Software and hardware system design of DMX512 dimming equipment using ARM Cortex-M01 processor

1 Introduction

The DMX512 protocol is a digital multiplexing protocol developed by the United-States Institute for Theater Technology (USITT). Its original intention was to make the numerous dimmers and controllers used in stages, theaters, etc. compatible with each other. Although it is not an industry or national standard, it has been generally recognized by manufacturers and users around the world since its introduction due to its simplicity and practicality. In China, more and more manufacturers are producing or paying attention to digital dimming equipment using the DMX512 protocol.

This paper proposes a design of a DMX512 dimming device based on the Cortex-M0 microcontroller. This solution can access 2 DMX signals, merge them for dimming, detect the silicon circuit temperature, voltage and current according to the internal AD, and then report them to the console.

2.Cortex-M0

The ARM Cortex-M01 processor is the smallest, lowest energy consumption and most energy efficient ARM processor currently available. The processor has a very small silicon area, extremely low energy consumption and requires very little code. It is a 32-bit RISC processor with a 16-bit Thumb instruction set and high code density. The highly optimized power consumption and area make it more suitable for low-cost and low-power occasions. The automatic protection of the interrupt site minimizes the software overhead when entering and exiting the interrupt. At the same time, it has a certain instruction execution time to ensure that the execution time of each instruction is always the same, so as to achieve a real-time control. As the lowest-end product of ARM, it also has the characteristics of high cost performance, stability and reliability. Therefore, choosing this chip and applying ARM's MDK integrated development tool can improve development efficiency and shorten the development cycle.

3. System hardware design

This DMX512 dimming device is based on NUC100 (Cortex-M0) as the control core. The hardware part of the whole system includes DMX512 signal access module, MCU, phase detection module, dimming output module, temperature, voltage and current detection module, communication module, display module, etc. The block diagram of the whole DMX512 dimming device is shown in Figure 1.

The essence of DMX512 signal is RS485 signal, so it can meet the requirements by connecting through the serial port of NUC100 and adding 485 chip. The temperature and current detection module converts the temperature and current into corresponding voltage signals through the peripheral current and samples them through the AD channel of NUC100. The phase detection module correctly detects the zero crossing point of the AC power through the LM258 comparator. The dimming output module outputs PWM signal from NUC100 to control the silicon block to control the light intensity. The communication module can report the real-time detected temperature and current to the console through the serial port, and the console can set the device through this interface. The hardware block diagram of the entire device is shown in Figure 2 below.

4. System software design

The software part adopts program modular design to facilitate the debugging and implementation of various functions. The system software program mainly consists of five modules: main program, Dmx512 signal processing, dimming control PWM output processing, communication processing, and display processing.

4.1 Main program module

The main program module uses a loop query until the power is cut off to exit, so as to achieve the purpose of controlling the brightness of the light. The main program flow is shown in Figure 3.

4.2 Dmx512 signal processing module

The DMX512 signal processing module receives the DMX512 signal from the outside. After receiving the break signal, it starts to receive data. After receiving the next break signal, the reception of one frame of DMX512 data is completed. The DMX512 data reception process is shown in Figure 4.

4.3 Dimming Control PWM Output Processing Module

The PWM output processing module outputs a PWM signal with a period of 10ms according to the DMX512 data. Figure 5 shows the PWM dimming output process.

4.4 Communication Processing Module

The communication processing module processes the signals from the console and performs equipment initialization, configuration, and debugging.

4.5 Display Processing Module

The display processing module is responsible for displaying the start address of the display device using the DMX512 signal.

5. Conclusion

This paper proposes a design scheme of DMX512 dimming device based on Cortex-M0. The scheme is based on 485 serial communication technology, and from the application perspective, the hardware and software design of DMX512 dimming adjustment is given. Practical application proves that the device is easy to operate, runs well, and has stable and reliable functions.