Guitar water lamp

1 Introduction

The LED running water lamp made of NE555 and CMOS decimal counter can achieve the effect of running water lamp after being powered through the USB interface.

2. Schematic diagram

2.1 Power supply

The power input interface uses Type-C. Because it is a pure circuit implementation, only +5V and GND are connected for power supply.

2.2 NE555 and potentiometer

First, let’s take a look at the internal structure of the NE555. There are three resistors with equal resistance between VCC and GND. Pins 2 and 6 are connected to a comparator respectively. The two comparators are connected to an RS flip-flop. The left end of the RS flip-flop is R When the pin and S pin receive different digital signals, different signals will be output from the right end. See the table in the figure for specific information. Pin 4 is the reset pin and needs to be connected to high level when used.

Here I connected a capacitor to pin 5 of NE555, and pins 2 and 6 were connected to the right end of the potentiometer. When adjusting the resistance of the potentiometer, the voltages of pins 2 and 6 will also change accordingly. When the voltage of pin 6 is greater than pin 5, the first comparator outputs high level, and the second comparator outputs low level. At this time, the Q pin of the RS flip-flop outputs low level, Q outputs high level, and the transistor is turned on. , the + terminal voltage of the second comparator becomes greater than the voltage of pin 2, and the output is high level; at the same time, the voltage of the - terminal of the first comparator is greater than the + terminal voltage, and the output is low level. At this time, the Q terminal of the RS flip-flop outputs high level. level, thereby outputting a square wave at pin 3.

The main function of the potentiometer is to change the voltage of pins 2 and 6 of the NE555, thereby changing the square wave frequency output by the NE555 and achieving a "variable speed" effect of the running water lamp.

2.3 CMOS decimal counter

CD4017 has 10 decoding output terminals (Q0~Q9), and CLOCK, RESET, and INHIBIT are input terminals. When INHIBIT is low, the counter counts on the rising edge of the clock; otherwise, the counting function is invalid. When RESET is high, the counter is cleared. Therefore, these two pins should be connected to low level. The square wave signal with a certain frequency output from the NE555 enters the CD4017 from the CLOCK pin. The Q0~Q9 terminals of CD4017 will output high levels in sequence with the input of the square wave signal at the CLOCK terminal. The Q0~Q9 terminals are connected to the LED lights. , realizing the effect of running water lamps

2.4 Running water lamp

In fact, there is nothing to explain when it comes to the running water lamp. Because the board is relatively small, in order to compress the space, a resistor is used, and the remaining two LEDs are connected to resistors. It should be noted that the methods of using resistors and resistors are different. Don’t make mistakes when drawing the schematic diagram. When I drew this schematic diagram before, I made a mistake in connecting the resistors, but I corrected it in time.

3. PCB, 3D preview and actual picture

4. Problems encountered

When I first drew the schematic diagram, when drawing the resistors and resistors on the LED, I mistakenly thought that the principles of resistors and resistors were similar. There was a problem at the beginning, but it was quickly corrected in the end. Overall, I did not encounter any major problems in drawing the schematic and PCB.

During the welding process, because it was the first time to weld a circuit board, I was a little unskilled. When welding LEDs, one of the LED lights added a little less solder, which caused all the LED lights to be soldered when the welding was completed. It worked normally, but after a period of time when the power was turned on again, one of the LEDs failed to light up. After re-soldering the LED that did not light up, the problem was solved.

Finally, let me talk about my feelings in this science and technology innovation club activity. In fact, this activity is quite interesting. The final product is quite beautiful. I feel that my efforts in the past few days are worth it. When I started drawing the schematic diagram, I didn't know much about the principle. When I was drawing the schematic diagram, others led me to complete it bit by bit. However, later on, I understood the working principle through the gradual learning process, and finally completed it. work.