[Analog circuit] Simple heart-shaped running water lamp

1-Project introduction

      Simple heart-shaped running water lamp module, consisting of red, yellow and green LEDs, 18 in total. Arrange in a heart-shaped pattern.

2-Hardware introduction

2.1 Circuit principle analysis

Figure 1 System circuit diagram

       After the power is turned on, one triode will be turned on first due to the principle of the transiently stable multivibrator. Due to the influence of capacitor charging, the other triode will be turned on after a delay, and the previous triode will be turned off. This reciprocating cycle achieves the effect of LED lights flowing water. Let’s analyze it with an example:

Assuming that Q1 is turned on first, the group of LED1 will light up. Because Q1 is turned on, its collector ( C pole) voltage drops, causing the left end of capacitor C2 to drop, close to 0V . Since the voltage at both ends of the capacitor cannot change suddenly, the base of Q2 ( B pole) is also close to 0V , Q2 is cut off, so the group of LED2 connected to its collector ( C pole) goes out; at this time, the high voltage of Q2 collector ( C pole) ( LED2 and R5 are connected in series and then connected to C3 , although The LED is not lit, but the current path exists) The collector voltage of Q3 increases through capacitor C3 , Q3 will also turn on quickly, and the LED3 group lights up, so for a period of time, the collectors of Q1 and Q3 ( C electrode ) are both low level, the two groups of LED1 and LED3 are on, and the group of LED2 is off.

As the power supply charges C2 through resistor R2 , the base ( B pole) voltage of Q2 gradually increases. When it exceeds 0.7V , Q2 changes from the off state to the on state, the collector ( C pole) voltage drops, and LED2 This group lights up. At the same time, the voltage dropped by the collector ( C pole) of Q2 passes through C3 , causing the voltage of the base ( B pole) of Q3 to also decrease. Q3 changes from conduction to cutoff, and its collector ( C pole) ) voltage rises, LED3 group goes out.

Next, the circuit cycles according to the process described above. Three groups of 18 LEDs will light up in turn. Two groups will be lit at the same time. These LEDs are arranged crosswise into a heart-shaped pattern, and they will continuously flash and glow in a cycle. The effect of flowing display.

2.2 Border design

Figure 2 Heart-shaped border design

   The heart-shaped border consists of a rectangle (square) and two semicircles (central angle 180 °). Define the radius of the arc as R , then the board dimensions are: width 3.41R , height 3.12R .

The PCB size    of this design is: 83mm*73mm , where the power supply USB is placed in the right-angled area below and modified into a rectangular area.

   Description of the border drawing process: start drawing with the bottom corner of the pattern as the origin, set the canvas unit to mm , first select the layer as the border layer, select the wire in the PCB tool to draw, set the grid size on the right to 34.290mm , grid The size and ALT key grid are both set to 0.635mm , the line width defaults to 0.254mm , and the corners are selected to 45 ° (the color setting in the picture is for ease of display, and a white background is selected, which does not need to be modified for actual drawing), as shown in Figure 4 .

Figure 3 Actual frame size

Figure 4 canvas settings

   At this time, start from the origin, draw along the 45 -degree direction, and draw upward to the left until you reach the first grid point. The same goes for the slash on the right. As shown in Figure 5

Figure 5  Oblique line drawing

   After drawing the two diagonal lines, start looking for the center of the arc, and change the grid size to ÷ 2 , that is, to 17.145mm , as shown in Figure 6 . At this time, the center of the circle falls on the grid point, as shown in Figure 7 .

Figure 6  Modify the grid size

Figure 7  Arc center

   First draw the right arc and select the center arc tool.

Figure 8  Center Arc Tool

   First reach the center of the arc, click the left mouse button, and then reach the starting point on the right side of the arc (endpoint of the diagonal line), then move counterclockwise and stop at the Y- axis position (the arrival point is on the grid point). The same goes for drawing the arc on the left. Start drawing from the Y -axis arc endpoint to the left diagonal endpoint. The drawing process diagram is shown in Figure 9 .

Figure 9  Arc drawing process

   After the arc on the left is drawn, you will be prompted whether to merge the network (as shown in Figure 10 ). We are drawing a closed graph, so select OK here.

Figure 10  Merged network

2.3 Border detail design

2.3.1 Power supply port part

   The power supply port of this design is located directly below and uses TYPE-C 6pin for power supply. Because the existence of the power supply port will damage the bottom of the heart shape, this is inevitable. Before drawing the border, you can plan the location of the USB port first , so that the USB port is within the entire heart-shaped area.

