WEEK 9: pH SENSOR Calibration

I've tried testing the pH sensor to see whether it able to produce a reading or not. The connection between the board and the pH sensor is as below:

CC3200 and pH module connection (fritzing)

A 10 k potentiometer is used to as a part of the calibration. The DATA pin of the pH module is connected to the potentiometer where the output from it is connected to the  to the analogRead pin 2 of the CC3200 board while the VCC and Ground pin is connected accordingly.

Before it can be use to measure the pH water, it needs to be calibrate first to ensure its accuracy. The calibration is divided into two part, which is the sensor module calibration and the probe calibration. For the sensor module calibration, the BNC part of the sensor module is short-circuit by using a stripped wire to simulate a neutral pH reading that is pH 7. The 10k potentiometer controls the output voltage to the analog pin of the microcontroller so that the output voltage from the is 2.5V the neutral state, pH 7. 

Short-circuit of the BNC connector

The pH probe is calibrated using the buffer solution. There is three buffer solution which the common buffer solution used are pH 4.01 and pH 6.86, as it applies to the range of most pH applications while the other one is pH 9.18. The buffer solution is made by adding the buffer powder to 250 ml of distilled water and stirred until dissolved.

Buffer powder

Replace the stripped wire with the probe, connect it to the sensor module and immersed the probe in the pH solution. The offset for the pH probe calibration is set at the coding on the Energia software based on the value of the pH displayed on the serial monitor. In example, if the reading on the serial monitor is pH 5.44 and the buffer solution is pH 6.86, change the offset value to 1.42.

Setting pH the pH probe offset