Hello all!
I am currently building a Ph circuit, I would like to read a Ph Probe conected via a BNC conector and outputing the analog signal via a ADS1115 chip to an ESP32 S3. Attached is my current schematic that Ive build using my own knowledge and whats available in the various data sheets. To be honest this is probably the most compext thing ive done so far and im totaly unsure if it correct, thats where is need help....

Attached is a schematic in .pdf form and here is a breakdown of what ive got and done to my understanding....

LMP7721: Used for doing the main PH reading
LMP7715: (Top left of schematic. U6) Used to supply a stable reference voltage
LMP7715: (Bottom center of schematic) Used to help filter out noise.
RKE1205: Schematic says 0505 but im using a 12v version to supply an isolated 5v power supply
IL300: Opto-copuler to isolate the output signal and eleminate an interference.
LMP7715: (Right side of circuit) used to amplify the signal before it goes to the ADS1115
ADS1115: 16bit ADC (better than the one in the ESP32)
J5: BNC conector

I have placed various Caps around the circuit to help create a nice clean signal.

What do you guys think? Total disaster or feasible? Any mistakes?

 

hi c86,
Interesting project.
The circuit diagram is very difficult to read, focus and contrast.

I would suggest a Black on White redraw.

E

 

I don't have any trouble reading it once I zoom in.

But my question is, why reinvent the wheel? You can buy a fairly inexpensive pH meter or spend increasingly more to achieve whatever level of specifications you want.

Note the lowercase p to indicate -log and the capital H for hydrogen.

 

Good question... I plan on integrating it into a project long term and want it all integrated on one PCB. If more say the Schematic needs re uploading ill take a look, I Can zoom in and see everything clearly.

 

Well OK. Have you looked at the application notes and pre-existing designs that are out there? Just search on "pH printed circuit board" or such and you'll find loads of stuff. My point is I'd personally feel a lot more comfortable using a design that's been tested, tried and true.

 

Well OK. Have you looked at the application notes and pre-existing designs that are out there? Just search on "pH printed circuit board" or such and you'll find loads of stuff. My point is I'd personally feel a lot more comfortable using a design that's been tested, tried and true.

yes true! but i Cant find anything where the full schematic is available, maybe you have something different?

I can find pre built solutions but id like to have full controll over what goes into my design and fully understand how it works.

 

yes true! but i Cant find anything where the full schematic is available, maybe you have something different?

I can find pre built solutions but id like to have full controll over what goes into my design and fully understand how it works.

There's this:
https://www.analog.com/en/resources/reference-designs/circuits-from-the-lab/CN0326.html

But I also see a ton of Arduino projects around pH.
https://www.instructables.com/ARDUINO-PH-METER/
https://bestengineeringprojects.com/arduino-ph-meter-using-ph-sensor/
https://www.sparkyswidgets.com/portfolio-item/ph-probe-interface/
https://circuitdigest.com/microcontroller-projects/arduino-ph-meter
https://www.wiringdigital.com/diy-ph-sensor/