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Robo-Tank Isolated PH Circuit
Well March 6th has arrived which has got me thinking, maybe I should forget Robo-Tank and try and invent a pause button for the calendar, that would be original and a real game changer. So unfortunately I'm not quite ready to ship today but will be ready for this coming weekend.

I officially have the circuit running on its own and for the first time I'm able to monitor my aquarium. Apparently my tank has a high source of mysterious noise as I've never been able to use my non-isolated Atlas circuit, as soon as probe touches the water the level immediately shots up past 14.0. When I was using mine with only 3.3v pin isolated the pH was showing about 4 and bouncing all over, but now fully isolated its nice and stable to the thousands.

I've already done some 2 point calibrations which works good and just received 3 different buffer solutions so I can test a 3 point calibration.
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Sorry I don't have the pH ready to ship but I'm very close. I want this to be the best it can so the last week I've been putting in a lot of work on all the formulas, especially the temperature compensation. This took a lot of research and a few headaches but I think its finished.

I was blessed to find a formula that compensates based on temperature of calibration solution and sample. Others I found was only using 0.003/C/pH but this should more more accurate overall. Here's a link if anyone is interested.

I was able to replicate their example and then using a mV per pH ratio chart I found I was able to verify it further.

Now I'm adding some last functions, going to do another bunch of different calibrations and it should be ready.
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Nice to have a proper calibration :D
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Now I'm just waiting on a new pH probe, my cheap $6 probe hasn't been doing so good lately so I had to order one before I ship these. Which probe did you end up getting? I got a Milwaukee MA913B/3 double junction.
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Slope dropped rapidly on the $6 probe?
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That has gotten worse, out of acceptable limit now, but the main problem is it's takes a long time to get a reading, I think I caused the issue by putting the probe in my tank too often without isolation. Based on Atlas if the water being measured has stray voltage it can damage the probe so isolation is required to prevent that. Mysteriously my tank has a high level of current flowing through it as the meters go off the charts when I simply touch the water with the probe. After doing this the responsiveness of the probe is horrible, if I move from buffer 4 to 7 it can take an hour to finally get a reading it will stick to, it slowly creeps up 6.432, 6.433, 6.434, etc... until it hits the max. Now I want to do a final 3 point test but having a hard time. When I started with the cheap probe I did do a 4 and 7 calibration that worked perfectly so I'm sure it'll be ok.

I ordered the probe on Amazon last Friday with 2 day shipping and to my surprise it still hasn't shipped, they've never been this slow as this is a Prime item. I hope they ship it tomorrow.
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Ever thought about fitting a groundingpole to your aquarium?
It is Just a metal bar with a wire on it which goes to a grounded outlet.
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When I discovered this I didn't have a probe to ground it and didn't want to sue wire so I left it, didn't matter as I have no need to monitor pH. Might get one now but I would love to know whats causing it lol...
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Just switch off your equipment one by one to see when it goes away, then you know what caused it.

Most likely a pump or heater
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If only it was that easy. Already did that with no luck, all I have in my tank is a heater and temp sensor and I've physically removed them in the past with no luck, that's why it's a mystery.
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Yeah But you use some form of filtration right?
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Yeah I have 2 canister filters but only plastic hoses contacts the water, I've also unplugged those in the past but it doesn't help.
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I finally have the pH circuit ready and will be shipping them this weekend, thanks to everyone who ordered.

I'm quite happy with how it turned out, it's very accurate according to the buffers and runs reliably. I can do a 3 point calibration using 6.86, 4.01 and 9.18, after calibration I get those numbers down to the 1000th's. One of the calibrations all 3 were absolutely perfect as in 6.860, etc... always within +/- .003.

Now that I've been playing a lot with pH I didn't realize how stable the readings are in 1000th's so the next update, coming in a few days, will have it displayed as 8.035 but I'm going to leave it to 100th's for rules and alerts.

I still have a bit of work to do on the library but that should be ready before the circuits arrive, this is only needed if you want to run it without Robo-Tank.

So with all the good news there is one minor issue that surprised me. About a week ago I happened to have the I2C address set to 99 and connected it to the controller and to my surprise it didn't work. Later I discovered there was an issue with the ATtiny85 wire library and the Due, only address 0-64 will work, 65-127 doesn't work. Using a Mega 2560, Uno or any other AVR all addresses work fine. I've spent nearly the last week trying everything I could to get all working but couldn't do it without writing my own Wire library which is currently above my pay grade and I have no time to figure it out.

In the big picture this is meaningless unless you have 64 devices connected to your project and they all use the lower end of the addresses. I'm not using any of these address on the controller so it's still possible to connect 64 circuits which I'll obviously never be supporting anyways.

Well you all should be getting an email in a few days confirming it was shipped.
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Good thing I didn’t update yet xD
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As quite a few ordered the circuit with an I2C buffer I made up a basic diagram showing how to connect it. There's jumpers with it that should plug directly into the controller board, +12v, GND, SCL and SDA so it should be straight forward. I added this to the download section along with the STL files to print a case for the pH circuit.

[Image: pH_with_Buffer.jpg]
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Nice, almost can’t wait to get it running
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"Almost" lol...
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Yeah have to finish the SSR “upgrade” as well
Don’t want to mant changes at once.. if something goes tits up I want to be able to pin-point it with 100% certainty
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that does look very nice going to have to print up little boxes to put them in :)
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Thanks Rott and yeah you'll have to test out your new printer, I've added the STL files to the downloads section. This is what the case looks like.

[Image: pH_in_Case.jpg]
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Current time: 10-13-2019, 11:47 PM