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01/26/2010, 11:52 AM | #1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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PH Module for Arduino controllers
Just wanted to share this little project of mine with you. I've used a schematic from www.electro-tech-online.com by richard.c and created a PCB from it. He allowed me to make PCB and share it (Big thanks for that!) so here it is. I recreated the schematic in eagle and ordered a test board from batchpcb. Tested it yesterday and it works:
Calibration is done via the two trimmers (and can be done in software of course): dip probe in 7pH and turn RV2 until VPH reads about 1.709V clean probe with RO water dip probe in 10pH and turn RV2 until VPH reads about 2.441V I use a BRS PH probe. Here are the Eagle files (schematic, board, gerb files, gerb job file): http://joro.geodar.com/code/PH%20Amp%20eagle.zip And this is the BOM (part number, description, Digi-key part) (On the preview the table below is rendered a bout a page down, not sure why):
Last edited by terahz; 01/26/2010 at 12:01 PM. Reason: trying to fix the table |
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01/26/2010, 12:06 PM | #2 |
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Nice job! This is on my list of projects and I've compiled a bunch of schematics, but I like this one better than most I have. For one thing, the voltage regulator is right on board.
Can you explain the pinout for the header on the left side? What sort of input voltage is it looking for? I'm guessing 5v since you mentioned use with an Arduino? I know the analog signal from the probe is "weak" and I've read in other pH meter projects that the signal paths need to be treated carefully. Did you put any consideration into that when doing the layout?
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01/26/2010, 12:27 PM | #3 |
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Ok, looking at the eagle project now and I'm still a bit confused, at least on the power supply end of things.
So, the op amps need +5v and -5v. The schematic calls for +12v on the header. For the -5v side, the +12v goes into the ICL7660 converter through four diodes. The datasheet for the regulator calls for 1.5V to 10V input. Are those diodes just there to drop the voltage to within the regulator's range? For the +5v side, why not just give it +5v from the Arduino's onboard regulator? Couldn't the ICL7660 take the same +5v instead of +12v through a bunch of diodes?
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01/26/2010, 12:52 PM | #4 | ||||
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Pinouts: P1 -> 12V supply P2 -> GND P3 -> -5V out (just comes out of U5) P4 -> VPH (goes to arduino) Quote:
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As for the negative voltage, the -5V regulator requires at least -7V in. On a side note, it might be nice to put a fifth pin for +5V and use that to power the arduino.... |
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01/26/2010, 02:27 PM | #5 |
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Thanks for the answers. I suppose there's a certain amount of personal preference and/or influence from design criteria (i.e. function just with an arduino, or with any microprocessor) that goes in to some of this.
How's it working out for you? Can you verify accuracy/stability/etc against a known good meter or test kit? How long have you been using it for?
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01/26/2010, 02:58 PM | #6 | ||
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test or reliable meter. BTW I got a spare board from batchPCB (they sent me 2) if anyone is interested let me know I can mail it to you. |
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01/26/2010, 03:06 PM | #7 |
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Oh me me me! Can I trade you an LED driver board once they're finished?
Eventually I want to put a pH circuit on a shield with an RTC and some other basic reef-targeted stuff (see the thread I just started) but I'd love to have this circuit to play with in the meantime.
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01/26/2010, 03:11 PM | #8 | |
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PS -
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01/26/2010, 03:21 PM | #9 | |||
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01/26/2010, 08:54 PM | #10 |
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I etched the original circuit using the black and white board photo from the original PDF awhile ago. It's pretty stable and accurate. Could this circuit - or any ph amp - be used as an ORP amp? If not, what needs to be changed?
As far as using a 5v ph amp - the phduino circuit also works well and holds it's accuracy. |
01/26/2010, 09:22 PM | #11 |
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just out of curiousity how much did they charge for the test board? I take it you sent them the eagle?
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01/26/2010, 10:22 PM | #12 | |||
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An ORP amp should work pretty similar to a pH amp. I have not looked into it but my guess is it is a matter of changing a few resistors to get the right amplification. Quote:
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01/27/2010, 11:32 AM | #13 |
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Edit - nevermind, the parts I was thinking of exist only in my mind.
