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Mermaid
graph TB
    subgraph LED_Segments
        SEGA([SEGA]) --> "|Lt-Pos|"
        SEGB([SEGB]) --> "|Lt-Pos|"
        SEGC([SEGC]) --> "|Lt-Pos|"
        SEGD([SEGD]) --> "|Lt-Pos|"
        SEGE([SEGE]) --> "|Lt-Pos|"
        SEGF([SEGF]) --> "|Lt-Pos|"
        SEGG([SEGG]) --> "|Lt-Pos|"
        SEGDP([SEGDP]) --> "|Lt-Pos|"
    end

    subgraph Outputs
        outA([outA]) ==> SEGA
        outB([outB]) ==> SEGB
        outC([outC]) ==> SEGC
        outD([outD]) ==> SEGD
        outE([outE]) ==> SEGE
        outF([outF]) ==> SEGF
        outG([outG]) ==> SEGG
        outDP([outDP]) ==> SEGDP
    end

    classDef default fill:#ffccff,stroke:#333,stroke-width:2px;

    subgraph MAX7219EWG+$$MAX7219EWG+$$
        direction TB
        Outputs
    end

    style MAX7219EWG+ fill:#ffcccc,stroke:#333,stroke-width:2px;

• The LED segments are represented in the LED_Segments cluster.
• The outputs controlling each LED segment are in the Outputs cluster.
• Each output is connected to a corresponding segment.
• The MAX7219EWG+ is shown as the controller for the outputs.

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• Component: DC-DC Boost Converter
• Functionality: Boost 12V to 24V
• Connection: Connect the input of the boost converter to the 12V power source, and the output to the LED strips.

• Component: DC-DC Buck Converter
• Functionality: Step down 12V to 5V
• Connection: Connect the input of the buck converter to the 12V power source, and the output to supply power to the MAX7219.

• Current Rating: Ensure the converters can handle the current required by your load.
• Efficiency: Look for converters with high efficiency to reduce power loss.
• Heat Dissipation: Consider heat sinks if the regulators are expected to dissipate significant power.

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1. MOSFET Selection: Choose an N-channel MOSFET, which will allow you to control the connection from the digit cathode to ground.
2. Basic Connections:
   • Connect the source of the N-channel MOSFET to GND.
   • Connect the drain of the MOSFET to Digit0:Pin_1.
   • Connect dig0:P1 to the gate of the MOSFET.
3. Control:
   • When you apply a positive voltage to the gate (from a microcontroller like an Arduino), it will turn the MOSFET on, effectively connecting Digit0:Pin_1 to GND.
   • To turn off the digit, you can connect the gate to GND or to a low logic level to switch off the MOSFET.

• Connect MOSFET:Source to GND.
• Connect MOSFET:Drain to Digit0:Pin_1.
• Connect dig0:P1 to MOSFET:Gate.

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• The MAX7219 uses an internal multiplexer and digit drivers. Each digit pin (DIG_0 to DIG_7) is an open-drain output that sinks current when active.
• When the MAX7219 enables a digit, it effectively pulls the respective DIG_x pin to ground.

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1. Direct Connection: If you're only drawing 30mA per segment and not exceeding the total current rating for the entire display, you could, in theory, connect directly. However, keep these factors in mind:
   • Ensure that the total aggregate current doesn't exceed the maximum ratings for power dissipation or total current for the MAX7219.
   • Consider using a current-limiting resistor for each segment to help manage and distribute power.
2. Using a MOSFET: To reduce stress on the MAX7219, you might consider using N-channel MOSFETs for each digit line, especially since you're working with large LED segments that might approach MAX7219's limits. Here's how you could do that:
   • Gate: Connect the gate of each N-channel MOSFET to the corresponding digit output from the MAX7219 (DIG_0 to DIG_7).
   • Drain: Connect the drain of each MOSFET to the ground connection of your LED strip's segment.
   • Source: Connect the source to ground.
   This setup allows the MAX7219 to control the MOSFET gates, effectively switching the LED segment grounds on and off with lower current requirements from the MAX7219.

