Design of solar lawn lamp based on 51 single chip microcomputer

As the earth's resources become increasingly scarce and the investment cost of basic energy sources increases, solar energy, as an inexhaustible, safe and environmentally friendly new energy source, is receiving more and more attention. Various types of solar landscape decoration products have also emerged. Solar lawn lights will also be widely used as people's living standards improve and society continues to develop. This article discusses the technical issues of the design and selection of the main components of solar lawn lights, and introduces a design scheme of a new type of solar lawn light based on a 51 single-chip microcomputer, as shown in Figure 1.


Figure 1 Solar lawn light

1 Selection of solar cells
1.1 Type
Solar energy cells convert solar energy into electrical energy. The more practical ones are single crystal silicon, polycrystalline silicon, and amorphous silicon solar cells.
① The performance parameters of single crystal silicon solar cells are relatively stable, and they are suitable for use in southern regions where there are more rainy days and not enough sunshine.
② The production process of polycrystalline silicon solar cells is relatively simple, and the price is lower than that of single crystal silicon. They are suitable for use in eastern and western regions with sufficient sunlight and good sunshine.
③ Amorphous silicon solar cells have relatively low requirements for sunlight conditions and are suitable for use in places where outdoor sunlight is insufficient.
1.2 Working voltage
The working voltage of solar cells should be 1.5 times the voltage of the matching battery to ensure normal charging of the battery. For example, a 4.0-5.4 V solar cell is needed to charge a 3.6 V battery; an 8-9 V solar cell is needed to charge a 6 V battery; and a 15-18 V solar cell is needed to charge a 12 V battery.
1.3 Output power
The output power per unit area of ​​a solar cell is about 127 Wp/m2. Solar cells are generally composed of multiple solar cell units connected in series, and their capacity depends on the total power consumed by the light source, line transmission components, and local solar radiation energy. The output power of the solar cell group should be 3-5 times higher than the power of the light source. In areas with abundant light and short lighting time, it should be (3-4) times or more; otherwise, it should be (4-5) times or more.
   
2 Selection of batteries
The battery stores the electrical energy generated by the solar panel when there is light, and releases it when lighting is needed at night.
2.1 Type selection
① Lead-acid (CS) battery: used for low-temperature high-rate discharge, low capacity, currently used by most solar street lights. Sealed maintenance-free, low price. But pay attention to prevent lead-acid pollution, should be gradually eliminated.
② Nickel-cadmium (Ni-Cd) battery: high discharge rate,
good low-temperature performance, long cycle life, small system use, but pay attention to prevent cadmium pollution.
③ Nickel-metal hydride (Ni-H) battery: high rate discharge, good low-temperature performance, cheap, pollution-free, green and environmentally friendly battery. Can be used for small systems, this product should be strongly promoted.
At present, there are three widely used lead-acid maintenance-free batteries, ordinary lead-acid batteries and alkaline nickel-cadmium batteries.
2.2 Battery connection
When connecting in parallel, consider the unbalanced effect between each single battery, and the number of parallel groups should not exceed four groups. Pay attention to the anti-theft problem of the battery during installation.

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3 Principle of the new solar lawn lamp circuit based on 51 single-chip microcomputer
In Figure 2, U18051 is an 8-bit single-chip microcontroller, which belongs to a type of MCS-51 single-chip and was manufactured by Intel in 1981. The U18051 single-chip is a synchronous sequential logic system. The operation of the entire system is completely dependent on the internal clock signal of the system to generate various action cycles and synchronization signals. The U18051 single-chip microcomputer has a built-in clock generator. When in use, you only need to connect a quartz crystal resonator (or other oscillator) and a capacitor to allow the system to generate a correct clock signal. "




In Figure 2, U2A is a high-precision, low-power voltage comparator LM393A, C6 is a battery, and BT1 is a solar panel. When sunlight shines on the solar panel BT1, the voltage across the solar cell BT1 increases, charging the battery C6, and capacitors C1 and C2 filter. D1 is a protective solar panel to prevent the solar panel from being reversely charged by the battery. Potentiometer R1 is used to adjust the LM393A The reverse terminal voltage adjusts the on/off time of the solar lawn light. When the solar panel BT1 is exposed to sunlight during the day, the voltage at both ends increases. Through the voltage divider R1, the voltage at the reverse terminal pin 2 of the LM393A chip is higher than the in-phase terminal pin 3. The LM393A outputs a low level from pin 1, which turns off the transistor Q1, and the 51 single-chip microcomputer U18051 is not powered on.
When the voltage at both ends of the solar panel BT1 decreases at night, through the voltage divider R1, the voltage at the reverse terminal pin 2 of the LM393A chip is lower than the in-phase terminal pin 3. The LM393A outputs a high level from pin 1, turns on the transistor Q1, and the 51 single-chip microcomputer is powered on and works.
The 51 MCU turns on the four colored LEDs in turn, and the cycle continues until daytime, when the 51 MCU stops working due to power failure.
The 51 MCU program is as follows:
   void main()
        {
          init()；//initialize
          while(1)；
          }
         void timer0() interrupt 1
         {
          TH0=(65536—50000)/256；
          TLO=(65536—50000)%256；
          a++；
         if(a=60)
              { a=0；
          b=_crol_(b，1)；
          if(b=0x10)
          b=0x01；
          P2=b；
            }
4 Conclusion
At present, the solar energy industry is still in its infancy, and there are still many problems to be solved. Problems such as low efficiency of solar panels and high price of solar panels restrict the development of the solar energy industry. However, as a new type of green energy, solar energy has broad application prospects in the field of lighting.