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Microcontroller-based multi-channel wireless temperature measurement system

In Electronic Infomation Category: M | on April 23,2011

Temperature in human daily life plays a very important role, both in the industrial and LC4256V-75F256B-10I datasheet and agricultural production process, the temperature measurement is of great significance. Cable temperature measurement at this stage is mainly fixed temperature detection, the temperature detection principle for the microcontroller using temperature sensors to detect temperature, and LC4256V-75F256B-10I price and tube or LCD on the digital temperature display. And because there is no alarm system, it is necessary to determine the need for artificial heating or cooling, which makes the system real-time detection of loss. In addition, in some environments harsh industrial environments, direct manipulation manually set the instrument measuring the temperature is not realistic, so the temperature detected by wireless is particularly necessary.

Present some design to achieve wireless temperature collection, but the power is too high is its greatest weakness. In practice, the process temperature control system has the stability of both the requirements, real time, and LC4256V-75F256B-10I suppliers and low power consumption and the need to ensure uniformity of temperature, so the design of a low-power wireless temperature measurement system more meaningful. This paper presents a low-power MCU MSP430F149 MCU multi-point wireless temperature measurement system to solve the above problem. The system can realize intelligent temperature detection, can simultaneously detect multi-point temperature, is a wireless remote control the temperature detection system. Low-power, real-time wireless temperature measurement is the largest of the design features.

1 System Components

System is divided into lower computer, PC and PC-three parts. PC, the top level of the entire system, responsible for the lower machine control and management, and each node to collect data storage and processing. As the next-bit machine can not communicate directly with the PC machine, which requires the host computer as the intermediary. Host computer and the next crew module through wireless communication, and the PC, using a wired connection. The design uses

MSP430F149 microcontroller as a core module, its main features lower power consumption. MSP430F149 features dual serial ports, one serial port using PC, communicating with, to pass between the RS 232 level converter chip. NRF24L01 microcontroller and wireless transmitter module can be through a common communications I / O port simulation of serial communication. Field temperature data collection is the use of NT C100 thermistor and the Ministry of MSP430F149 microcontroller with 12-bit A / D converter to achieve. There is no need external ADC, the circuit can be simplified to improve the system stability. The key input module, used to change the upper and lower temperature alarm. Since the design did not require too much content is displayed, taking into account power consumption and cost, can be made a simple code segment LCD displays. Machine design and lower overall system block diagram form in Figure 1, respectively, as shown in Figure 2.

Figure 1, lower computer design program

Figure 2, the overall composition of the system

2 Hardware Design

2. 1 wireless communication module design

NRF24L01 is a new single-chip radio transceiver devices, operating in 2. 4 ~ 2. 5 GHz ISM band. Built-in frequency synthesizer, power amplifier, crystal oscillator, modulator and other functional modules, and integration of the enhanced ShockBurst technology, in which the output power and communication channels can be configured by the program. nRF24L01 low power consumption, a variety of low-power mode (power-down mode and Idle mode) to make energy-saving design is more convenient for its application in Figure 3 circuit.

Figure 3 NRF24L01 Application Circuit

From the SCM point of view, just to the left of Figure 3, 6 control and data signals with the MCU general I / O port is connected.

2. 2 Temperature acquisition circuit

Order to lower overall system power consumption, low power consumption and MSP430149 thermistor NT C100 comes with an internal 12-bit A / D converter to achieve the temperature of the acquisition. The theoretical analysis and calculation of resistance and temperature relationship.

Where: RT is the temperature T (unit: K) when the NTC thermistor resistance; RN rated temperature TN (unit: K) when the NTC thermistor resistance; T for the prescribed temperature (unit: K); B for the NTC thermistor material constant, also known as thermal index.

Normal temperature environment, the temperature is 28 , converted into Kelvin temperature of 273. 15 + 28 = 301. 15 K. Measured by repeated 28 and 30 environment data, such as shown in Table 1, averaged, to minimize the error, considered B value.

Table 1 B values ??of thermal resistance measurement NTC100

By equation (1) available, the T, TN is converted into Kelvin temperature calculated B = 4 064. 34. After comparison found that the resistance obtained with the measured resistance is very similar.

