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Summary Of Progress Up To CA2
 Max Ng Zhen Qiang
NUS Electrical Engineering Year 4

Ambient Media In The Digital World 


The following researchs have been done to obtain a better understanding on the system that we are going to build.


The system consist of a few major parts. The pH meter, the pH control system and humanistic organic information. The pH meter is built by Chris and i assisted him in the PCB fabrications. The pH control system is being built by me and Chris assisted with the programming. Currently both subsystem has been fully implemented on PCB boards with resistor of tolerance ±1%. However there is still some minor adjustments that need to be done.

The pH control system will be explained in greater details in the next section. Only when both subsystem is done, then we can move on to the input for the system.

pH Control System

After experimenting and testing, the figure below shows the most updated version of the pH control system. 
It is possible to control pH digitally using electronic valves and various solutions(acidic, basic and distilled water). The schematic diagram is shown above. The valves work in such a way that when a voltage is pass through the gate, the valves which is normally closed, will open and allow the solution to flow through it. To lower the pH of the solution(make it more acidic), voltage can be past through the valves containing the acidic solution to allow it to flow through and mix with the solution making it more acidic. Likewise for increasing the pH, basic solution can be added. The purpose of distilled water is to dilute the solution. For example if i want to increase the pH of the solution from 5 to 6, i can just add water instead of a base to increase the pH. This is to prevent the formation of salts. The drain is used to keep the volume of the solution constant to prevent overflowing.

Control System The control system works in the way that when a set point is being entered (ie. a change in humanistic information), the system will check whether the pH is greater or lesser than the set point. Then it will release the correct solution to change the pH. It will wait till the pH of the solution reaches the set point then it will close the valve. If there is overshoot, which means that the pH went past the set point, the cycle repeats itself until the pH is stable. The above flow chart illustrates the process of the control system.

Program Interface

Actual System We Experimenting With

The two system that we are using now is in the picture shown below. The one on the left is made of glass and the other made of plastic. Both containers work very well and currently we are thinking of ways to make the display nicer. Problems With the Previous System

Solution to the problems

A tube can be used as a substitute in place of the draining valve. There should be an opening in the tube to prevent the tube from sucking all the water out. (Shown in figure above)

Schematics of Valves Circuit

PCB Drawing

Experiment and Testing of pH Meter

After the pH meter is fully implemented on the PCB with resistors of tolerance ±1%, it is being tested with commercial pH meter and commercial solutions. After some minor adjustments, we tested it with the commercial solutions to obtain the response time. The results are being illustrated in the charts below. 

Method Used

Solution Used The time response of the pH meter is plotted against the pH. Firstly the pH meter is being placed in a solution with pH 7, then it is being transferred to another solution with pH 4 and pH 10. Then the time for the pH to reach to ± 0.2 of the intended pH is then being noted.


From pH 7 to pH 10

Time taken to reach 0.2 of the intended pH = 3.42 - 2.58 = 0.84s

From pH 7 to pH 4

Time taken to reach 0.2 of the intended pH = 4 - 2.58 = 1.42s


Average time taken to change 3 pH level = 0.5(0.84 + 1.42) = 1.13s

Future Plans

After the system is done, the next part of the project is to bring in the feedback control. The purpose of the feedback control is the help the system reach a steady state pH in the shortest time possible. More research have to be done to understand the system and include a controller to help the system achieve the fastest settling time. page revision: 54, last edited: 29 Nov 2007 08:10
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