Using pH and EC probes from abandoned project

Hi guys,
I got a pH and EC probes from a friend, from a previous project. I only got the probes, with a wire that ends with a screw-in connector (sma).

I searched (as I am in China, on Taobao), and bought a board that seems to be compatible with this probe and has serial interface:

https://item.taobao.com/item.htm?spm=a1z09.2.0.0.44ae2e8dBvRBm6&id=564037326797

I was planning to use the onboard UART to read from this board. However, its voltage is 5V, while the UART on Raspberry is 3.3V. No-go.

There is also an analog output on that board, which outputs between 0-3.3V depending on the measured pH. I suppose I should be able to use ads1115 to read the voltage, and calibrate this in Mycodo?

Would you recommend me doing this, or better getting a USB 5V UART adapter and writing a custom input for this sensor (it has AT commands for calibration, read a measurement, etc.)?

Another part of the question is for the EC probe. It has the same connector. If I get another board of same type, and use the analog voltage output, should I be able to calibrate it using my manual EC probe? (measuring the same liquid with both, and entering the manual meter value into calibration process in mycodo)?

Would this kind of setup be reasonably reliable?

Cheers, and thanks for your awesome videos Kyle, kickstarted my interest in hydroponics, I built a compact vertical system in the Xinchejian hackerspace in Shanghai. Can’t wait to have the automation done (now I do everything by hand…).

Lukas

Hi Lukas.

I would recommend using a level shifter. Inexpensive and then you can use all the features of the board (commands) rather than just being able to use an output voltage.

I’m not sure. The board connected to the probe typically stores the calibration data. Mycodo only has a few modules that perform and store calibration data within the Mycodo database, and these are only for modules that use an analog-to-digital converter and receive an output voltage from the board. The others merely send the calibration command to the board and the board performs/stores the calibration.

Thanks for the reply!

I think I will go for a USB UART, then - seems to me it should be more reliable than using a level shifter, plus I might need 2xUART, and the raspi gpio only has one available, afaik.

And with the EC meter, I might not be able to use it, then. I was not able to find any board that would offer this functionality.

Will update the topic after I get some progress.

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I would say pH probes are fairly universal and easy to drive/read, so your approach with the Taobao part is great.

For the EC probe, perhaps you can see if one of the dfrobot parts (e.g. this or this) will work for you. You’ll have to use their EC drive board to drive the probe, then read the analog voltage via an ADC (e.g. ADS1115, supported in Mycodo). Last I checked, they don’t sell the drive board separately from the kit if you go through the dfrobot.com website. You might have to talk to them directly, or maybe you could find their Taobao/JD page. They’re based in China so you’ll probably get better pricing anyway!

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