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1. 2N7000:
   • An N-channel MOSFET with a maximum drain current of around 200mA.
   • Suitable for low-power applications and easy to find.
2. BS170:
   • Similar to the 2N7000, with a maximum drain current of around 500mA.
   • Can handle more current and is suitable for higher-power demands.
3. IRLZ44N:
   • This is a logic-level MOSFET that can handle much higher currents, up to 47A.
   • It's overkill for your application but good for more high-current configurations.

• Logic-level compatibility, so the MOSFET turns on with a typical 5V logic signal.
• Drain-source voltage rating, which should exceed your supply voltage for safety.

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1. Basic Connections:
   • Collector: Connect the collector of the NPN BJT to the negative terminal of the LED segment.
   • Emitter: Connect the emitter to ground (GND).
   • Base: Connect the base to the MAX7219's digit output (DIG_n) through a current-limiting resistor.
2. Current-Limiting Resistor:
   • The resistor between the MAX7219's output and the base of the BJT is necessary to limit the base current and protect the MAX7219. A typical value might be around 1kΩ, but you can adjust this depending on the specific characteristics of your BJT.
3. BJT Selection:
   • Any general-purpose NPN transistor should work, provided it can handle the current requirements. Some popular choices include:
     • 2N3904
     • BC547

• Connect BJT:Collector to the negative terminal of the LED segment.
• Connect BJT:Emitter to GND.
• Connect BJT:Base to MAX7219’s DIG output through a resistor (e.g., 1kΩ).

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1. Purpose of Digit Pins:
   • The digit (DIG_x) pins on the MAX7219 are intended to directly control the ground side of the connected segments, sinking current when the digit is active.
2. Use with BJTs:
   • If you're using an NPN BJT to drive the segments, you'll have a base resistor between the MAX7219 output and the BJT's base. This configuration controls the current and protects the MAX7219. No additional pull-up resistor is needed here.
3. Potential Issues with Pull-Up Resistors:
   • Adding a pull-up resistor could interfere with the intended operation by causing unwanted current paths, leading to unexpected behavior or even overloading the MAX7219 when digit pins are pulled low.

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1. Number of Digits:
   • If you are driving more than 8 digits, you will need more than one ULN2803A, as each digit will require a separate channel.
2. Current Handling:
   • Each channel can handle up to 500mA, which is more than enough for a typical 7-segment LED digit (30mA per segment * 8 segments = 240mA total per digit).
   • Ensure the total current handled by the ULN2803A does not exceed its maximum rating of 2.5A across the entire chip.
3. Project Needs:
   • For a typical setup with multiple digits (up to 8), one ULN2803A should suffice to drive these unless you are exceeding the current or channel limits.
   • If your project requires more than 8 digit control lines, simply use additional ULN2803A ICs as needed.

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1. Using BJTs or MOSFETs for Digits:
   • This is a common approach for controlling digits, especially since the digit lines are managing the ground connection (sinking current).
   • As previously discussed, you can use N-channel MOSFETs or NPN BJTs to switch each digit on or off by connecting the MOSFET/BJT's drain/collector to the digit pin and the source/emitter to ground.
2. Using ULN2803A for Digits:
   • This is also a viable solution if you prefer a unified approach or want to simplify your design using only one type of component.
   • The ULN2803A can sink enough current for typical digit operations, and it can support multiple digits if needed.

• Design Complexity: If you have the transistors available, using them might reduce design complexity by separating segment and digit control.
• Power Distribution: Ensure that the total current through each ULN2803A does not exceed its ratings. Distributing operations between ULN2803A and transistors can help balance loads.
• Component Availability: Choose an approach that aligns with the components you have available and your overall design strategy.

