How can I amplify mV to V for a pH regulator proyect?

As a pH regulator, my proyect should measure first the pH of the solution with a pH probe. The analog measurement is given to me as mV (pH 0 = 400mV, pH 7 = 0mV) how can I amplify the signal? Which of all the op-amp should I use?

I so new at this Arduino tech stuff, I'm a sophomore in college, can someone help me?

You need a precision instrumentation opamp, I don't have types at hand. Very high input impedance, with input bias in the low pA or preferably fA levels.
You also need a voltage bias to offset the readings or you can't read the other half of the pH values.
Finally you have to worry about ground loops, a major issue with those things.

IMO you should try to find professional modules for that sensor type, with a digital interface. Reliable circuits are not easy to DIY.

At the very least you should use a proper PCB, not perfboard or so. That should go a long way in getting it to work.

wvmarle:
You need a precision instrumentation opamp, I don't have types at hand. Very high input impedance, with input bias in the low pA or preferably fA levels.
You also need a voltage bias to offset the readings or you can't read the other half of the pH values.
Finally you have to worry about ground loops, a major issue with those things.

Would you recomend an opamp? Which one?

I got some answers from a friend and he said I should use a Wheatstone Bridge and instead of using a galvanometer just connect the probe. Does that make sense? Should I do that? My friend is an electric engineering student.

DrDiettrich:
IMO you should try to find professional modules for that sensor type, with a digital interface. Reliable circuits are not easy to DIY.

I have and they are roughly 40 bucks on the market. If I order it online is somewhat less pricey but with international shipping the price goes a lot up.

Sadly, as I have another 3 proyects to deliver before end-of-term I can't spend that kind of money.

wvmarle:
At the very least you should use a proper PCB, not perfboard or so. That should go a long way in getting it to work.

What does using a PCB board has to do with this? Im using it because I was asked to. Does it change something in the performance of the ph probe? I didn't think it would.

If you - obviously - don't know about building reliable electronic circuits, you should ask your friend or some other sufficiently skilled person for assistance.

I'm currently testing the LMP2232 OpAmp (input bias 20 fA), in combination with a TL431BC voltage reference for the offset (2.495V brought down with voltage divider to about 450 mV) to get a 0-1V output signal for pH=0-14. Using an ESP8266.

Stability is OK so far (running a test with a pH=7 buffer). Using my hand as shield over the OpAmp improves stability - that's how sensitive this kind of circuits is, and that's while I even used copper pours on the PCB connected to the offset voltage (and the shield of the pH sensor wire) to shield the trace coming out of the pH probe.

Found quite a bit of noise on the output (almost 20 mV peak/peak on the scope), the 220 pF cap I had there already was not enough. Added 47 nF to get rid of that noise. Not sure what causes it, getting rid of noise at the source is always better. A primary suspect is the two carbon film resistors that ended up in that part of the circuit, I probably should have used the metal film ones. SMD parts should also allow for improvement over the through-hole that I used.

Possible improvement of the circuit would be to use a VSSOP package so I can place it even close to the BNC connector. It's now connected through a trace of about 5 mm long.

That are some of the considerations that go into building a pH circuit.

wvmarle:
I’m currently testing the LMP2232 OpAmp (input bias 20 fA), in combination with a TL431BC voltage reference for the offset (2.495V brought down with voltage divider to about 450 mV) to get a 0-1V output signal for pH=0-14. Using an ESP8266.

Stability is OK so far (running a test with a pH=7 buffer). Using my hand as shield over the OpAmp improves stability - that’s how sensitive this kind of circuits is, and that’s while I even used copper pours on the PCB connected to the offset voltage (and the shield of the pH sensor wire) to shield the trace coming out of the pH probe.

Found quite a bit of noise on the output (almost 20 mV peak/peak on the scope), the 220 pF cap I had there already was not enough. Added 47 nF to get rid of that noise. Not sure what causes it, getting rid of noise at the source is always better. A primary suspect is the two carbon film resistors that ended up in that part of the circuit, I probably should have used the metal film ones. SMD parts should also allow for improvement over the through-hole that I used.

Possible improvement of the circuit would be to use a VSSOP package so I can place it even close to the BNC connector. It’s now connected through a trace of about 5 mm long.

That are some of the considerations that go into building a pH circuit.

By far one of the best responses I’ve ever gotten on the whole community, I think I can work with this with some help and instruction. Now I understand the PCB involvement in this.

I imagined this proyect would require a lot, I hope it all goes well. If you have more advice you can give me, I’ll be very thankful

Thank you for the reply.

Read up on ground loops. They're the nemesis of pH probes, and there's no easy way of galvanic isolation of a pH probe.

liaannee:
As a pH regulator, my proyect should measure first the pH of the solution with a pH probe. The analog measurement is given to me as mV (pH 0 = 400mV, pH 7 = 0mV) how can I amplify the signal? Which of all the op-amp should I use?

I so new at this Arduino tech stuff, I'm a sophomore in college, can someone help me?

Use an INA (Instrumentation Amplifier), such as the AD620, keep an eye in proper PCB design and avoid any ground loops when possible.

Will be wise to choose an ADC with at least 12 bits.

Good luck!

yv1hx:
Use an INA (Instrumentation Amplifier), such as the AD620,

Did you actually read that data sheet? The input bias current is HUGE! 1 nA is totally unsuitable for pH probes. The OpAmp I suggested is doing 5 orders of magnitude better on that.

A 10-bit ADC perfectly adequate for practical purposes and normal pH probes. You won't get much better than 0.1 pH point in the real world, that's 140 steps over the 0-14 part. A 10-bit ADC offers 1024 steps. 12-bits doesn't make a difference, it just adds noise.