Design of wireless temperature acquisition and alarm system based on CC430F5137

introduction

With the continuous advancement of science and technology, modern production has continuously increased the requirements for real-time, high efficiency and low energy consumption of temperature acquisition. In addition, many on-site environments for measuring temperature are very harsh, making it difficult for operators to reach the site for measurement. In this regard, a temperature acquisition system that can automatically collect, process and transmit data wirelessly is needed. At the same time, in order to save the cost of use and maintenance, this system also needs to have the performance of long-term stable operation. Therefore, the development of a temperature acquisition system with low power consumption and wireless data transmission can make up for the defects in the current field of temperature acquisition.

Although the temperature acquisition system designed in the reference has low power consumption, it must be connected by line for communication, which greatly limits the application occasions and makes its application have certain limitations. The temperature acquisition system designed in the reference uses ZigBee wireless communication technology as a communication tool, but it must use a separate external ZigBee module to complete the communication function, so the production cost is relatively high. In view of the above shortcomings, the CC430F5137 chip used in this system not only has the low power consumption performance of the MSP430 series, but also has the function of RF wireless transceiver. These two performances fully meet the requirements of low power consumption and wireless communication, reduce the cost of the system, and meet the requirements of current applications.

1 Overall operation principle of the device

1.1 Device operation principle

The wireless temperature acquisition alarm system mainly consists of two parts, one is the temperature acquisition module, and the other is the central control module. The central control module includes a keyboard, display module and an alarm module. The overall block diagram of the system is shown in Figure 1. When the system is working, the temperature sensors in each temperature acquisition module first complete the temperature acquisition task, then the CC430F5137 microcontroller obtains the temperature parameters through the I/O port, and finally transmits the collected temperature information to the main controller system through the RF wireless transceiver integrated in the CC430F5137. The main control system systematically analyzes the temperature data collected from each site and displays the results using a digital tube. When the temperature exceeds the upper or lower limit, the alarm device is triggered, which is achieved by driving a buzzer and an alarm light. The upper and lower limits of the alarm temperature can be set through the keyboard input module. The main console has two groups of digital tubes, one group of digital tubes displays the serial number of the temperature acquisition module, and the serial number of the temperature acquisition module to be displayed can be selected through the keyboard, and the other group displays the temperature value.

2 System Hardware Design

The hardware design of the temperature acquisition alarm system includes the temperature acquisition module design and the central controller design.

2.1 Temperature acquisition module design

2.1.1 CC430F5137 Device Introduction

The CC430F5137 is a combination of the TI MSP430F5xx MCU and a low-power RF transceiver, which can achieve extremely low current consumption, allowing battery-powered wireless network applications to operate for more than 10 years without maintenance. In addition, the advanced features included in the tiny package can also provide the core power for innovative RF sensor networks to report data to a central collection point. The CC430 F5137 is a 16-bit ultra-low-power MCU with 16 KB flash, 2KB RAM, CC1101 radio, AES-128 and USCI. The supply voltage is 1.8 to 3.6 V, the normal operating mode consumes 160μA/MHz, and the low-power mode 3 consumes 2.0μA. [page]

2.1.2 CC430F5137 RF wireless transceiver module circuit design

CC430F5137 integrates CC1101 radio transceiver, RF frequency is 432.999817MHz, channel spacing is 199.951172kHz, data transmission rate is 38.383484kbps. In this system design, the wireless transmission power can be set. According to the distance of the transmission, the power can be set to the minimum, so as to achieve low power consumption. Its circuit diagram is shown in Figure 2. The power supply of CC430F5137 is two No. 7 batteries with a voltage of +3V. The external crystal oscillator is 26MHz. RF_N and RF_P are RF radio transmission pins. The two pins are connected to an external antenna. Its power can reach -30dBm and the transmission distance can reach about 100m.

2.1.3 Temperature acquisition circuit design

Considering the low power consumption requirement of the equipment, the selected temperature sensor must have low power consumption characteristics. Here, the MAX6613 integrated temperature sensor is selected. MAX6613 is a high-speed, high-precision, low-power temperature sensor, which is particularly suitable for low-power products. The power supply voltage range of MAX6613 is 1.8~5.5V; low power supply current consumption, typical value is 7.5μA; measurement range is -55~+130℃; nonlinear error is 1.3℃. The relationship between the measured temperature and the output voltage is:

Vout=-0.011 23T+1.8455Vref (1)

Where Vout is the output voltage of the sensor, T is the measured temperature, and Vref is the measured voltage of the sensor obtained by the reference voltage. The microcontroller collects the output voltage of the sensor through the analog acquisition port, and the actual measured temperature value can be calculated through formula (1). Because CC430F5137 has an internal integrated ADC module, its input voltage range is 0~3.6V, which can meet the requirements of the system, so the voltage output port of MAX6613 can be directly connected to the ADC input port of CC430F5137. The circuit diagram is shown in Figure 3.