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1. Digit Control:
   • Each digit pin (DIG_0 to DIG_7) on the 7-segment display connects to a channel (output) on the second ULN2803A.
   • Connect each ULN2803A output pin (e.g., OUT_1 to OUT_8) to the corresponding digit (anode) of your display.
2. Inputs from Controller/Driver:
   • Connect the respective control signals from your microcontroller or driver IC (e.g., the MAX7219) to the inputs (IN_1 to IN_8) on the ULN2803A.
   • These signals will turn each digit on or off by pulling them to ground when activated, in effect controlling which digit is displayed.
3. Common Connections:
   • COM: Connect the COM pin of the ULN2803A to a higher potential (like +5V) if you're using free-wheeling diodes inside the ULN2803A. This is usually more relevant for inductive loads, but not strictly necessary here.
   • GND: Ensure the GND of the ULN2803A is connected to your system ground to complete the circuit.

• Control Signals: The control signals from the microcontroller should switch between high and low logic levels, where 'low' activates the ULN2803A output (digit on), and 'high' deactivates it (digit off).
• Consider Segment Current: Ensure each digit connection's sink current can be safely handled by the ULN2803A and that it matches the required drive for your LED strips.

• Connect ULN2803A outputs (e.g., OUT_1 to OUT_8) to digit anodes.
• Connect ULN2803A inputs (IN_1 to IN_8) to microcontroller outputs or a driver IC like the MAX7219.
• Connect the GND of the ULN2803A to your system ground.

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1. MAX7219 Digit Logic:
   • The MAX7219 digit pins are open-drain outputs designed to sink current. When a digit is selected, it pulls the corresponding DIG_n line to ground.
2. ULN2803A Operation:
   • The ULN2803A is also designed to sink current, but it won't be directly useful for interfacing with the MAX7219's digit outputs because both are meant for sinking.

1. Use MOSFETs/BJTs for Digit Control:
   • Continue using MOSFETs or BJTs as previously discussed to control the digit lines. The MAX7219's open-drain outputs can drive the base of a BJT or the gate of a MOSFET directly, effectively grounding the digit line when desired.
2. Interfacing Logic for ULN2803A:
   • If you still wish to use the ULN2803A, you would need additional logic to convert the MAX7219's sinking operation to a sourcing operation for the digit lines, such as using a PNP transistor or P-channel MOSFET paired with the ULN2803A.
3. Common Cathode Control:
   • If you are utilizing common cathode configurations, ensure that your digit control can effectively provide the necessary sourcing current with an appropriate logic level.

• Use the MAX7219 to directly drive the digit transistor bases or gates (NPN/BJTs or N-channel MOSFETs). This respects the open-drain nature and simplifies the circuit.

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1. TD62783APG/TD62783AFG:
   • This is a PNP Darlington transistor array, typically used for sourcing current.
   • It offers up to 8 channels and can provide the necessary sourcing current for driving digit lines.
2. ULN2003A paired with PNP transistors:
   • While the ULN2003A itself is another sinking array with 7 channels, you can pair it with external PNP transistors for sourcing.
   • This modular approach offers flexibility, covering up to 7 channels with each IC.

• Connect the outputs to the positive side of the digit you wish to control.
• The array will source current when activated by a low signal on the input, suitable for interfacing with digit lines directly.

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1. Another ULN2803A:
   • You can use an additional ULN2803A for digit control. It provides 8 channels capable of sinking current, which suits your need to pull the digit lines to ground.
2. ULN2003A:
   • This array provides 7 channels. It can be used similarly to the ULN2803A, though it has one less channel.
3. ULN2064B:
   • This option supports higher currents per channel (up to 1.5A), but it has 4 channels, so you'd need two to cover 8 digits.

• Inputs: Connect the control lines from your microcontroller or driver (like MAX7219) to the respective input pins of the NPN array.
• Outputs: Connect the outputs of the array (e.g., OUT_1 to OUT_8) directly to the corresponding digit grounds.
• Common Ground: Ensure the ground of the ULN2803A is connected to the common ground of your circuit.

