Page 1 of 1

Powering the Analog Turbidity Sensor from 3.3VDC

Unread postPosted:Fri Jul 19, 2019 9:44 am
by Lucas.stromberg
Hi! I'm using a Particle Electron as a microcontroller with the turbidity sensor. However that board only has 3.3V pins, and in my use case I can't use the Vin pin since I'm not charging by USB. I figured this wasn't a big problem since the sensor will work with 3.3V as well, however since my domain (0-3.3) isn't the same as the one in the example at https://wiki.dfrobot.com/Turbidity_sensor_SKU__SEN0189 (0-4.5) I can't use the equation that converts voltage to NTU.

At first you'd think that you could just multiply all readings with 3.3/5, however I learned that the relation between 3.3V and 5V readings is not linear. E.g. if I take a measurement in clear water with 3.3V and 5V and then do the same in dirtier water, the differences between the voltage values don't follow a linear path. Note that I learned this by taking measurements with an Arduino that can supply both 3.3V and 5V. However, I won't in my real project be able to use the Arduino.

The only solution I can think of is to take multiple samples with 3.3V, and then with 5V, and then create a function to map readings done with 3.3V to a "theoretical" reading done with 5V. However I'm hoping that there would be a better (more correct) way to do this. For example is there a similar equation to the one in the link above, but for when you use 3.3V to power the sensor instead of 5V?

Thanks!

Re: Powering the Analog Turbidity Sensor from 3.3VDC

Unread postPosted:Mon Jul 22, 2019 1:53 am
by nana.wang
Hi Lucas,
Thanks for your support.
We will check it and feed you back as soon as possible.

Re: Powering the Analog Turbidity Sensor from 3.3VDC

Unread postPosted:Mon Aug 05, 2019 9:36 am
by xuegangxiao117
Hi,
Actually, I'm not sure if it's possible to use this 5V module on a 3.3V platform. It is able to show the data, but it doesn't mean the output is correct. (I have inquired the PM and I will update this info as soon as I get responded.)
There is no equation for this. But I think you can test multiple times at different turbidity and draw your own turbidity and voltage characteristics.

Re: Powering the Analog Turbidity Sensor from 3.3VDC

Unread postPosted:Wed Aug 07, 2019 1:33 am
by nana.wang
Well, from the test of NTU<0.5, the output voltage is 4.1 ± 0.3V, and you can check the equation via https://raw.githubusercontent.com/DFRob ... iagram.jpg

Re: Powering the Analog Turbidity Sensor from 3.3VDC

Unread postPosted:Thu Apr 22, 2021 8:34 pm
by zachary_fields
To use the SEN0189 on a 3V3 microcontroller, you need to use the 3V3 equation, instead of the 5V equation.

3V3 quadratic equation:
y = -2572.2x² + 8700.5x - 4352.9

The steps to derive this equation are on the Arduino Forum.
https://forum.arduino.cc/t/getting-ntu- ... /658067/14