Gravity: Analog pH Sensor/Meter Kit V2 (SEN0161-V2)

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DFRobot Gravity: Analog pH meter V2 is specifically designed to measure the pH of the solution and reflect the acidity or alkalinity. It is commonly used in various…

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Can I use this on my Pi with a MCP3008 converter?

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I am looking more into it, and… it looks like I am going to have a problem, because the thing will return a voltage of 0 for PH7, and then it will go below 0 and above 0 – and the MCP* cannot read negative voltages. I would probably mess it up, trying to boost the signal to positive.

What can I do?

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Hi Tony
One way would be to use an OP amp as a level shifter. Down side is (without looking at the problem too closely) you will probably need a positive and negative power supply.
Cheers Bob

EDIT: I think it can be done with a single supply.

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Hi Tony
Just had a quick look and it looks as if the signal converter outputs a voltage 0 - 3V and seems to imply that this device takes care of the negative voltage. It is this voltage you should be measuring. Try watching some of the videos. Appears to be targeted towards Arduino or something with built in ADC and I spotted library and some code. There is also a video on using Arduino and LCD display to construct a meter so the negative voltage must be accommodated somehow. I don’t think the signal converter is able to output a negative voltage as the only supply to it is positive.

My level shifting comment above may not apply or be neccessary.

If this works with Arduino and its built in ADC I don’t see why it would not work with RPi and external ADC but I don’t know what you would do about libraries. Maybe write your own ???
Cheers Bob

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Hi Tony,

I’ve tested one of these on the bench for an RMA before, and I can say that it works fine on just a regular ADC pin on an Arduino, and I can see the product page states it can work on 3.3V, so it should work with your IO expander.

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Let us know if you have any followup questions, and cheers to @Robert93820 for being ready to dive into an op-amp based solution if it needed it, glad it doesn’t :relieved:

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Oh I am in idiot… that is EXACTLY what the extra circuit is for! (That’s the part I didn’'t feel confident building myself, as I saw a lot of “gotchas” online with loss of granularity etc.)
Perfect, I can’t wait to hook this up and start reading…

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