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1. Control the ULN2803A via a Current-Sinking Path:
   • Use an inverter to convert the MAX7219's sinking output into a sourcing signal, which can control the ULN2803A.
2. Component Setup:
   • Use an N-channel MOSFET or NPN transistor to interface each digit line:
     • Connect the gate/base to the output of the MAX7219.
     • The source/emitter connects to ground.
     • The drain/collector connects to the respective input channel of the ULN2803A.
3. ULN2803A:
   • The ULN2803A output pins will connect to the negative side of each digit line.
   • Ensure each digit line is correctly wired through the ULN2803A so that when the MOSFET/Transistor turns on, it enables a ground path for the respective digit via the ULN2803A.
4. Power Rails:
   • Connect the common pin (COM) of the ULN2803A to the appropriate positive supply voltage if using internal diodes (not strictly necessary if not managing inductive loads).

• Attach each MAX7219 digit output to a MOSFET/Transistor gate/base.
• Collectors/drains connect to ULN2803A inputs.
• Outputs of ULN2803A then go to the digit grounds.

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1. Component Selection:
   • Consider using a PNP Darlington array like the TD62783APG, which can provide sourcing current to each digit when enabled.
2. Basic Setup:
   • Outputs: Connect the outputs of the PNP array to the digit lines of your display.
   • Base Control: Each input on the PNP array connects to a microcontroller or inversion logic that will pull it low to turn the digit on, thereby allowing current to flow to the digit.
3. Power Supply:
   • Connect the common terminal of the PNP array to ground (if available), or ensure it's configured per the array's specifications.

• Digital Control: Your controlling logic will need to drive the input of the PNP array low to switch it on (source power to the digit).
• Resistors: Incorporate current-limiting resistors at the base inputs to control the base current. Typical values might range from 1kΩ to 10kΩ depending on the specific PNP array.

• When a digit needs to be illuminated:
  • Pull the respective input of the PNP array low.
  • This causes the array to source current to the digit line, turning that digit on.

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• Collector-Emitter Voltage (Vceo): Maximum 45 V
• Collector Current (Ic): Maximum 800 mA
• Power Dissipation (Pd): 625 mW

1. Load Current: Make sure that the load current does not exceed 800 mA. Given the typical nature of display driving, if this applies here, the current should be considerably lower.
2. Voltage Levels: Ensure that the voltage across the collector-emitter does not exceed 45 V during operation.
3. Power Dissipation: Calculate the anticipated power dissipation to assure it’s within the 625 mW maximum rating.

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1. Base Connection: The base of the Q1 transistor is connected to the U1 pin of the MAX7219. This means the MAX7219 will drive the base of the transistor to control the digit.
2. Emitter Connection: The emitter of the Q1 is connected to +12V. In a PNP transistor configuration, this is correct because you want the emitter at a higher potential to allow current to flow from emitter to collector when the base is pulled low.
3. Collector Connection: The collector is connected to the out0 signal, which is linked to the positive end of the LED strip. This configuration is proper for controlling the power to the LED strips, as the MAX7219 will make a current path through the transistor.
4. ULN2803A Connection: The negative ends of the LED strips are connected to the ULN2803A, which acts as a low-side switch driven by the segments outputs (segA to segG).

• The LED strips draw a current within the transistor's current rating $800 , \text{mA}$.
• The forward voltage of the LEDs sums to a total that leaves room for the required voltage drop across the transistor to stay within its ratings.

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• Off State: When the voltage at the base is close to the voltage at the emitter (in this case, +12V), the transistor remains off, and no current flows from emitter to collector.
• On State: To turn the BC327 on, you need to make the base voltage lower than the emitter voltage. This is typically achieved by grounding the base or by making it sufficiently low relative to the emitter voltage (+12V in this context). When the base voltage is lower than the emitter by at least around $0.6V$ to $0.7V$, the transistor begins to conduct, allowing current to flow from emitter to collector.

