PH Module for Arduino controllers

terahz

terahz

1x10^12 Hz
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:
PH%20Amp%202.jpg

PH%20Amp%201.jpg


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):
<table>
<thead>
<tr>
<th class="sortable" style="width:100px" align="left">Part</th>
<th class="sortable" style="width:310px" align="left">Description</th>
<th class="sortable" style="width:180px" align="left">Digi-Key Part Number</th>
</tr></thead>
<tr>
<td style="width:100px" align="left">R1</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 150KΩ</td>
<td style="width:180px" align="left">P150KCACT-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">R2</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 10.0KΩ</td>
<td style="width:180px" align="left">P10.0KCACT-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">R3</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 4.70KΩ</td>
<td style="width:180px" align="left">P4.70KCACT-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">R4,R5,R6,R7</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 22.0KΩ</td>
<td style="width:180px" align="left">P22.0KCACT-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">R8, R9</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 100KΩ</td>
<td style="width:180px" align="left">P100KCACT-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">R10</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 2.70KΩ</td>
<td style="width:180px" align="left">P2.70KCACT-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">R11</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 15.0KΩ</td>
<td style="width:180px" align="left">P15.0KCACT-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">R12</td>
<td style="width:310px" align="left">Miniature 1/4W 1% metal-film resistor 8.20KΩ</td>
<td style="width:180px" align="left">P8.20KCACT-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">RV1</td>
<td style="width:310px" align="left">3/8" multi-turn cermet 100KΩ</td>
<td style="width:180px" align="left">T93YA-100K-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">RV2</td>
<td style="width:310px" align="left">3/8" multi-turn cermet 5KΩ</td>
<td style="width:180px" align="left">T93YA-5.0K-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">C1</td>
<td style="width:310px" align="left">multilayer ceramic capacitor 150pF</td>
<td style="width:180px" align="left">490-3689-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">C2</td>
<td style="width:310px" align="left">multilayer ceramic capacitor 3.3pF</td>
<td style="width:180px" align="left">490-3718-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">C3</td>
<td style="width:310px" align="left">multilayer ceramic capacitor 5.6pF</td>
<td style="width:180px" align="left">490-3659-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">C4, C5, C6, C7</td>
<td style="width:310px" align="left">metallized polyester film capacitor 0.1µF</td>
<td style="width:180px" align="left">BC1639-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">C8, C9</td>
<td style="width:310px" align="left">metallized polyester film capacitor 0.22µF</td>
<td style="width:180px" align="left">3015PH-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">C10, C11, C12, C14, C15</td>
<td style="width:310px" align="left">aluminum electrolytic capacitor 10µF</td>
<td style="width:180px" align="left">493-1057-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">C13, C16</td>
<td style="width:310px" align="left">metallized polyester film capacitor 0.33µF</td>
<td style="width:180px" align="left">BC1630-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">U1</td>
<td style="width:310px" align="left">LF356 JFET OP AMP</td>
<td style="width:180px" align="left">LF356N-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">U2</td>
<td style="width:310px" align="left">TL084 JFET OPAMP</td>
<td style="width:180px" align="left">497-2221-5-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">U3</td>
<td style="width:310px" align="left">ICL7660 Voltage Converter</td>
<td style="width:180px" align="left">ICL7660CPAZ-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">U4</td>
<td style="width:310px" align="left">78L05 +5V Reg</td>
<td style="width:180px" align="left">MC78L05BP-APMSCT-ND</td>
</tr>
<tr class="alt">
<td style="width:100px" align="left">U5</td>
<td style="width:310px" align="left">79L05 -5V Reg</td>
<td style="width:180px" align="left">MC79L05BP-APMSCT-ND</td>
</tr>
<tr>
<td style="width:100px" align="left">X1</td>
<td style="width:310px" align="left">BNC PCB connector</td>
<td style="width:180px" align="left">A32260-ND</td>
</tr>
</table>
 
Last edited:
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?
 
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?
 
der_wille_zur_macht said:
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?
Click to expand...
It requires a single 12V supply. I know the arduino can do 5V but you need a -5V as well...

Pinouts:
P1 -> 12V supply
P2 -> GND
P3 -> -5V out (just comes out of U5)
P4 -> VPH (goes to arduino)
der_wille_zur_macht said:
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?
Click to expand...
Yes, I tried keeping analog and digital separate. That's really the only consideration I had when I did the PCB.

der_wille_zur_macht said:
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?
Click to expand...
As far as I understand it yes, the diodes are there for voltage drop. It becomes a bit over 7V before it enters converter.

der_wille_zur_macht said:
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?
Click to expand...
For the +5V I don't see why not, I just think the schematic was designed to run on any micro that can read 0-5V.

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....
 
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?
 
der_wille_zur_macht said:
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.
Click to expand...
NP. Yeah it wasn't designed for just arduino in mind, but even with that you still can't get both +5V and -5V easily. I really looked at a lot of circuits and options and this one looked like the simplest one.
der_wille_zur_macht said:
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?
Click to expand...
I finished it on Sunday so can't really tell how accurate it is yet. Only way for me to verify how accurate it is is to test it in the calibration fluids I have (4hP ,7pH and 10pH) after a few days which I'll do. I don't have any
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.
 
Oh me me me! :lol: 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.
 
PS -

terahz said:
NP. Yeah it wasn't designed for just arduino in mind, but even with that you still can't get both +5V and -5V easily. I really looked at a lot of circuits and options and this one looked like the simplest one.
Click to expand...

Indeed, you have actually done this and I haven't, so I hope the above pontifications weren't seen as criticism. :) It just seems a shame to have half the PCB dedicated to generating the right voltage but I would defer to your judgement that this is as simple as it gets!
 
der_wille_zur_macht said:
Oh me me me! :lol: Can I trade you an LED driver board once they're finished?
Click to expand...
:lol: Sure. Let's move this part to PMs.
der_wille_zur_macht said:
Indeed, you have actually done this and I haven't, so I hope the above pontifications weren't seen as criticism. :)
Click to expand...
Not at all :)
It just seems a shame to have half the PCB dedicated to generating the right voltage but I would defer to your judgement that this is as simple as it gets!
Click to expand...
Yeah I agree. I was really hoping to find one that uses just 5V, but didn't have such luck.
 
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.
 
guido_kp said:
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?
Click to expand...
I hate etching stuff... that's why I decided to get the PCB done. I wanted to post the eagle files in the original thread but they closed it :(

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.

guido_kp said:
As far as using a 5v ph amp - the phduino circuit also works well and holds it's accuracy.
Click to expand...
yeah the phduino is a complete solution with an LCD. If I didn't have my controller already setup I would have done that most likely.

noobtothereef said:
just out of curiousity how much did they charge for the test board? I take it you sent them the eagle?
Click to expand...
The cost of the board is about $14, with shipping and handling it becomes about $25. And if you don't have any of the materials for etching a board I think it costs about the same to do your first board yourself (granted you have a lot of leftover material for future projects). They want the gerb files (already generated in the zip file in the first post) no the eagle files.
 
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
 
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:
stugray said:
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
Click to expand...
Thanks Stu, I'll take a look at and if I can squeeze it I will add it. I suppose DWZM can add this while incorporating the circuit to the reef controller. Not sure I'll be ordering anymore PCBs of this.

shackscs said:
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:
<snip>
The total was 24.65 before 6.50 in shipping.
Click to expand...
shackscs, I'll PM you about the board.

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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