I am doing a hydroponics project at school.
For this I need to make a circuit for a Ph sensor, I was going crazy looking and I found only one that did not really work for me, I will add photos.
The voltages do not give me as they should give me
Where I got the schematic from is here: [Building a pH meter circuit - is it feasible?](https://electronics.stackexchange.com/questions/289548/building-a-ph-meter-circuit-is-it-feasible)
Abe Karplus did answer.

[![enter image description here](https://i.stack.imgur.com/DjdMP.png)](https://i.stack.imgur.com/DjdMP.png)
By the way, I didn't use the op amp that this man used. I used a UA741CP.

Then I used the same scheme that that man came up with to use in proteus and then make the board.
[![enter image description here](https://i.stack.imgur.com/Iw8GY.png)](https://i.stack.imgur.com/Iw8GY.png)
[![enter image description here](https://i.stack.imgur.com/3jkVX.png)](https://i.stack.imgur.com/3jkVX.png)

And this is how I got the board:
[![enter image description here](https://i.stack.imgur.com/1ah97.jpg)](https://i.stack.imgur.com/1ah97.jpg)
[![enter image description here](https://i.stack.imgur.com/kCR7h.jpg)](https://i.stack.imgur.com/kCR7h.jpg)