2.2 Main Controller Design

The RF receiving and transmitting module of the main controller is configured the same as the RF receiving and transmitting module in the temperature acquisition module, which will not be described in detail here.

2.2.1 Alarm system hardware circuit design

The alarm system controls the on and off of the transistor to control the on and off of the buzzer and the alarm light, thereby achieving the purpose of the alarm.

The P2.0 port of the CC430F5137 microcontroller controls the conduction or cutoff of the transistor by controlling the high and low levels of the output signal, as shown in Figure 4. If the transistor is turned on, the buzzer will alarm and the alarm light will be turned on. When the measured temperature value exceeds the preset upper and lower temperature limits, the alarm system will be activated. When the temperature value is adjusted within the normal working range, the alarm system will automatically stop the alarm.

2.2.2 Keyboard and display module hardware circuit design

The keyboard adopts a 4×2 keyboard mode with a total of 8 keys. The function buttons are start button, stop button, function 1 upper limit temperature value setting button, function 2 lower limit temperature value setting button, function 3 temperature acquisition module serial number selection button, value plus 1, value minus 1, and manual alarm button.

CC430F5137 has 16 external interrupt I/O ports, namely P0 and P1. Here, P0 is used as the keyboard scan port. As long as a key is pressed, the corresponding two I/O ports will be set to low level. As long as it is determined which two I/O ports have interrupts, the pressed button can be determined and the corresponding operation can be performed.

2.2.3 Display module hardware circuit design

Considering the cost requirement, the display module uses digital tubes as the display interface, as shown in Figure 5. The system uses 8 digital tubes to display the temperature. The first 4 are a group to display the serial number of the temperature acquisition module; the last four are a group to display the temperature value collected by the temperature acquisition module, and the first digital tube is the sign bit. The system uses a 74HC245 bus driver to drive the corresponding LED digital tubes, and the P1 port is used as the chip select signal of the LED digital tube. [page]

3 System Software Design

The software design of the temperature acquisition alarm system includes the software design of the main controller and the temperature acquisition module.

3.1 Main controller software design

The program flow of the main controller is shown in Figure 6. First, press the start button to start the system. At this time, CC430F5137 will issue a control instruction to the specified temperature measurement module to start temperature acquisition. The specified temperature acquisition module will send the measured temperature data to the main controller (the system defaults to display the measurement data of the first temperature acquisition module). After receiving the data, the main controller starts to execute the display program. First, the serial number of the temperature acquisition module is displayed on the first group of digital tubes, and the temperature value is displayed on the second group. The main controller will continuously determine whether the temperature value exceeds the limit. If it exceeds the limit, the system will trigger the alarm device. At this time, the buzzer will sound and the alarm light will light up until the temperature value returns to the allowed range. If a key is pressed, the corresponding key function will be executed and sent to the specified temperature acquisition module.

3.2 Temperature acquisition module software programming

The program flow of the temperature acquisition module is shown in Figure 7. When the main controller sends a control instruction, the temperature acquisition module starts to receive the instruction and executes the corresponding instruction function. First, the CC430F5137 in the temperature acquisition module will collect the voltage signal output by the MAX6613, then calculate the corresponding temperature value and send it to the main controller. If no instruction is received, the system will not collect the voltage signal of the MAX6613, and the temperature acquisition module will always be in low power mode 3, which can reduce power consumption. In low power mode 3, the system's DC generator is turned off, only the crystal oscillator is active, and the system's total interrupt enable bit is turned on. If there is an RF wireless transceiver interrupt, the system will wake up from low power mode 3 and start executing the temperature detection program. In this way, power consumption can be minimized and low power consumption requirements can be met.

RF Radio Interrupt Subroutine:

Conclusion

This paper designs a wireless temperature acquisition alarm system based on CC430F5137. This module is mainly composed of a main controller and a temperature acquisition module. After testing, the system runs stably and reliably, but when the distance is far and there are obstacles in the middle of the transmission, the sent data will be lost. It needs to be continuously improved according to the actual application scenarios.