Design of wireless temperature measurement and control circuit based on LabVIEW

The temperature measurement and control system is mainly composed of a computer, a single-chip microcomputer, a temperature measurement circuit, a temperature control circuit and a wireless communication circuit. The TMPll2 temperature sensor collects the temperature, and after transmitting the temperature digital quantity to the P89LV51RD2, the on-site temperature is displayed through the digital tube LED circuit. At the same time, P89LV51RD2 sends the temperature data to the remote computer through the wireless communication module SZ05. The LabVIEW control platform running on the PC displays the temperature in real time, and performs data processing, temperature alarm and data storage. In addition, the control platform samples the input signal, uses the PID controller in LabVIEW for PID control, and sends the control value to the microcontroller through the wireless module. The microcontroller outputs the control value to achieve temperature control.

temperature control circuit

The temperature control circuit is shown in Figure 2. It is mainly composed of NPN transistor Q1, TLP521-1 photocoupler U1 and high-power NMOS tube Q2. The host computer program control system compares the detected temperature value with the system setting value, performs calculations according to the PID control algorithm, and outputs a PWM signal with an adjustable duty cycle from the P1.2 port of the microcontroller. After being driven by the transistor Q1, it controls the photoelectric coupling. The on-off time of the device U1 is controlled, and then the on-off time of the NMOS tube Q2 (IRF840A) is controlled, thereby controlling the heating time of the heating object - the high-power resistor R, so that it reaches the set temperature value. To facilitate the experiment, the R used is a high-power wire-wound resistor with a rated power of 10W and a rated resistance of 10Ω. It is powered by a +12V DC power supply. Since the current flowing through the heating resistor R is relatively large, the +12V DC power supply that powers R must be separated from the +12V DC power supply that powers other analog devices.

The temperature measurement and control system uses a low-power microcontroller system as the acquisition module, replacing the expensive data acquisition board, with low cost. It uses the software platform developed by LabVIEW for temperature processing and control. Compared with traditional instruments, it has a friendly interface and Easy to operate and highly scalable. This system can be used as part of the teaching experiment system and embedded in the virtual instrument experiment platform for students to learn LabVIEW programming and the communication between virtual instruments and microcontrollers. In addition, multiple nodes can be networked to form a distributed wireless network to achieve multi-point temperature measurement and control, which has good application prospects.