Figure 4 shows the temperature acquisition module, which is the thermal resistance of R 1, R3 is 200 k resistor, R2 is 0 ~ 20 k, adjustable resistance, used to adjust the thermometer for accuracy. U0 for the detection of the voltage, the microcontroller pin U0 received, through the A / D conversion, the voltage will be converted into a temperature value displayed on the LCD.

Figure 4 Temperature acquisition module

2. 3 Display Module

Made this design uses 16-bit code segment LCD display. Using the LCD driver IC (HT 1621) and liquid crystal LCD glass supporting, self-made LCD 16-bit code segment. In addition, the driver IC is equipped with a buzzer drive circuit of two frequencies can be achieved alarm.

2. 4 serial communication module

The temperature acquisition process, because the system needs to be collected at any time the temperature value of the VC through the PC, the interface to display, PC, and therefore need to communicate with each other between the microcontroller. Because PC-RS 232 TTL level and the level of different microcontroller, hence the MAX3232 chip level conversion, this can be achieved between the MCU and PC machines communicate with each other.

3 Software Design

Software design is modular in design methods. Lower computer use timer interrupt to send the temperature data, the use of the port interrupt the upper and lower temperature alarm settings, other times in the low-power mode 3 of the state, which can significantly reduce power consumption. Interrupt the host computer receives data from receiver, and the use of MAX3232 with PC computer communication.

NTC thermistor is the main disadvantage of the nonlinear thermal characteristics of serious, this design uses a look-up table for NT C thermistor linearization. Linear interpolation software flow shown in Figure 5.

Figure 5 Linear interpolation of nonlinear self-tuning procedure thermistor flow chart

Figure 5, 0, R1, R2,, RK value is the abscissa of the curve; 0, T1, T2,, TK is the corresponding ordinate. K values ??can be determined according to the required temperature accuracy. Temperature T of the expression is:

4 test results and analysis

4. 1 temperature acquisition and display

Microcontroller write a program, even the good hardware circuits, using the keyboard on the lower set temperature, the microcontroller began collecting temperature data. Shown in Figure 6, is lower computer display interface, LCD display upper and lower limit alarm temperature, current temperature, and lower computer code.

Figure 6 shows the lower computer interface

After several tests, the temperature of the LCD display compared with ordinary thermometers to get the data in Table 2.

Table 2 LCD displays the temperature and normal temperature thermometer comparison tables

Tested, the temperature error is within the permissible range, the system can run stable. When the temperature data collected over the upper and lower limit set, the microcontroller will send alarm signal to remind users to temperature control.

4. 2 Power Test

Current crew entered LPM3 (sleep) mode, LCD does not display, but the internal clock is still running the string into the current meter, measuring current values, the measured current of about 4 uA. Proof system is very well ultra-low power consumption.

4. 3 wireless module tests

Connected to the wireless module, the first one on one send and receive debugging.

To lower computer 1 controls the wireless transceiver module to send a series of regular number of observations received digital host computer. After testing, 3-way controller system can be stable with the host computer send and receive one on one. Then three lower machine communication with the host computer, for sending and receiving a pair of three debugging, the host computer receives 3-way data, and display.

Tested, 3-way work can be normal, and low bit error rate, stable. Wireless module nRF24L01 the maximum transmission distance of about 100 m.

4. 4 VC interface display

First connection to the host computers hardware, the connection is initialized after power-on and open the PC-VC interface. When the normal VC interface is opened, there will be "open port" message; when the VC interface can not open properly, there will be "the serial port can not open" message, this is the case when the first test the hardware connection, and then check the serial channel selection is correct.

PC machine finally show in Figure 7.

Figure 7 PC machine shown in Figure

5 Concluding Remarks

This paper describes the MSP430 microcontroller-based wireless temperature control system software and hardware design. Proof system is operating normally through the debugger, the indicators can meet the design requirements. The whole system is highly integrated, low power consumption, temperature acquisition and wireless transmission speed, low error, and the small size, light weight, high reliability, easy to control and use the advantages of flexibility, and thus cost-effective.

Temperature accuracy of this design is 0. 5 , can further improve the accuracy of the actual demand; base stations in order to achieve power storage, the data can be stored in the microcontroller FLASH, FLASH when the power is removed from the need microcontroller values ??to display.

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