1. Project introduction

The simple star-shaped breathing lamp is composed of LM358 op amp and peripheral circuitry, which consists of 20 LEDs arranged into a five-pointed star pattern.

2 Circuit Principle

2.1 Introduction to the chip

The LM358 consists of two independent operational amplifiers with high gain, high common-mode rejection ratio, and strong stability. It is suitable for use with a single power supply with a wide range of supply voltages, and is also suitable for dual supply operation. Wide range of use.

Fig.2-1 Footprint map of LM358 (SOP-8).

Table 2-1  Pin description of LM358

2.2 Typical Applications

LM358 and peripheral circuits form a triangular wave signal generator; The transistor forms a common collector circuit, which amplifies the triangular wave signal added to the base, and because the voltage of the base is a triangular wave sandwiched on the DC signal, the output voltage of the emitter is a triangular wave signal that moves upward, which can control the brightness of the LED lamp and form the effect of breathing.

Fig.2-2 Circuit diagram of a classic application of LM358

In Figure 2-2: The potentials of pins 3 and 6 of LM358 are fixed. When the 2-pin potential is lower than the 3-pin potential, the output of the 1-pin is high, that is, T1 is on, and the LED is on, 2The potential of the pin is provided by pin 7, and when the potential of pin 5 is higher than pin 6, pin 7 outputs high. The two op amps form an interconnected comparator to make T1 on and light up the LED.

3 Schematic design

3.1 New projects

Open the EDA Professional Edition, create a project and name it [Analog Circuit] LM358 Star Breathing Light, and name the schematic file SCH_LM358 Star Breathing Light. Draw a circuit schematic diagram based on the following circuits.

Fig.3-1 SCH_LM358 star-shaped breathing lamp

3.2 Device Selection

In the component selection of this project, all components can be directly in JLCEDA's component library. If you are not familiar with the components, you can also search by copying the item number in the material (each component has a unique item number in the LCSC).

Fig.3-2 Searching for a component

Fig.3-3 Searching by product number

3.3 Bill of Materials

4 Bezel design

Fig.4-1 Star frame design

In the top toolbar, modify the line 45° to the free angle of the line, place the line polyline (shortcut: Alt + L), press the Tab key to lock the entered value and switch the input length and angle, the side length of the five-pointed star is 36mm, the angle is shown in the above icon, Start at the top.

Fig.4-2-1 Star border 1 is drawn

Fig.4-2-2 Star border drawing 2

Fig.4-2-3 Drawing a star-shaped border 3

Fig.4-2-4 Star border drawing 4

Fig. 4-2-5 Drawing a star border5

Fig.4-2-6 Star frame 6 is drawn

Fig.4-2-7 Star border drawing 7

Fig.4-2-8 Star border 8 is drawn

Fig.4-2-9 Star border9 is drawn

Fig.4-2-10 Drawing a star-shaped border10

After finishing the five-pointed star drawing, select the entire five-pointed star, right-click the mouse, and add a 2mm circular chamfer to slow down the sharpness of the five-pointed star and make it smoother and safer.

Fig.4-3 Enter the value of the chamfer radius

Fig.4-4  Five-pointed star border design

5 PCB design

After completing the schematic design and checking that the circuit is connected to the network correctly after DRC, click "Design" → "Schematic to PCB" in the top menu bar(Alt+I) to save the PCB file to the same project and name: PCB_LM358 Star Breathing Light.

5.1 PCB Layout

During the device layout, the 20 LEDs are arranged and placed in the shape of a five-pointed star, and the rest of the devices are placed on the back, and TYPE-C is placed under the five-pointed star, as shown in Figure 5-1.

Fig.5-1 PCB layout reference diagram

5.2 PCB Traces

PCB ROUTING, THE FULL NAME IS PRINTED CIRCUIT BOARD LAYOUT (PCB LAYOUT). Because the circuit board has two sides, the top surface and the bottom surface, the PCB trace can also be divided into the top and bottom wiring, in which the top wiring is the red line by default, the bottom layer is the blue line, and other colors can also be set according to personal preferences.

Figure 5-2 shows the wiring reference, and the following figure can be used for the initial design.

Fig.5-2-1 Reference diagram of PCB traces - top layer

Fig.5-2-2 Bottom layer of PCB traces

5.3 Copper pouring and silk screen printing

After the PCB trace is drawn, the copper is poured, and the GND network can be connected. Silk screen characters follow the principle of left to right and top to bottom. Mark the project name and logo, and annotate the direction in which the switch is turned on.

Fig.5-3-1 Copper clad and silk screen printing of PCB - top layer

Fig.5-3-2 Copper clad and silk-screen printing of PCB - bottom layer

6 Circuit debugging

6.1 Device soldering

You can refer to the soldering sequence: first solder the LED on the top surface, and then solder the Type-C connector/toggle switch; secondly, the LM358 op amp chip was soldered; Re-soldering resistor/capacitor/tunable resistor; The circuits are all chip devices, and the soldering can be carried out according to the principle from low to high.

Fig.6-1-1 Top surface of the empty PCB

Fig.6-1-2 Bottom surface of the empty PCB

Pay attention to the soldering iron tip with electric safety hands during the soldering process to avoid burns. When soldering, the components are aligned to check whether the model is correct. During the soldering process, pay attention to whether the solder wire is soldered or missed, so as to avoid affecting the performance of the circuit and causing the circuit to not work normally.

Fig.6-2-1 Physical PCBA image - top surface

Fig.6-2-2 Physical PCBA diagram - bottom surface

Fig.6-3-1 Top surface of the 3D rendering

Fig.6-3-2 3D rendering - bottom surface

6.2 Hardware Debugging

After the welding is completed, you need to use a multimeter to check whether the power supply is short-circuited with the ground, whether there is a short circuit and open circuit during the welding process, and the power-on test can be carried out only after the inspection is correct.

After the TYPE-C is turned on, turn on the toggle switch, the board starts to work, the LED produces a breathing flicker effect, adjust the resistance of the adjustable resistor, and change the frequency of the breathing light flashing.

Fig.6-4 Working diagram of a simple star-shaped breathing lamp