Understanding Schematics: A Design Walkthrough

Every electronic design is based on a schematic diagram. The schematic diagram is the blueprint that shows how electronic components are connected to create a circuit. The schematics serve as a route map showing how current and signals will flow from the input stage to the output stage. Before a PCB (Printed Circuit Board) is actually made, we typically design a schematic. When it comes to the revision of the circuit, the main work is done first at the schematic level, and after that PCB is again modified as per specs. More than this, when it comes to circuit operation and debugging then circuit diagrams and schematic plays an important role.

In this article, we will examine a working schematic that combines: a power supply, input handling, a digital signal processor (DSP), an output stage, an LCD display, and control through a microcontroller. It is a fully tested and fabricated PCB that is available for educational purposes. Understanding each section of the schematic will also provide you with insight into how this schematic diagram provides direction for PCB design.

What is a Schematic Diagram?

A schematic is a symbolic representation of an electronic circuit. Instead of showing physical shapes or how the wires will be routed. The schematic uses symbols for components such as resistors, capacitors, ICs, and connectors. A schematic diagram is used in wire routing and printed circuit board (PCB) design. Lines denote electrical connections and are important for labelling signals, voltages, and ground references. In the PCB design process, the schematic stage (step one) defines the logic and function of the design onto the layout or routing.

Understanding Schematic Diagram:

The schematic diagram presents an audio signal processing system in which analog stereo inputs have been conditioned, processed through a DSP. Additionally, as a controller Arduino Nano is used. The values are reported on an LCD and output a stereo audio signal for amplification. To understand it fully, we can move through each section in order. Let us discuss the schematic sections one by one:

1. Power Section

The power section provides clean and stable supply voltages to all other blocks. In this, there is a DC jack which provides a stable +12V supply to the circuit. A diode for reverse protection, and because the current requirement is less, we are using the onboard voltage regulator of Arduino. And the whole assembly is ON/OFF with a slide switch.

2. Input Section

The input block with resistors( R1, R2) and capacitors (C10, C11) processes the incoming left and right audio channels (LIN, RIN). LIN and RIN are the net labels. These nets are connected to the digital signal processor on Pin 11 and Pin 15. The capacitors are used in the input to remove the DC offset, and the resistors are used to balance the signal level and impedance. This prepares the signal for clean processing in the DSP stage.

3. DSP( Digital Signal Processor)

The PT2313 IC is a 28-pin Digital Signal Processor used to handle tasks like volume, tone, and channel control.

• It communicates with the microcontroller via I2C lines (SCL, SDA).
• It takes audio input (LIN, RIN) and produces processed audio output (LOUT, ROUT).
• Capacitors (C8, C9, C2) handle filtering and stability.

This is the heart of the design and the component that digitally manipulates the sound.

4. Output section

Here, capacitors (C1, C3, C5, C8) pass the processed audio to external amplifiers or speakers. They block DC offsets and smooth the signal for clear sound reproduction. Proper trace routing during PCB layout minimizes noise coupling between channels.

5. MCU and control section

An Arduino Nano (U1) manages system control and communication. It interfaces with the DSP through I²C lines (SCL, SDA). It reads inputs from buttons or encoders and uses the pull-down resistors (R5, R6) for stable logic. This section ensures responsive and reliable user interaction.

6. LCD Section

The LCD shows system parameters, volume, and input source. It connects to the MCU via I²C, making wiring simple. The SCL and SDA are net labels used to connect one block with another without the need for physical wiring. During PCB design, LCD connectors should be placed near the board edge for visibility and accessibility.

How to Interpret a Schematic Diagram

A schematic analyzes how current and signals move through a circuit, from power to input, then processing, and finally output. Schematics may contain multiple circuit blocks, read from left to right or top to bottom. Circuits often have repetitive patterns.  Here’s a quick way to read it:

1. Power Section:
   Start here. Identify voltage sources (VCC, +12V) and ground (GND). Check diodes and capacitors for protection and filtering.
2. Input Section:
   Look for connectors labeled IN, LIN, or RIN. Resistors and capacitors here filter and prepare the signal for the next stage.
3. Processing Section (IC or MCU):
   This is the main logic or signal control block, such as a DSP or microcontroller. Follow the input lines going into the IC and note the communication lines, SDA and SCL.
4. Control Section:
   Includes buttons, encoders, or switches connected to the MCU for user control (e.g., volume or input change).
5. Output Section:
   The processed signal exits through capacitors to speakers or external connectors (labeled OUT, LOUT, ROUT).

Check Flow: Trace signals in this order: Power → Input → Processing → Output. Use net labels and reference names (R1, C3, U2) to follow connections.

Best Practices for Schematic Design

• Maintain a clear hierarchy by grouping related components into functional blocks.
• Always give nets names to the components to avoid confusion and for better understanding of the schematic design.
• Add decoupling capacitors close to every IC’s VCC pin.
• Ensure power and ground are consistent across the entire schematic.
• Use proper annotation and documentation of the component values, part numbers, and references to maintain design clarity.

From Schematic to PCB Design

After the schematic is developed and verified, it is transferred to a PCB layout. Here's how it’s used:

1. Netlist Generation: The schematic generates a netlist that relays all electrical connections..
2. Component Placement: Components are placed on the board according to logical flow..
3. Routing: Traces are drawn to actually connect the nets.
4. Validation: Electrical Rule Check (ERC) and Design Rule Check (DRC) verify.

A clean schematic will help with a fast and reliable workflow in PCB design and documentation.

Conclusion

A schematic is not just a picture; it is the intelligence behind or justification for your PCB. You can produce a better board once you understand the schematics and working principle thoroughly. It is not only about DSPs, because we are making a design walkthrough, which is why we took this example. There are a lot of things, like SI/PI analysis and high-speed considerations, that can be clarified with the help of schematics and components we are choosing. We do not have to design the whole circuit from our own; instead, there are datasheets and reference documents that come with each IC to solve the problem. But arranging all sections together in a unique, understandable form is a challenge. Here, we try to standardize the schematics from a designer's perspective. In the future, we will see some more design walkthroughs on PCBs and circuits.

Whether you’re creating your first schematic or optimizing a professional-grade DSP board, turning your ideas into high-quality hardware has never been easier.With JLCPCB’s one-stop PCB manufacturing and assembly service, you can easily transform your schematic into a finished, reliable circuit board ready for testing and deployment.