What are the common causes and solutions for frequent flashing of LED light strips?

Work often need to use the LED light display circuit, such as how to design a blinking frequency of 2Hz LED light blinking circuit? Flashing frequency of 2Hz, that is to say, the LED flashing period of T = 1/f = 0.5s, that is, 500ms, that is to say, the requirement of the LED light 500ms flashes once, that is, the average second flashes twice. This requirement can be realized in many ways, the following recolux lists several commonly used examples for your reference and study.


1, the most classic MCU implementation if we have a processor (such as microcontroller, DSP, ARM, CPLD or FPGA, etc.), the realization of the LED lights at a frequency of 2Hz blinking will become very simple. We only need to use one I/O port of the processor to drive a transistor, which in turn controls the LED's on/off state. By writing a simple program, the programmer can make this I/O port output a high level every 250 milliseconds and then a low level for the next 250 milliseconds. Thus, the overall blinking period is 500 milliseconds, which is the blinking frequency of 2 Hz that we want. the output signal of the I/O port presents a specific waveform: it is actually a square wave signal with a frequency of 2 Hz.
The following is a common circuit design method to control the LEDs by using an NPN-type transistor to turn them on and off. In this circuit, when the I / O output high level, the base of the transistor receives a high level, it will conduct, so that the LED lights up; and when the I / O output low level, the base receives a low level, the transistor will cut off, and the LED lights go out.
2, the use of 555 timer is very common 555 timer, it is very powerful, it can generate a frequency of up to 300KHZ and adjustable duty cycle PWM wave. For its principle of operation as a square wave generator, the output waveform period is calculated by the following formula: TH (high level time) = ln2 × R1 × C1, and TL (low level time) = ln2 × R2 × C1, where the ln2 ≥ 0.7. To give the resistors R1 and R2 for 768KΩ, and capacitor C1 for 470μF as an example, we can calculate TH and TL are each about 250ms. TL are each about 250 ms. Therefore, the period T of the entire square wave is the sum of TH and TL, which is 500 ms, and the corresponding frequency is 1 divided by the period T, which is 2 Hz. We know that the output of the 555 timer has a driving capability of about 200 mA, so we only need to drive a single LED, and we don't need additional components such as a transistor to enhance its driving ability. You can directly connect the LED lamp to the output pin (4 pins) of the 555 timer, so as to realize the control of the LED lamp.


3, multi-harmonic oscillator This is a very classic LED alternating flashing circuit, which uses two NPN transistors and capacitor charging and discharging principle to realize the alternating flashing effect between LED1 and LED2. If you only need to control one or a group of LEDs, you can use a resistor instead of LED2.This circuit is a multi-harmonic oscillator circuit, where one of the transistors is in the on state, the other transistor will cut off, through the coupling of capacitors and resistors, these two transistors will alternate into the on and cut off state, thus generating self-excited oscillation. This oscillation mechanism makes the LED1 and LED2 can be realized between the smooth alternating flashing effect.

The working principle of this circuit is based on the charging and discharging process of the two NPN transistors and capacitors to realize. When the power on the moment, due to the small difference between the two sides of the circuit, so the two transistor conduction time will be first and later, resulting in one of the transistor first conduction, while the other is in the cut-off state, the formation of a temporary stable state. Take transistor Q1 on, transistor Q2 cutoff, for example, at this time the collector of Q1 (i.e., the left end of the capacitor C1) voltage is 0, while the base voltage of Q1 is about 0.7 V. At the same time, the capacitor C1 through the resistor R2 for charging, while the capacitor C2 also through the resistor R4 for charging. Assuming that the supply voltage VCC is 5V, when capacitor C2 is fully charged, the voltage at both ends of it is 4.3V (0.7V at the left end and 5V at the right end). Since the resistance value of R4 is much smaller than R2, the charging speed of capacitor C2 is much faster than C1. When the voltage at the right end of C1 reaches 0.7V, Q2 begins to conduct. At this time, the voltage at the right end of capacitor C2 is directly pulled down to 0V, but because the voltage at the two ends of the capacitor can not be changed abruptly, the voltage at the left end of capacitor C2 instantly becomes -4.3V, resulting in the immediate cutoff of Q1, forming another temporary stable state. Then, capacitor C2 began to discharge through the resistor R3, after discharging and then began to reverse charge. When the voltage at the left end of capacitor C2 reaches 0.7V, Q1 conducts again. Similarly, the conduction of Q1 will make the left end of capacitor C1 voltage becomes 0V, and then feedback to the right end of capacitor C2 voltage becomes -4.3V, so that Q2 cut off, and then enter the next temporary stable state. This process will be repeated, thus realizing the effect of LED1 and LED2 flashing alternately.

The oscillation period T of this polytuned oscillator can be calculated by the formula T=0.7(R2C1+R3C2). Since the values of resistors R2 and R3, capacitors C1 and C2 are the same, the period can be simplified to T=1.4×R2×C1. By adjusting the values of capacitors C1 and C2 as well as resistors R2 and R3, we can change the frequency of the LED's blinking. This circuit may be difficult for beginners to understand, but we can gradually master its working principle through practice.

Summary: This article introduces three commonly used LED blinking program.
The first program using the processor to achieve, although the realization of the process is relatively simple, but the premise is that the original system has a processor can be used, otherwise in order to a single LED blinking function and the design of a separate processor is uneconomical, high cost.
The second program uses 555 timer, is a commonly used method, only a 555 chip and some capacitive resistors can be realized LED blinking, its principle is simple and low cost.
The third scheme is based on the classic polyharmonic oscillator circuit, which requires only two transistors and a few capacitive resistors to realize LED blinking alternately, and has a lower cost.

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