Tower crane wireless remote control system based on MSP430 and nRF905

0 Introduction

The market for wireless telemetry products is developing rapidly, and wireless telemetry technology has become an important factor in determining product competitiveness. From a development perspective, wireless tower crane products are an inevitable trend. At present, most tower cranes used in domestic construction engineering and other industries are controlled by control rooms. Factors such as control room constraints, unclear vision, harsh environment or improper command and coordination can all pose potential safety hazards. Similar foreign products are too expensive and are mostly general-purpose products. However, there are many types of tower cranes used by a large number of small and medium-sized construction companies in my country. It is difficult to carry out remote control transformation based on the relevant technical information (mechanical and electrical schematics, working mechanism schematics, etc.) proposed by users, and then select the best control solution based on actual needs, which is not suitable for the characteristics of my country's market demand.

On the basis of the existing tower crane control room control, combined with microcomputer control technology, this study proposes a tower crane wireless remote control system with low power consumption, automatic CRC check code, software encoding and hardware decoding, memoryless control of the receiver, high anti-interference ability and high reliability, which not only ensures safe operation but also greatly improves production efficiency.

1 System Structure and Function Overview

The new tower crane wireless remote control system consists of two parts: a transmitter and a receiver. The structure of the remote control system is shown in Figure 1. The transmitter is composed of a keyboard input circuit, a single-chip microcomputer, a wireless transmission circuit, and an antenna; the receiver is composed of a receiving antenna, a wireless receiving circuit, a single-chip microcomputer, a 3:2:8 decoder, an inverter, a NAND gate, a photocoupler, a relay, etc. Its characteristic is that the core of the system adopts an ultra-low power MSP430 series single-chip microcomputer, and then adopts a 3:2:8 decoder, an inverter, a NAND gate, and a photocoupler to improve the anti-interference ability and system reliability.

Figure 1 System structure 2 System hardware circuit design

2.1 Transmitter circuit

The signal transmission circuit includes keyboard, CPU and data transmission part, and the hardware principle is shown in Figure 2. The control quantity of the tower crane (up, down, left, right, front, back, low speed, medium speed, high speed, emergency stop, etc.) is sent to the I/O port of the single-chip microcomputer MSP430F135 through the keyboard input circuit. The signal processed by the single-chip microcomputer is output to the wireless chip nRF905 through its SP I port. The single-chip microcomputer coordinates the normal operation of the entire system, and sets the radio frequency chip to determine its working mode, working frequency, transmission rate and other parameters. The output signal is processed by the wireless chip and sent to the wireless transmission part to the receiver.

The MSP430 microcontroller is an ultra-low power mixed signal controller produced by TI. These microcontrollers can be operated by batteries and have a long service life. The device can quickly wake up from low power mode in less than 6μs. The MSP430 microcontroller also integrates modules such as A/D converters, hardware multipliers, timers, and comparators.

Figure 2 Transmitter hardware schematic

The transmitting part uses nRF905 chip. nRF905 is a single-chip RF transceiver launched by Nordic Company of Norway. The operating voltage is 1.9~3.6 V, 32-pin QFN package (5 mm × 5 mm), and it works in 433/868/915 MHz three ISM channels. nRF905 consists of frequency synthesizer, receiving demodulator, power amplifier, crystal oscillator and modulator. It does not require an external SAW filter, ShockBurstTM working mode, automatically processes the header CRC (cyclic redundancy check), and uses the SPI interface to communicate with the microcontroller, which is very convenient to configure. In addition, its power consumption is very low. When transmitting with an output power of 10 dBm, the current is only 11 mA, and when working in the receiving mode, the current is 12.5 mA. It has built-in idle mode and shutdown mode, which is easy to achieve energy saving. nRF905 provides a powerful frequency hopping mechanism and a large number of channel support, which can be applied to many special occasions.

