The Design Of PH Meter Based On MSP 430

Along with the people's recognition to the environmental protection the analysis of water quality is also one part that the people pay attention to gradually。So there are more requests to the checking equipment—pH meter. Because of being confined by the electronics technique and manufacture craft, the pH examination instrument is hard to be small,to be taken easily.The development of modern electronic technology and improvement of manufacture craft provide the possibility for many instrument to small scaled.This paper design is a machine that is the portable intelligent examination instrument based on signal chip micro-computer(SCM). Proposed a plan of realizing the survey of pH value and completed the hardware circuit and the software routine design.The hardware design may be divided into the metering circuit design and the microprocessor input output interface circuit design. According to the Electric potential survey law and the Nernst equation the pH value of the aqua is the function of the electric voltage and temperature, so when measuring the aqua temperature is also a very important factor. Based on the characteristic of the electrochemistry sensor, choose the appropriate sensor metering circuit, then according to the function that to be completed and the requirement of accuracy, design the functional modules of enlarge, filter, simulation quantity transformation and so on. There is a thermistor resistance in the pH electrochemistry sensor, the resistance number change reacts the temperature change, we make the resistance change transform to the voltage change to obtain this temperature value, and send it to the SCM for processing, then use it in displaying the current temperature and carrying on the temperature compensation; The output signal of the signal electrode and the reference electrode in the compound pH electrode is a voltage difference. Under certain temperature, so long as obtain the precise voltage value, then know the pH value of the solution. As the compound pH electrode interface resistance is very high, the key of metering circuit is realizing the high impedance input. In the paper we used the high-resistance magnifier, first level through using the cocurrent magnifier might obtain the high input impedance of T ohm level, the latter level uses the differentiator amplifier to be possible to obtain the high syntype rejection ratio, simultaneity intensifies the antijamming ability of the circuit. The data processing uses the MSP430F149 momolithic integrated circuit to be the platform, it has the low power loss merit and the rich periphery module, this may lengthen the use cycle of power supply battery and also make the electric circuit to be relatively simple.The major function of the software is to carry on the sampling input signal by MSP430F149 built-in A/D, analyse the sampling data, and display the accurate pH value and the temperature value of the measured solution. The electrode will aging with the increase of use number, therefore this paper used two-point proofreading method to carry on the adjustment for it. Based on the function to be realized by the pH-meter, the software work can be diveded into measurement, interrupt, the memory read-write procedure, data processing and so on parts. These funcions realize separately by certain sub-program module, each module realizes the specific duty independently.First, it introduces the task and way of ph test, analyzes the develop direction of the intelligent instrument. The way of designing the intelligent instrument is also discussed. And this paper analyzes the developing situation of ph meter.Secondly, it offers the design method of ph meter as a whole. The signal processing circuits and the software implementing of functions are also studied.Third, it expounds the theory of the chemic probe, temperature compensation and proofread process.Finally, according to above studies, we have developed an intelligent ph meter which has been tested and proved to perform well. We also found some disadvantages and gave corresponding solutions.