# Arduino Diy pH probe



## Darkblade48 (Jan 4, 2008)

Another project to follow 

I should get back to coding; I've been lazy lately.


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## bigd603 (May 10, 2011)

I just got this pH stamp in the mail, excited to try it out. Which probe did you order?

You should check out the thread on the DIY aquarium controller:
http://www.plantedtank.net/forums/showthread.php?t=192436


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## Jeffww (Aug 6, 2010)

I got a standard bnc ph probe from some shipper in HK. With probes you get what you pay for but it's good enough for our hobby. 

The stamp was really easy to set up. The only thing that confused me was that the BNC breakout board had three pins so it looked like VCC was connecting to it. Took me a bit to realize it was a dead end.


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## mistergreen (Dec 9, 2006)

Laboratory grade ph kit
price $106

https://www.sparkfun.com/products/10972

Don't forget to calibrate. Setup instructions are with the link.


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## Jeffww (Aug 6, 2010)

For me it was cheaper to buy a few packets of callibration fluid than those huge bottles that go bad after 6 months anyways. Also It ended up much cheaper buying a bnc breakout, stamp, and probe and packets separately (around 70 dollars). The arduino mega 2560 and shields and what not added another 44.


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## mistergreen (Dec 9, 2006)

Jeffww said:


> For me it was cheaper to buy a few packets of callibration fluid than those huge bottles that go bad after 6 months anyways. Also It ended up much cheaper buying a bnc breakout, stamp, and probe and packets separately (around 70 dollars). The arduino mega 2560 and shields and what not added another 44.


cool, good find but the set up instructions should help you out. 

it would help if you tell us how to get the sweet deal. all through ebay?


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## Jeffww (Aug 6, 2010)

Yah the directions were all there. Atlas scientific does a really good job at explaining the set up. 

All through ebay: 

BNC break out and pH stamp were 28 + 8.00 + 6.50 shipping 
Calibration fluid was $9 shipped (bought a few packets) 
Probe was $17 shipped

I got it all via [Ebay Link Removed]


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## Jeffww (Aug 6, 2010)

Just a quick question, has anyone gotten a membrane based CO2 meter to work yet? Like using a gas membrane like a kordon bag, vegetable bag or something like that to work with a pH probe? 

I happen to have some parafilm I could get a hold of to try and make something workable with.


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## mistergreen (Dec 9, 2006)

.010" or smaller of silicone sheet works great for separating gas from water. I don't see how this helps your ph sensor. Is it a gas sensor?


Sent from my iPad using Tapatalk HD


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## Jeffww (Aug 6, 2010)

The idea is to use a gas permeable membrane to hold some 4dkh fluid and use the ph meter to measure fluctations in ph and translate to co2 concentration. Using the membrane increases response time for CO2 measurement.


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## mistergreen (Dec 9, 2006)

oh, gotcha. it costs the same to buy a CO2 sensor whose max is 36ppm 
or a bit more ($250) for a sensor whose max is 300ppm.

http://aquatictechtank.net/viewtopic.php?f=11&t=11&start=10


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## Darkblade48 (Jan 4, 2008)

Jeffww said:


> The idea is to use a gas permeable membrane to hold some 4dkh fluid and use the ph meter to measure fluctations in ph and translate to co2 concentration. Using the membrane increases response time for CO2 measurement.


I think I mentioned this in another thread somewhere, but mistergreen was working on this project 

http://www.plantedtank.net/forums/showthread.php?t=195988&highlight=


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## Jeffww (Aug 6, 2010)

Very interesting projects. 

I have one question though. It seems that my probe won't work on 3.3V VCC. On 3.3V the readings constantly fluctuate +/- .2pH on continuous measurement. On 5V it's just fine. Is there a reason this could be happening? I think it's like 1 or two things. 

1. I'm using a USB hub to connect to my laptop to power the arduino and probe so there might not be enough power to run everything at the stated voltage. 
2. My probe which was shipped from china is just inefficient. 

In the event that it's a probe problem is there a way to step up 3.3V to 5V in arduino? I'm worried I won't have enough space to run everything. I saw this thing called a logic level converter but I'm not sure that's applicable in this scenario... I don't have a multimeter with me but I guess I could try plugging it into my DC adapter to see if it works alright. 

Or alternatively is there a way to split the 5V into multiple connection points so I can run my LCD and my probe. 

edit: 

I've read that I can split it through a parallel circuit with any number of devices whose total draw is less than 1A so that I don't fry my components. Does that sound right?


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## mistergreen (Dec 9, 2006)

you can use resistors to limit voltage and current. Ohm's law. Knock down to what you need for the lcd and leave it at 5V for the pH sensor.

Get yourself a breadboard and test things out first before you start soldering. There's a process that makes life easier.


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## Darkblade48 (Jan 4, 2008)

Jeffww said:


> Or alternatively is there a way to split the 5V into multiple connection points so I can run my LCD and my probe.
> 
> edit:
> 
> I've read that I can split it through a parallel circuit with any number of devices whose total draw is less than 1A so that I don't fry my components. Does that sound right?


As mentioned, you can split your 5V line along a breadboard/protoboard and then use some resistors to power both your LCD and pH probe.

Alternatively, you could always just write one pin high so that it's at 5V (less efficient).

As a side note, the Arduino can only provide 500 mA maximum. There are other restrictions on certain pins (i.e. total of X to Y can only be 200 mA, etc). The Arduino website has the specifications for these current draw limitations.


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## Jeffww (Aug 6, 2010)

Really? I thought it was a 500ma max if it draws from a computer USB and 900ma if it took from a 9V adapter. Or rather, it would draw since there is no regulator as much as it could until something broke with 900ma being the general safety limit either in built to some arduino or just as a precaution.

edit: also why would I need resistors to bring down the current for the LCD? Why can't I directly wire them in parallel.


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## Darkblade48 (Jan 4, 2008)

It is definitely 500 mA maximum if drawn from USB. I am not sure what the maximum total current draw is when using an AC to DC adapter. 

Each pin can supply a maximum of 40-50 mA, depending on which board revision you have.

To be honest, if you find yourself needing to draw more than 500 mA, you should be using a separate power supply anyway.


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## Jeffww (Aug 6, 2010)

That being said, it shouldn't really take that much current to run just a probe (a couple of ma at most) and an LCD though....So dividing the 5V pin seems pretty safe.


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## Jeffww (Aug 6, 2010)

So I've got the pH displaying on the LCD at this point, working on button controls. However, I'm encountering some really weird problems. When I run the set up on its own directly from the outlet power it gets crazy pH fluctations. It's only stable when it's attached to my computer. I'm starting to think that my adapter is messed up.


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## mistergreen (Dec 9, 2006)

too much or not enough current maybe. Check on how much voltage & current for optimal function.


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## Jeffww (Aug 6, 2010)

Will do. Although I wonder why it would work fine connected to the pc but not to the wall?


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