Help with Ph sensor pin abbreviations

Help me, i tried the program on page 1, i have done calibration, by short the BNC pin, and getting 2.6 v

  1. after that I tried with a solution of 6.89 and can not produce 6.89 but lebh of it smpai value 7.3
  2. then when trying 4.01, the resulting value is more than that 4.8

What makes me confused when the BNC probe on boar I hold, the results obtained even precision, when released value will be chaotic, what happens from my board?

I connect directly
Pin VCC to 5volt arduino mega
Pin G to Ground arduino mega
Pin P0 to A0 arduino mega

please help me, thanks

Apparently you missed the part of calibration where you adjust the slope and offset in your software to match the sensor's response.

Hi all,

I think this thread is really great because it is the sole source of information on this pH sensor board. Thank you so much for contributing to it and providing so many useful details.

I'm posting here because I'm encountering an issue with the first step of the calibration. The pins are connected as follow:

  • V+ to 5V
  • G to the ground of the my power source and the COM port of my multimeter
  • Po to the V port of my multimeter
  • Do and To to nothing
    In addition, I used a wire to shorten the BNC connector.

When I adjust the potentiometer by the BNC connector, nothing happens on my multimeter which continuously reads 1.88V. If I remove the wire used to shorten the BNC connector, the voltage remains the same.

Does that mean that my board is defective/broken?

Coos:
Hi All, I've got the same Ph module, and found this thread very useful!
Special thanks to LeCyb and normen!

I've got one problem though:
When I measure my aquariumwater in the tank the ph goes all over the place, from ph4 to ph8...
When I measure the same water in a cup, I'm getting a steady reading.

So something is interfering I guess...
Anyone got an idea of how to approach and solve this problem?

Same problem here.. As soon as I put it in the voltage goes crazy with random values, but I can take a cup of the same water and it is fine. like porlock I assumed this must be some piece of equipment causing it so I unplugged everything and it is still occurring. I also notice as soon as the probe goes in the aquarium the red limit LED on the board comes on and stays on.

Did you ever solve this issue? I wonder if my issue can be solved by a grounding probe if it still occurs when no equipment is connected?

Sounds like you're having ground loop issues. Can be very hard to solve.

wvmarle:
Sounds like you're having ground loop issues. Can be very hard to solve.

Yes I think you are correct. I did some testing and powered my board from a battery and while the voltage swings were higher than I liked they were no longer wildly fluctuating.

From my research it looks like I can either try to isolate the ph probe or isolate the entire circuit. I found some dc/dc isolated converters like this that look like they should work. This will mean another pcb revision which is annoying, unless anyone knows of a 5v wall adapter that has an isolated converter in it?

For your wall adapter: any with a transformer in it should give you full isolation.

Mind that ground loops are generally within your circuit, so through other sensors in the water (such as EC probes or temperature probes).

Hey guys,
Has anyone encountered an issue where the pH value keeps climbing on its own (given like a 2 min. span) and won't keep stable?
I have my probe sitting in factory calibrated 7.0 pH solution, so I know that it's not a solution issue.
Any help/advice would be great!

Here's my sketch as it is:

/* 7.0 Solution
 *  Measure: 512
 *  Voltage: 2.5
 *  PH: 7.0
 *  
 *  4.1 Solution
 *  Measure: 619
 *  Voltage: 3.02
 *  PH: 4.01
 */

int Po_Pin = A0; //Pin Po on the pH sensor board connects to Arduino pin# A0.
int Do_Pin = 2; //Pin Do on the pH sensor board connects to Arduino pin# 2.

void setup() 
{
  Serial.begin(9600);
}

void loop() 
{
  int measure = analogRead(Po_Pin);
  Serial.print("Measure: ");
  Serial.print(measure);

  double voltage = 5 / 1024.0 * measure; //Digital to Analog conversion
  Serial.print("\tVoltage: ");
  Serial.print(voltage, 3);

  //PH_step = (voltage@PH7 - voltage@PH4) / (PH7 - PH4)
  //PH_probe = PH7 - ((voltage@PH7 - voltage@probe) / PH_step)
  float Po = 7 + ((2.5 - voltage) / 0.173);
  Serial.print("\tPH: ");
  Serial.print(Po, 3);

  Serial.println("");
  delay(100);
}

Most probes take that long or even longer to stabilise.

@Mvrale

Thank you very much for the advice.
I let my probe sit for 20 minuets and the readings seemed to stabilize.

Hi All

Just bought an Arduino due that has a maximum input voltage of 3.3v, I thought the 12 bit Dac would be a bonus.
I'm guessing that there is a high chance that I could exceed the 3.3v and blow the Due,
do I need to put a 3.3v voltage regular inline to stop me blowing up the arduino?

I'm only interested in between PH6 and PH 8

Thanks

Use a voltage divider instead.

Use quality resistors for this - especially with low temperature coefficient (50 ppm or better) or your measurements will be very off when the temperature changes (this doesn't negate the temperature correction on the pH reading itself).

Hi all
Veey interesting thread!

Which probe did you guys use?
There seems to be two types on ebay..a black and a bluish coloured one!
Any comments on those?

I got (separately) an "industrial" type probe, which is designed to be in the liquid constantly. Good change the probes you see on eBay are "lab" type probes, those can not remain in the liquid you want to test all the time. Check the description!

wvmarle:
I got (separately) an "industrial" type probe, which is designed to be in the liquid constantly. Good change the probes you see on eBay are "lab" type probes, those can not remain in the liquid you want to test all the time. Check the description!

I didn't see any note on the description that it is not designed to remain in the liquid all the time.
But yes, I intend to use it to constantly monitor he Ph of my pool water.

Which probe did you buy ?

No brand... got an inexpensive one off Taobao.

wvmarle:
No brand... got an inexpensive one off Taobao.

Care to share the link ?

https://item.taobao.com/item.htm?spm=a1z0k.6846577.1997989141.5.219937dexP9meN&id=520287697860&_u=

This one.
Haven't been able to verify it against calibrated probes but it seems to do the job quite well.

I'm in the process of building my own pH amplifier (designed to amplify in the 0-1V range, instead of the 2-3V range that this pH sensor board does - that way it can be read using the internal reference for much higher resolution and accuracy). When that's done I'll be doing more thorough testing as well.

Opps..its all in chinese!

I try to do Google translation but it didn't work. I am not even able to complete a purchase! :confused:

Yes... that's Taobao. Only Chinese.

They have international shipping methods (I routinely buy from that site - shipping to Hong Kong) but you have to be able to manage the Chinese part. Google Translate helps, for everything else there's the missus :slight_smile:

Aliexpress is the international version of Taobao.