How Do the 12 Pins of a Four-Digit Display Work?
In the field of electronic displays, four-digit seven-segment displays are common components used in electronic devices. Each display consists of four seven-segment LED units, with each unit capable of showing a single digit (0–9) or specific characters. Thanks to their simple and clear numeric display functionality, four-digit displays have become essential components in instruments, clocks, and various control panels. This article explores their internal structure and working principles, with a focus on the proper assignment and usage of their 12 pins.
Catalog
I. What is a Four-Digit Display?
III. Principles for Allocating the 12 Pins
IV. Specific Allocation of the 12 Pins
V. Pin Allocation Considerations
I. What is a Four-Digit Display?
A four-digit display typically integrates four independent seven-segment LED displays into a single package. Each segment contains seven LEDs, usually labeled A, B, C, D, E, F, and G, which form different parts of a digit. In addition, there is a decimal point (DP) segment.
From the outside, a standard four-digit display usually has 12 pins. These pins are arranged on the bottom of the component. When the display face is oriented toward the observer, pin 1 is at the bottom left, and the numbering continues counterclockwise as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.
The core value of four-digit displays lies in their ability to provide clear numeric output at low cost and low power consumption, striking a balance between simple dot-matrix LCDs and complex OLED screens.
II. Working Principle
Four-digit displays usually operate using dynamic scanning. Since the four digits share the same segment pins (a, b, c, d, e, f, g, dp), each digit is quickly lit in turn via the digit select pins. Each LED segment connects to the external circuit through its pins, and applying the correct voltage level lights up or turns off the corresponding segment, thus forming numbers or characters.
III. Principles for Allocating the 12 Pins
The allocation of the 12 pins in a four-digit display follows clear principles:
· Common Anode vs. Common Cathode: The first consideration is whether the display is common anode or common cathode. In a common-anode display, the anodes (positive terminals) are tied together, and each segment’s cathode is separate. In a common-cathode display, the cathodes are tied together, and the segment anodes are separate.
· Segment Select and Digit Select: To display multiple digits, the pins are divided into segment select pins (which determine which segments light up) and digit select pins (which determine which digit is active).
· Number and Function of Pins: In a 12-pin four-digit display, there are usually 8 segment pins (A-G plus DP) and 4 digit select pins (to choose which digit is being displayed).
IV. Specific Allocation of the 12 Pins
· Segment pins: A, B, C, D, E, F, G correspond to the seven LED segments of the display and control which parts of the digit are lit. The DP pin controls the decimal point.
· Digit select pins: Usually, four pins (D1, D2, D3, D4) are used to select which digit is currently active. By controlling the voltage on these pins, each digit can be lit in sequence.
It's important to note that different display models may have different pin layouts. For example, the YH-E30461BMG-B5 is a 0.36-inch four-digit common-anode yellow-green LED display, while the 3461BS is a common-cathode display. Always refer to the specific datasheet for accurate pin functions and layout.
V. Pin Allocation Considerations
Proper allocation and usage of the display pins are crucial. Key points include:
· Pin Identification and Connection: Carefully check pin labels and ensure correct connection of segment and digit select pins. Wrong connections may cause display errors or damage.
· Current-Limiting Resistors: To protect LEDs from overcurrent, use resistors in series with segment pins. Resistor values should be calculated based on the LED voltage and current ratings and supply voltage.
· Driving Circuit: Choose the appropriate driving circuit according to the display type (common-anode or common-cathode) and display requirements. The circuit should provide enough current to light the segments reliably.
· Display Mode: Four-digit displays can operate in static or dynamic mode. Static mode lights all digits simultaneously, while dynamic mode rapidly switches digit select pins to light each digit in sequence, taking advantage of human persistence of vision to make all digits appear lit at the same time.
VI. Conclusion
Correct pin allocation is the foundation for proper operation of four-digit displays. Common-anode and common-cathode displays require opposite connection methods, and it is important to choose the right driving circuit and current-limiting resistors. Selecting the appropriate display mode (static or dynamic) and high-quality driver chips can optimize the display quality and reduce power consumption. Understanding the structure, principle, and pin allocation of four-digit displays ensures clear, stable output and improves the reliability and lifespan of the entire electronic system.
