Schematic wiring, Part 1

In the previous chapter we added the circuit components to the canvas. In this chapter, we will start work on the wiring. We’ll make full use of the techniques we learned in the previous two projects, and especially buses and labels.

Let’s begin with the connector. Consult the breadboard wiring diagram to find out the role of each pin. We will assign pin #1 to be connected to five volts, pin #2 will be connected to ground, pin #3 will be latch, pin #4 will be clock, and pin #5 will be data. So, let’s put in a VCC component. So that will go say here, and I put in a ground component as well GND. So that will go rotated, that’ll go here. And I can do the wiring, so W. Just start the wiring, and it will go around here to pin number one. Same thing for ground, click to start the wire and that would be connected to number two. This is very similar to how we configured the connector in project two, so I will show you the way the connector will look like on the schematic now:

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The wiring of the connector.

In the connector schematic, notice the GND, VCC and PWR_FLAG components, all added via the component chooser. We use labels for pins 3, 4 and 5, though which we will achieve connection with other parts of the circuit.

To make the connector part of the schematic easier to identify, I would also like to wrap it in a box, and give it a name. First, select the line tool from the right vertical toolbox:

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With the line tool you can draw boxes and other shapes.

Draw a box around the connector schematic:

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With a box outline, we can mark out parts of the schematic.

Add a name to this part of the schematic. Use the Text tool:

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With the Text tool you can add arbitrary text to the schematic.

Click inside the box you just created, somewhere in the top right of the box. The Text properties window will come up. Type something like “Connector to the Arduino” in the text box:

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Type some text in the text box, and click OK.

The text label you just created is now tethered to the mouse pointer. Place it in the box, so that at the end you have something like this:

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This part of the schematic is now marked and titled.

The box and the title we just added are not part of the circuit! They only serve in marking out special parts of the circuit. They just make the schematic easier to read.

Do the exact same thing for the capacitor. Add the VCC and GND components, place the area in a box, and give it a title. It should look like this:

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The capacitor part of the schematic, boxed and titled.

Next, let’s switch our attention to the resistors and LEDs. Because of the way we positioned these components in the previous chapter, one next to the other in two columns, we can simply use wires to connect them. Type “W” to select the wire tool, or click on the Wire tool button from the right tool bar, and draw the wires.

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Use normal wires to connect the LEDs to the resistors.

The circuit requires that the anode of each LED is connected to VCC. The cathodes will be connected to the shift register data pins. So, lets add the VCC component next, and connect the resistors to it, for both LED banks. The first LED bank circuit will look like this:

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Added a VCC component, and completed the connections with the LED anode, via the resistors.

Notice the solid green dots indicating that the wires actually connect instead of only intersecting. The two LED banks, completed, look like this:

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Both LED banks connected to the VCC component via the current limiting resistors.

We’ll continue with the data pins and wires. Because we have 8 data pins for each LED bank, it is preferable to bundle them together via buses. We will create one bus for each LED bank, and assign 8 data signals to each bus.

Start the process for the first bank by labelling the data pins on the shift register and the LEDs, then draw the bus, add the bus entries, and finish with the wiring between the bus entries and the pins.

Click on the Local Label button:

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Select the Local Label button.

Next, add labels to pins QA to QH of the shift register, and the 8 LEDs that are across it. The labels that you create should contain the same name for each data pin and LED pair. The schematic should look like this:

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The data pins and LEDs are now labeled.

Notice how a label is structured according to a convention: “led_x_y”, where “x” is the number of the LED bank (in this example, we are working on bank 2 of 2), and “y” is the number of the data pin (1 of 8, 2 of 8 etc). Also notice that the same label is used for pins that are meant to be electrically connected. So, the shift register pin QA is meant to be connected to the LED at the top of the bank. The names of the labels will be used to name the corresponding net. Later in Cvpcb, we will see these nets again, so it is important to choose names that have meaning otherwise there is a good change you will get confused later!

Let’s create the bus next. Select the bus too from the right tool bar:

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The bus tool button.

Draw a bus as a single line between the shift register IC and the LEDs:

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The blue line represents a bus.

Select the bus entry tool from the right tool bar:

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The bus entry tool.

And create entries on the IC side first:

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Added bus entries. They are very similar-looking to normal wires, except that they are at a 45 degree angle.

Use a normal wire (“W” key) to connect each pin of the shift register with a bus entry:

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The pins are now connected with a corresponding bus entry.

Repeat the process on the LED side: add bus entries and connect them to the LEDs:

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The LEDs are now connected to the bus.

The shift register is now fully connected to the LEDs. Draw a boundary around this part of the schematic, and give it a name, like “LED Bank 2”:

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This part of the schematic highlighted and titled.

Repeat the exact same process for the other shift register IC and its LEDs. To avoid boring you, I will just show you the end result:

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This is the LED Bank 1 segment of the schematic, complete with a bus, bus entries, net labels and wires.

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Detail, showing a text label with the name of this segment for the schematic.

We have made substantial progress so far: the shift registers and the LED as connected via buses, and the connections to the capacitor and the connector are complete.

Next, we need to complete the circuit by connecting the shift register communications pins to the connector. We will use net labels for this. Let’s proceed to the next chapter and to get this done.

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