PWM - Control the brightness of LED with buttons

I wrote a blog post about PWM a year ago, the link is as follows:

http://hi.baidu.com/do_sermon/item/ff523b0a8b9d3d173b53ee74

An oscilloscope is used in this paper to display waveforms with different duty cycles.

In fact, LED can also be used to show the changes in PWM parameters through brightness. The actual test shows a very good effect. However, when using PROTEUS for simulation experiments, we can only see severe flickering and basically no change in brightness.

Recently, it has been discovered that adding a large capacitor can reduce the flicker of the LED and make the brightness more stable. In this way, the brightness changes can be directly observed using PROTEUS software.

The circuit is shown in the figure below. The capacity of the large capacitor (C6) in the figure is 4700uF, which can be adjusted at will, and the actual circuit does not need it.

The duty cycle parameter in the figure is 10, and the LED (D1) is displayed in the "half-bright" state.

The C program was published last year, and can be found in the link above. It has been slightly modified as follows:

#include

unsigned char a, b;

sbit K1 = P3^2; //Define two keys to adjust the duty cycle

sbit K2 = P3^3;

//------------------------------------------------

void delay(unsigned int i)

{

    unsigned char j;

    while(i--) for(j = 0; j < 60; j++); 

}

//------------------------------------------------

void main()

{

    TMOD = 0x01; //T0 timing mode 1

    TH0 = (65536 - 500) / 256; //500us@12MHz

    TL0 = (65536 - 500) % 256;

    TR0 = 1;

    ET0 = 1;

    EA = 1;

    a = 0;

    b = 10;

    while(1) {

      if(!K1) {delay(20); if(!K1) {b++; if(b > 19) b = 19; while(!K1);}}

      if(!K2) {delay(20); if(!K2) {b--; if(b < 1) b = 1; while(!K2);}}

      //The above two lines are to check the key, delay debounce, modify the duty cycle, and wait for the key to be released, b = 1~19

      P0 = ((b / 10) << 4) + b % 10; //Display duty cycle level

    }

}

//------------------------------------------------

void time0() interrupt 1

{

    TL0 = (65536 - 493) % 256; //Compensation interrupt entry time

    TH0 = (65536 - 493) / 256; //500us@12MHz

    a--; //a = 1~20

    if(a == 0) {a = 20; P2 = 0;} //Period = 20*500us

    if(a <= b) P2 = 255; //output to oscilloscope

    P1 = ~P2; //Output to LED, low level light

}

//------------------------------------------------

In this program, the PWM cycle is shorter than last year's. Last year, it was designed to be 1s in response to the requests of netizens, which was a bit long and not very practical.

This time, we don't need external interrupts to input keystrokes, but use the key query method instead.

When the duty cycle is adjusted using the buttons, the LED can display different brightness. Several screenshots are as follows:

When the PWM parameters are slightly smaller, the brightness is somewhat insufficient, which can be compensated by appropriately reducing the resistance of some current limiting resistors.

The LED used to display PWM has intermittent current, so its current limiting resistor can be smaller than usual, around 100 ohms, which is an empirical data.

When making a physical circuit, you don't need a large capacitor, so you don't have to spend money to buy it, haha