i can measure the speed:
speed = 3cm/20ms

The question is: It's possible to do this or the complexity it will be huge?

Any ideas how to start?

Sorry for the bad english.



Joined Feb 19, 2010
The only way I see this working is to use some coloring agent when you need the speed measurement. Meaning, the fluid normally has opacity X, when you want to measure fluid velocity you introduce a coloring agent, the fluid opacity changes Y, the coloring agent passes through first sensor and time is recorded, the coloring agent passes through the second sensor and time is recorded, the fluid returns to its original opacity X, your uC does the math and displays the result.

The change in opacity is the key to taking measurement.

I think food coloring should be safe for most nonindustrial applications.

Thread Starter


Joined May 19, 2014
Thanks for the reply shteii01.

yes, the change of the opacity of the liquid it will be very important.

I was thinking to test it with process that the opacity of the liquid changes during the time.
I think there is a lot of industrial applications that the liquid changes during the process.
Like cow milking, coffee machine and others.


Joined Feb 11, 2008
Or you could google for "electronic liquid flow rate sensor" and find hundreds of ready made flow rate sensors that are reliable AND already calibrated. :)

Thread Starter


Joined May 19, 2014
Hi THE_RB , thanks for the reply.

Yes it has manny devices ready made, but the objective is to build one for my final graduate project in Computer Engineer.
I'm looking for suggestions and hints to where start.