Design of control system for flying saucer-shaped colorful LED landscape water mist machine

A water mist machine is a device that turns water into mist, which has the functions of increasing humidity, purifying air, and beautifying the environment. At present, due to the limitations of materials and technology, the amount of mist produced and the concentration of water mist in the artificial mist systems in the domestic and foreign markets are difficult to achieve the ideal effect. The mist is generally thin, and once the nozzle is fixed, the mist shape is fixed accordingly [1]. If you want to change the shape or scattering surface of the mist, you need to replace the nozzle.

In comparison, the water mist area formed by a single UFO-type water mist machine has a scattering diameter of 30 m~50 m and a thickness of 0.5 m~2 m. It has sufficient mist volume and great momentum, and can flexibly adjust different mist landscapes according to different usage environment requirements. The mist production of a single machine is equivalent to the mist production of 350~450 nozzles in the current artificial fog system on the market.

1 Basic principles

At present, the working principle of artificial fog systems in the domestic and foreign markets is similar to that of sprinkler irrigation systems. It mainly pressurizes ordinary tap water through a high-pressure unit, then transports the water to the fog-making site through a dedicated high-pressure (7 MPa~30 MPa) distribution pipeline, and finally uses a high-pressure nozzle to convert the water into fog [2]. The only difference is the atomization effect of the nozzle, working pressure and equipment performance.

In comparison, the UFO-type landscape water mist machine is a large-scale fog machine widely used indoors and outdoors, with low water and electricity consumption, energy saving and environmental protection. Its atomization working principle is to input low-pressure air (0.75 MPa~1 MPa), and under the effective control of the air valve and water valve by the control system, the water is instantly split into micron-sized water mist particles by the machine's internal core device, and then ejected from the nozzle, dispersed over a large area and suspended in the air, thus forming a huge water mist landscape with excellent indoor and outdoor viewing [3].

2 Control system design

2.1 Hardware System Design

Based on the principles of simplicity, practicality and reliability, this system uses AT 51S series microcontroller as the control core, which mainly includes four parts: input interface circuit, output control interface circuit, LED drive circuit and communication interface circuit design.

Input signal detection: This part is mainly for water level detection and day and night detection.

The water mist machine works in a pre-water storage mode and is equipped with a small water tank inside. Before spraying, make sure that the water tank is filled with water. A Hall-type float level sensor is selected for liquid level control. The sensor is sensitive and has a stable output signal, which can ensure timely output of water shortage and water fullness signals for the mainboard to collect.

The day and night detection uses the commonly used control method of photoresistor plus Schmitt trigger. By adjusting the adjustable precision resistor, the light sensing intensity is set to output the "day and night" control signal. The purpose of day and night detection is mainly to control the colorful LED lights, turning them off during the day and turning them on at night.

Output control: The output control of the atomizer is mainly the control of the air valve and the water valve. The water valve control is to open or close the water valve in time according to the input signal of the liquid level switch to prepare the water storage before spraying. The air valve control is to open at a predetermined time according to the system settings, input low-pressure air into the core of the atomizer for spraying, and close at a predetermined time to achieve intermittent cycle spraying. This part of the circuit uses thyristor BTA06 as the main control element, as shown in Figure 1. The DCF-WTR in the figure is an output pin of the microcontroller, indicating the control of the water valve. The control circuit of the air valve is the same.

LED drive circuit: This system is designed to install 30 small colorful LED lights, which are evenly distributed on the upper spherical surface of the flying saucer together with 28 nozzles; there are 12 colorful LED spotlights, 6 on the upper disc surface and 6 on the lower disc surface. Each lamp is composed of multiple LEDs in red (R), green (G), and blue (B) colors connected in series and parallel. The main control board is designed with 8 small colorful lamp holders and 8 colorful spotlight holders. Each lamp holder can connect up to 4 lamps in parallel. Since each lamp is composed of three colors, R, G, and B, 8 lamp holders require 3 8-bit ports, plus 8 spotlight holders, so a total of 6 8-bit ports are required. The P0 port of the microcontroller is used as the basic port for LED driving, and parallel expansion is carried out through a 3-8 decoder [4]. In this way, each lamp holder will have a certain control address.

Communication interface circuit: In order to facilitate the unified coordination and control of multiple water mist machines through the host computer and achieve the dynamic spray effect of the landscape site, this system reserves the RS-485 bus interface circuit, as shown in Figure 2. The interface uses the 75176 communication chip and realizes automatic transceiver conversion through the transistor 9014 [5], which simplifies the programming. Two 1 kΩ and one 510 Ω resistors are used on the data line to ensure normal transmission and reception and enhance the system's anti-interference ability.

2.2 Control software design

2.2.1 Control algorithm design

Since program-controlled water mist machines are generally distributed in multiple units in a square and controlled in linkage, a linkage control scheme needs to be set up in the absence of unified coordination and control by the host computer (i.e., offline state). The requirements are as follows: A scenic spot can be equipped with several water mist machines. According to the actual situation on site, these machines can be divided into up to 40 groups (1 to 3 machines per group). The mist machines in the same group spray at the same time at the set time, and each spray lasts 2 minutes. After the water mist machine of the adjacent group has finished spraying, it waits for 1 minute and then starts spraying, and so on. In addition, when powered on for the first time, it is necessary to fill the water tank of the water mist machine with water. It can only spray after the water is full. The pre-water filling time is set to 6 minutes.

According to the above analysis, the timer allocation of the microcontroller during programming is as follows:

T0: used to detect the photosensor and water tank liquid level height signal;
T1: used for spray timing, that is, close the air valve after 2 minutes to stop spraying, with 5 seconds as the minimum timing unit;
T2: used for delay timing before spraying, with 0.5 minutes as the minimum timing unit. The first power-on delay is TS minutes, and spraying is performed every TF minutes thereafter.

2.2.2 Software Process Design

The essence of the system control software is to accurately control the start and stop time of the spray, so the design of the timer interrupt service program is the focus of this program, and the task of the main program is relatively simple, which is to control the alternating changes of the seven-color lights. If it is daytime, turn off all lights; if it is night, turn on the lights. The main program flow is shown in Figure 4.

According to the allocation of the above timers, the service programs of T1 and T2 are the focus of compilation. Since the selected crystal oscillators are different, the clock cycles are also different. In order to achieve precise control, the relevant delay constants must be accurately calculated according to the specific crystal oscillator frequency [6]. The program of the T1 timer is relatively simple. As long as the time reaches 2 minutes, the output control closes the air valve to stop the spraying. At the same time, the volume of the background music is appropriately reduced to adapt to the surrounding environment.

After the T2 timer enters the interrupt, in addition to the conventional on-site protection, it is also necessary to determine whether this interrupt is the first power-on interrupt, which involves whether to use TS or TF for the delay before spraying. If the timing is up, the output control opens the air valve and starts spraying, while appropriately increasing the volume of the background music to enhance the atmosphere of the landscape; if the timing is not up, the scene is restored and the interrupt service program is exited. The specific process is shown in Figure 5.

The system has become an actual product, filling the domestic gap, and has important applications in many aspects such as dust removal, irrigation, anti-static, and regulating the climate of the community, while also beautifying the environment. Practical application has proved that the system has precise control, is stable and reliable, is environmentally friendly and energy-saving, and can be mass-produced and promoted.