Analog PH Sensor Kit

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Description

The power of Hydrogen in any liquid can be measured with a total pH scale range of 0-14 where 7.0 is considered as a neutral value. The pH electrode has a single cylinder that allows direct connection to the input terminal of a pH meter, controller, or any pH device which has a BNC input terminal.
You can just connect the pH sensor with a BNC connector, and plug the PH2.0 interface into any analog input on the Arduino controller to read pH value easily but you have to calibrate it before use if the pH probe was kept long. Calibration can be done via software or using a potentiometer present on the device.

Specification
Heating Voltage 5V ± 0.2V DC/AC
Current 5-10mA
Detection concentration range PH0-14
Detection range of temperature 0-80°C
Response time ≤5s
Stability time ≤60s
Power consumption ≤0.5W
Working Temperature  -10~50°C
Working Humidity 95% RH
Service life 3 years
PCB Size 42mmx32mmx20mm
Output Analog voltage signal


Pinout

TO Temperature output
DO 3.3V pH limit trigger
PO pH analog output
GND GND for pH probe
GND GND for board
VCC  5V DC
POT1 Analog reading offset(Nearest to BNC connector)
POT2 pH limit setting

Further Resources

As we can observe that in the circuit there are two knobs. One which is near the BNC connector probe is the one that regulates the offset, the other is the limit of pH.

  • Offset: the mean (range) of the probe oscillates between negative and positive values. The 0 represents a pH of 7.0.since we are not reading from the electrode directly but from the voltage adapter, it has converted the original voltage (-5V ~ +5V) to Arduino compatible voltage, i.e. 0 ~ 5V
To be able to use it with Arduino, this circuit adds an offset value to the value measured by the probe, this way the ADC will only have to take a sample of positive values of voltage. Therefore we'll force a pH of 7.0 by disconnecting the probe from the circuit and short-circuit the inner part of the BNC connector with the outside. With a multimeter, we measure the value of the pin Po and adjust the potentiometer to 2.5V.
  • Limit of pH: This knob is for setting a limit value of the circuit for the pH sensor that makes the LED red turn on and the signal of pin Do is put on ON.

In addition, we need to calculate the conversion of the voltage that will give us the pH sensor to what we will need two reference values of pH and measuring the voltage returned by the sensor on the pin Po. It is better to use a solution for calibration. These solutions are sold in different values, although the most common are pH 4.01, pH 6.86, and pH 9.18.

Using the envelopes with pH 4.01 and pH 6.86 we obtain the voltages on the pin Po 3.04 V and 2.54 V, respectively. The sensor is linear so that by taking two points, we can deduce the equation to convert the measured voltage to pH. The formula overall would be y=mx+b, so we have to calculate m and b as x would be the voltage e and the pH. The result is y=-5.70 x+21.34.

Connection with Arduino

To connect it with Arduino, you will need an analog input (A0), power (5V), and two GND that in reality in the sensor circuit are separated but we can use the same.

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