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Inconveniencing marine life since 1992 "It is my personal belief that reef aquaria should be thriving communities of biodiversity, representative of their wild counterparts, and not merely collections of pretty specimens growing on tidy clean rock shelves covered in purple coralline algae." (Eric Borneman) Last edited by der_wille_zur_macht; 01/27/2010 at 11:37 AM. |
01/27/2010, 12:24 PM | #14 |
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If you added a 1-wire AtoD (DS2450) directly to that board, you could read it over a 1-wire network.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2921 That way ANY 1-wire equipped device could read as many of them as you want. You wouldnt even need a major re-layout as the parts are so small & simple ( they dont even need power from your board ). Just two wires to solder pads for the 1-wire network and a line to the VPh & one to GND. Stu
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01/27/2010, 12:36 PM | #15 |
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How weird is this? I ordered two sets of components for this same exact design on Monday. They ship from Mouser yesterday.
Did you and DER work something out for the board? If not, I can use it. I was going to get a PCB and solder across it but the more I think about it and look at it, it would be a mess. Here is my parts list, minus the LF356 and 79l05 that mouser was out of stock on. Tell me what you think: 523-31-5431-10RFX PC R/A BLHD JCK Ni 649-DILB8P223TLF 8P IC SOCKET 855-D2814-01 14 PIN DIL IC SOCKET 512-1N4148 100V Io/200mA BULK 863-MC79L05ABDG 5V 100mA Negative 595-UA78L05CD 5.0V 100mA 700-ICL7660CPA IC VOLTAGE CONVERTER 511-TL084IN Quad Gen Purp JFET 594-2222-304-54224 220nF 5% 400volts 80-C410C151K5G5CA 50volts 150pF 10% 80-C315C569D2G C315 5.6pF 200volts 581-SR152A3R3DAA 200volts 3.3pF 72-T93XB-5K 3/8" SQ H/ADJ 5K 652-3299W-1-104LF 100Kohms Standoffs 660-MF1/4CC1503F 150K 1% 50PPM 71-CMF55100K00BHEK 1/4watt 100Kohms .1% 660-MF1/4CCT52R2202F 1/4 WATT 22K OHM 1% 71-CMF5515K000FKEK 1/4watt 15Kohms 1% 71-CMF5510K000FEEB 1/4watt 10Kohms 1% 71-CMF558K2500FHEK 1/4watt 8.25Kohms 1% 71-CCF558K25FKE36 1/4watt 8.25Kohms 1% 71-CMF554K7000FKEK 1/4watt 4.7Kohms 1% The total was 24.65 before 6.50 in shipping. Last edited by shackscs; 01/27/2010 at 12:54 PM. |
01/27/2010, 01:12 PM | #16 |
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If anyone is interested here is a link to Richard's post:
http://www.electro-tech-online.com/e...ier-micro.html |
01/27/2010, 04:05 PM | #17 | ||
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The parts look OK, if you are doing the original etched board. The resistors, however, will not fit on the PCB. |
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01/27/2010, 04:10 PM | #18 |
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I just ordered the board based on your eagle file. What was the turn around time?
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01/27/2010, 04:28 PM | #19 |
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01/27/2010, 04:35 PM | #20 |
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Wow 4-5 weeks???
Yeah, I will take your board. I sent you a pm. |
01/27/2010, 04:58 PM | #21 |
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Right on, etchings not the most fun thing I've ever done but it's nice to be able to do it. I'm using a modified phduino circuit that doesn't have the LCD portion. It's just a sensor shield. I've tried to plug my orp probe up but I never get a voltage out, is why I was asking. Tried with the trimpot all up/down but no workie.
What code are you using to derive the pH? |
01/27/2010, 06:24 PM | #22 |
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01/27/2010, 06:36 PM | #23 | |
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01/27/2010, 06:43 PM | #24 |
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When I soldered my first Protoboard for the Arduino I was turned on to doing more electronic projects, hence the phduino board project.
My board is costing 29.00 (Priority mail shipping). |
01/27/2010, 06:48 PM | #25 | |
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You can get the formula pretty easy. On this board 7pH is about 1.709V which is 0.00244V for 0.01pH; Arduino can do 1024 steps over 5V which works out to be 0.00488. So one arduino step is 0.02pH. Just multiply the value you get from the arduino readout and multiply by 0.02 and you're all set: 7pH = 1.709V = analog value 350 on the arduino * 0.02 = 7pH Replied. Just a note: I had only one extra board. DWZM claimed it first but changed his mind, shackscs asked second and he got it. I suggest if there are more people that want to make this board, just get together and do a group order, it will be much much cheaper that way. |
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