2.2 Receiving Circuit

The receiving circuit is basically the same as the transmitting circuit, except that the wireless chip works in the receiving mode. The tower crane system has high reliability requirements. In order to prevent interference from causing malfunction of the receiving circuit, the receiving drive output adopts software coding and hardware decoding technology, that is, the action of each relay corresponds to a digital code, which is decoded and output by the decoder, and the output signal is isolated by the optical coupler and driven by the inverter to output the control relay action. In this way, the output of other signals will be prohibited, and the system will also eliminate malfunctions caused by uncertain I/O port output during the short period of power-on (or power-off). [page]

3 System Software Design

The system software includes the transmitter and receiver software. The functional division of the transmitter and receiver software has a great impact on the performance of the remote control system. In order to improve the system reliability and speed up the recovery speed when an emergency failure occurs, all control logic processing is implemented in the transmitter. The transmitter uses two modes of transmission: timed transmission and interrupt transmission: when there is a button action, it is sent in interrupt mode, and in the following time, it is sent in timed mode. The receiver only realizes signal reception, decoding and drive output. When no information is received for three consecutive times, the receiver automatically turns off all outputs and returns to the initial state. The advantages of this are:

(1) The capture of the transmitter's button control is reliable. If the interrupt signal is lost, the receiver loses control and remains in the original state, but the subsequent scheduled control information will make corresponding controls.

(2) When the RF signal is interfered or the transmitter fails and the receiver cannot receive the control information, the receiver automatically turns off all outputs and returns to the initial state to prevent the accident from expanding. At the same time, it can also achieve "when the transmitter is turned off or the power is insufficient, the receiver automatically shuts down."

3.1 Transmitter software

When the transmitter is just powered on, the initialization completed mainly includes: I/O port initialization, wireless chip configuration, timer opening and I/O interrupt enable. The remaining functions are mainly implemented in the timer interrupt and I/O interrupt service subroutines. The main functions of the interrupt service subroutine are: judging the status of each button, button status encoding, and encoding status sending. The processing flow of the MSP430 microcontroller and nRF905 communicating through the SP I port is as follows:

(1) When the microcontroller has data to send, it transmits the receiver address and the data to be sent to nRF905 through the SP I interface in sequence;

(2) The microcontroller sets TRX_CE and TX_EN high to activate the ShockBurstTM transmission mode of nRF905.

(3) nRF905 sends according to ShockBurstTM: ① The RF register is automatically turned on; ② Data is packaged (with header and CRC checksum); ③ The data packet is sent; ④ When the data transmission is completed, the data ready pin is set high.

(4) AUTO_RETRAN is set high, and nRF905 continues to retransmit until TRX_CE is set low;

(5) When TRX_CE is set low, the nRF905 transmission process is completed and it automatically enters standby mode.

The transmitter flow chart is shown in Figure 3.

Figure 3 Transmitter main program flow chart

3.2 Receiver software

The receiver power-on initialization mainly includes: I/O port initialization, wireless chip configuration, opening timer and I/O interrupt enable, relay output enable. The rest of the functions are mainly implemented in the I/O interrupt service subroutine. After nRF905 enters the receiving mode, it continuously monitors the received signal. When the carrier signal is received, a CD interrupt signal is issued; when the received address is correct, an AM interrupt signal is issued; when the received data is correct, nRF905 automatically removes the header, address and CRC check bits, and then sets the data ready pin high to issue a DR interrupt signal. The main functions realized by the microcontroller interrupt service subroutine through the SP I port reading are: judging the status of each button, button status encoding, and encoding status sending. The MSP430 microcontroller reads the data in nRF905 through the SP I port, and the main program flow chart of the receiving end is shown in Figure 4.

Figure 4 Receiver main program flow chart

4 Conclusion

This system uses the ultra-low power MSP430 microcontroller and the low power wireless transceiver chip nRF905 to realize the wireless remote control system of the tower crane. The system adopts software encoding and hardware decoding, the system transmitter adopts timed scanning, the receiver adopts memoryless output control and electrical interlocking technology, which improves the reliability and anti-interference ability of the system. The system can be widely used in general industrial remote control systems such as tower cranes, and the functions of the system have been applied and verified in practice.