EC and pH Sensor Interface Review Request

[mindoo]

Hi everyone,

Hopefully this is the right place to post this, but let me know if another place would be more suited.

I am currently working on an automated hydroponics system and have been in the process of designing a PCB to serve as mainboard for the device. This entails interfacing our 2 most important sensors EC and pH, a couple various other sensors and pump signal lines with an ESP32-S3-DevKitC-1 (https://docs.espressif.com/projects/esp-idf/en/stable/esp32s3/hw-reference/esp32s3/user-guide-devkitc-1.html) that will in the future be replaced with it's own onboard ESP32.

The pump interfacing is done by another PCB which will connect to the mainboard using RJ45 cables. This mainboard design accounts for 2 RJ45 ports that will connect up to 8 pumps total.

I am especially interested in getting feedback on the EC sensing circuit implementation as well as the pH sensing implementation as those are the main features I am trying to validate. Both of these implementations are based on demonstration boards from analog instruments ([CN0411](https://www.analog.com/en/resources/reference-designs/circuits-from-the-lab/cn0411.html) for the ec, and [CN0326][https://www.analog.com/en/resources/reference-designs/circuits-from-the-lab/cn0326.html)]. As I'm relatively new to electrical engineering, it took me a while to wrap my head around the implementations of these sensor interfaces which is why I have not strayed away too much from the original designs. I'm sure there's many optimisations to be made around IC choice, cost reduction and so forth, however I've made not attempt at those, and am solely focused on trying to get everything up and running while testing my understanding of the circuit. With this review I'm especially hoping to catch issues that would prevent the circuit from functioning normally.

In order to help any potential reviewers, I have written up detailed implementation notes that I'll link with the review material. These include a very extensive list of all my uncertainties surrounding this circuit, this really isn't meant to be read much, though I thought it wouldn't hurt to leave it in.

Links (Files are also attached to this post) :
- Implementation Notes PDF: https://drive.google.com/file/d/1tYtIdJFU45zj1r5AZHM39aGDggFg5p3v/view?usp=sharing
- Schematic PDF: https://drive.google.com/file/d/1tsIcaM-5KdnTbJHeIFHExXxQLHZJVNg9/view?usp=sharing
- Schematic Kicad Files: https://drive.google.com/file/d/1LtTQpykrx45qPEkoOcKh6Cvc3GtTJSTG/view?usp=sharing
- Analog Devices CN0411 - EC Interface Evaluation Board: https://www.analog.com/en/resources/reference-designs/circuits-from-the-lab/cn0411.html
   - Driver Code Repository: https://github.com/analogdevicesinc/arduino/tree/master/Arduino%20Uno%20R3/examples/CN0411_example
   - BOM Google Sheets: https://docs.google.com/spreadsheets/d/1yz2csW18CT-3OzN2g8EsE3BTaIYoo1P1Ldm9dg3V3q0/edit?usp=sharing
- Analog Devices CN0326 - pH Interface Evaluation Board: https://www.analog.com/en/resources/reference-designs/circuits-from-the-lab/cn0326.html#rd-description
   - Driver Code Repository (not C): https://github.com/analogdevicesinc/EVAL-ADICUP360/tree/main/projects/ADuCM360_demo_cn0326
   - BOM Google Sheets: https://docs.google.com/spreadsheets/d/1pJwaqCliwP82ywKciFpqMz8PMwcJ7EX3LoeK3Fzv3zE/edit?usp=sharing

I really appreciate any time anyone spends looking at this, and every single ounce of feedback is greatly appreciated ! Thanks guys

[xvr]

One note so far - you don't needed LDO for 3.3V. ESP32 DevKit includes one.

[mindoo]

Yeah I included that still as the use of the devkit is really just for the first version.