   The drawing process of the power supply port is as follows: first modify the PCB grid size, grid size, and ALT key grid to 1.27mm . Then adjust the position of TYPE-C so that its center is on the Y- axis and the lower border line is just close to the frame. Then select the document layer and draw auxiliary lines. Based on the first grid line below the TYPE-C port, draw from the beveled border on the left to the right. This is used as the bottom edge of the board.

Figure 11  Drawing the bottom edge of the board

   After the drawing is completed, as shown in Figure 10 , then start drawing two rounded corners. Select the center arc tool to draw. The left and right circle centers are shown in Figure 12 . Draw an arc with a radius of 2 blocks.

Figure 12  Left and right arc centers

   The drawn document line is the border layer below. At this point delete the two slashes drawn previously

Figure 13  The drawn lower border

Figure 14  Delete the two slashes

   Switch the layer and element to the border layer and select the wire tool (the corner of the right wire should be set to 45 degrees) and connect the end points on both sides. Draw the diagonal border again (Figure 15 )

Figure 15  draws the diagonal border again

  Finally, select the previously drawn document layer (hold down the CTRL key for multiple selections) and change it to the border layer in the property bar on the right. At this point, the border part has been drawn.

Figure 16  Modify the underlying border properties

2.3.2 Drawing of hanging through holes

   Place a mechanical hole above the heart for easy hanging. Select the through-hole tool (first row, second from last) on the PCB toolbar, and then place it at a suitable position on the Y- axis (a certain distance from the upper border, the diameter of the via hole is sufficient).

Figure 17  Through hole tool

   After placement, select the through hole and modify the diameter of the hole to 3mm (this size is more commonly used, the size can be set according to your own situation)

Figure 18  Modify the diameter of the hole

   At this point, the drawing of the heart-shaped border is completed, and subsequent operations such as device placement can begin.

Figure 19  The border part is all completed

3 Debugging Precautions

3.1 Welding

      All devices in this design are direct plug-in devices. Soldering is easy, but you need to use diagonal pliers to cut off the excess pins. Welding precautions: Do not reverse the positive and negative poles of the LED. The position of the LED positive pole has been marked on the PCB. You need to insert the longer LED pin into the positive hole (the other LEDs that are directly inserted into the positive and negative poles will not be expanded here to judge). Better welding is when the LEDs are tightly attached to the PCB, which can make the LEDs more stable and prevent the pads from falling off due to instability. Pay special attention to the fact that the positive and negative poles of the left and right LEDs of the heart shape are symmetrical. Do not cause welding errors due to "inertia" during welding.

3.2 Power on

      Before turning on the power, check whether the TYPE-C socket is welded well. Because the PCB circuit board does not have a switch, theoretically there will be LED light after the power is turned on. In this design, there are 12 LEDs emitting light at any time. After observing for a period of time, if you find that an LED has not lit up, then the LED has an incorrect welding of the positive and negative poles, or the LED is damaged. It is recommended to check the circuit. If it is broken or the positive and negative poles are welded Error, please remove the LED and solder it again. The power supply reference voltage is 3-5V, using type-c power supply, the voltage is 5V. The greater the supply voltage, the brighter the LED, and the shorter the running water lamp cycle.

3.3 Waveform display

3.3.1 Waveform at the moment of power-on

Figure 20 Module power-on instant waveform

      Waveform analysis: The three inputs of the oscilloscope are connected to the bases of transistors Q1, Q2, and Q3 respectively. At the moment of power-on, the bases of the three transistors all reach a voltage of 0.7V, and the transistors are turned on. At time t1, the base voltage of transistor Q3 suddenly begins to drop and reaches 0V, and the corresponding LED goes out. Then it starts to gradually rise. When the base voltage of transistor Q3 rises to about 0.7V, the corresponding LED lights up. The base voltage of transistor Q1 drops rapidly, transistor Q1 is turned off, and the corresponding LED goes out. Then the voltage gradually increases. The cycle proceeds, one of the three triodes is in the off state, the LED of this group is off, the two triodes are in the conduction state, and the LEDs all light up.

3.3.2 Waveform at the moment of power outage

Figure 21 Waveform after the module is powered off

       The picture above shows three. The base voltage of the transistor changes. After the module stops supplying power, the LED goes out directly. After the module is powered off, the voltage drops (because the voltage of the capacitor cannot change suddenly).