Please help with ph probe

Other Hardware Sensors
1

Hi
I am having a little trouble calibrating my new ph probe, and could please use a little help. First off let me say I am a software developer by day, and just trying to learn electronics, so I have a little tech experiance.

I have purchased this probe.

As part of this I also picked up one of these

I have wired it up like so:
V+ => 5v
G => G
Po => Ao

I have read this article, which states that as part of calibration, you need to short the sensor by poking a wire into the BNC connector and touching the outside. You can then use the offset pot to calibrate the value to 2.5v However when using the sketch in the article the lowest I can get the value when tunring the pot is 4.1

Here is the sketch I am using:

const int adcPin = A0;

void setup() {
  Serial.begin(115200);
}

void loop() {
  int adcValue = analogRead(adcPin);
  float phVoltage = (float)adcValue * 5.0 / 1024;
  Serial.print("ADC = "); Serial.print(adcValue);
  Serial.print(";  Po  = "); Serial.println(phVoltage, 3);
  delay(1000);
}

Am I missing something? At first I thought it could be a problem with the probe so I purchased another and that is the same. Did I get 2 broken items, or am I doing something wrong (more likley :slight_smile: )

Thanks for any help!

2

Measure the value with a voltmeter, not math. When the voltmeter says 2.5V, THEN look at what the AI is producing.

3

What is the EXACT voltage of the 5 volts you are feeding the sensor?

4

Hi,
Can you please post a circuit diagram?
Can you please post a image(s) of your project so we can see your component layout?

What model arduino are you using?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

5

Sorry for the late reply, I was waiting for a multimeter to be delivered, I also ordered an Arduino Uno as another device to test against (I was using a Wemos D1) When using the Arduino I get the correct values, however it seems when using the Wemos I get something different?

6

Hi,

Have you allowed for the fact that the Wemos is 3V3 device and the UNO is 5V?

Can you please post a circuit diagram?

Tom... :smiley: :+1: :coffee: :australia:

7

Thanks for your reply,
Here is a diagram (sorry if it rough)

image
image1015×706 18.3 KB

8

Seems after more reading the input for the WeMos is 3.3v and the output for the ph Probe is 5v. Is there a way to scale this is code?

9

No. These are hardware voltage limits, not something you can fix in software.

10

Use a 180k resistor between sensor output and A0
That will change the voltage divider already present on the WeMos to accept 0-5volt.
Leo..

11

Great thanks will try this!!

12

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