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1. Base-Emitter Voltage Difference: For the BC327 to turn on, the voltage at the emitter (+12V) needs to be higher than the voltage at the base. In an ideal situation, a PNP transistor turns on when the base is at least about 0.6V to 0.7V lower than the emitter.
2. Logic Levels: If the DIG_0 of the MAX7219 is at 5V when active, then the voltage difference between the emitter (+12V) and base (5V) is 7V. This is sufficient to turn on the transistor because it exceeds the required 0.6V to 0.7V.
3. Turning Off the Transistor: When the DIG_0 line is high (at 5V), the base-emitter junction is still forward-biased because +12V is applied to the emitter, which means the BC327 will conduct. If the DIG_0 line goes low (0V), the transistor will turn on even more strongly, allowing more current to flow through.

• To Turn On the BC327 (for DIG_0 active): DIG_0 should be 0V.
• To Turn Off the BC327: DIG_0 should ideally be pulled up closer to 12V or at least left at 5V.

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1. Base Resistor ($R_B$): Place a resistor between the DIG_0 output of the MAX7219 and the base of the BC327. This helps limit the current into the base when the transistor is on.
2. Pull-up Resistor ($R_P$): Add a pull-up resistor between the base and the +12V supply. This resistor helps to ensure that when DIG_0 is at 5V, the base voltage is closer to the emitter voltage, turning the transistor off.

• Base Resistor ($R_B$): You can start with a value like 10kΩ. This value limits the base current, which is adequate for switching. The value can be adjusted depending on the required base current and switching speed.
• Pull-up Resistor ($R_P$): A higher value like 100kΩ can be used. The pull-up resistor should have a value high enough not to interfere significantly with normal operation (so the transistor can still turn on), but low enough to pull the base towards 12V when DIG_0 is at 5V.

• Transistor On: When DIG_0 is 0V, the base-emitter junction is sufficiently forward-biased. $R_B$ limits the base current.
• Transistor Off: When DIG_0 is 5V, the pull-up resistor $R_P$ helps to lift the base voltage closer to the emitter voltage, minimizing the base-emitter voltage and turning the transistor off more effectively.

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• Base Resistor ($R_B = 1kΩ$):
  • Limits the base current when the transistor is on.
  • Ensures the base-emitter junction does not draw excessive current when conducting.
• Pull-up Resistor ($R_P = 100kΩ$):
  • Connected between the base and emitter (+12V).
  • Pulls the base voltage up toward +12V when DIG_0 is high (5V).
  • Helps ensure the PNP transistor is turned off more effectively.

• Transistor On (Base Pulled Low):
  • DIG_0 at 0V results in sufficient voltage drop across the base-emitter junction, turning the transistor on.
  • Base current is limited by 1kΩ, which helps protect the MAX7219 and the transistor.
• Transistor Off (Base at 5V):
  • With DIG_0 at 5V, the pull-up resistor helps bring the base voltage closer to the emitter voltage.
  • This configuration reduces the base-emitter voltage, turning the transistor off or at least minimizing its conduction significantly.

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• Serial Clock Frequency (f_CLK): The MAX7219 can support SPI clock frequencies up to 10 MHz. This high frequency allows for fast data updates to the display.
• Data Propagation Delay: The delay from the rising edge of the serial clock to the data update is typically very small, in the nanosecond range, allowing for rapid updates between each digital output.

• Display Refresh Rate: The MAX7219 continuously refreshes the LED display at a rate sufficient to ensure no visual flickering under typical conditions, usually refresh rates are controlled through the on-chip oscillator.
• SPI Command Execution: Commands such as digit updates happen almost instantaneously beyond the communication delay, allowing for responsive changes to the display.

