PAGE 095 OF 150 · DISPLAYS & INDICATORS
Dot-Matrix LED Displays
A grid of LEDs can draw characters and shapes.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
One digit at a time
Multiplexing connects the same segment lines to every digit and switches on one digit at a time, repeating quickly so all of them appear lit.
Why it helps
Four digits normally need 28 connections. Multiplexed, they need only 7 segment lines plus 4 digit-select lines, which is 11 pins.
Details
- Switch each common pin with a transistor.
- Refresh the whole display at 50 Hz or more.
- Each digit is lit only 1 ÷ N of the time, so use a higher peak current within the LED's pulse rating.
- Blank all segments before changing digits to avoid ghosting.
REMEMBER
A seven-segment digit is seven small LEDs arranged to draw numbers.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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