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1. Arduino Nano Shield: You're using a template that includes an official pinout for the Arduino Nano, which is great for ensuring compatibility with other components.
2. MAX7219EWG+: This IC is used to drive LED displays, and it seems to be connected with various segment and digit nets like SEG_A, SEG_B, etc., and DIG_0, DIG_1, etc.
3. ULN2803A: This is a Darlington transistor array, often used to drive high-current loads like relays or LED segments. It's connected to the segment nets, which is appropriate.
4. NRF24L01 Breakout Board: This is a wireless communication module. It's connected to SPI nets (MOSI, MISO, SCK) and control nets (CE, CSN) with an appropriate power supply.
5. Power Supplies: Your project has power nets labeled +5V, +12V, and +3V3. Make sure that all components are receiving the appropriate power levels.
6. Connections:
   • SPI-related signals are appropriately connected between the NRF24L01 and the Arduino.
   • The MAX7219 is connected to the necessary segments and digits, which should control the LED segments.
   • Appropriate power connections and grounding are made.

• Check for Power Levels: Confirm that all components are receiving correct voltage levels.
• Load and Test Firmware: Make sure your Arduino Nano sketch is correctly set up to interface with each device.
• Testing: Before finalizing the PCB, test the setup on a breadboard to ensure all components are operating as expected.

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• +12V Power Supply: If you're driving loads that operate around this voltage.

• Connect $\text{U5:COMMON\_FREE\_WHEELING\_DIODES}$ to +12V.

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1. MAX7219 Configuration: The MAX7219 receives data from a microcontroller and lights up the required segments based on the input data.
2. Segment Control:
   • Segments controlled by MAX7219 need to be connected to the appropriate segment pins (SEG_A through SEG_G).
   • Digits are controlled by the corresponding digit pins (DIG_0, DIG_1, ..., DIG_7).
3. Connections for Displaying "8":
   • Ensure the data sent to the MAX7219 for DIG0 corresponds to lighting up all segments.
   • If you're manually controlling the segments, set the following:
     • Connect U1:$14 / SEG_A$ to ON
     • Connect U1:$16 / SEG_B$ to ON
     • Connect U1:$20 / SEG_C$ to ON
     • Connect U1:$23 / SEG_D$ to ON
     • Connect U1:$21 / SEG_E$ to ON
     • Connect U1:$15 / SEG_F$ to ON
     • Connect U1:$17 / SEG_G$ to ON
   • Connect U1:$2 / DIG_0$ to the common cathode or anode depending on your display type.
4. Microcontroller Code: Ensure that your Arduino sends the correct command to the MAX7219 to enable all the respective segments for DIG0.

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• ULN2803A (U2): This is a Darlington transistor array that can drive high currents. When used to drive a 7-segment display, its outputs (like OUT_1, OUT_2, ..., OUT_7) are typically connected to the individual segments (A to G) of the display.
• Segment Activation:
  • When a segment is "selected" or activated at U2, the corresponding output pin will be pulled low (connected to ground), allowing current to flow through the segment.
• Digit Selection (U5):
  • The outputs of U5 (such as OUT_0, OUT_1, ..., OUT_7) are used to drive the common cathode/anode of the 7-segment display digits.
  • If a particular digit (e.g., DIG0) is active, it should be connected so that it completes the circuit for the activated segments.

• If U2 is active: This means that when a segment is selected by U2, the corresponding segment is pulled to ground, enabling current flow through that segment.
• For U5 driving the digit:
  • DIG0 driven to GND: This will allow the selected segments to light up for DIG0 if it's a common cathode display.
  • OUT0 is off and OUT1 to OUT7 are on: This would typically mean that the other digits are inactive, and only DIG0 is active, which is what you want if you want to display something on DIG0 only.

• Segment Control: Current through activated segments is flowing correctly to light them up.
• Digit Control: The correct digit (DIG0) is being driven low to complete the circuit for the segments.