Customer:
I bought a 3x LED 7-segment white display with common cathode and can’t find documentation on how to use it. I managed to light up a couple of segments using a multimeter’s diode testing but can’t figure out how to make it actually work and display numbers. I need documentation or guidance on how to control it.
Originally submitted via email support on 9 October 2025. Migrated to the forum for community visibility.
Soldered Support:
Your module is a 3-digit common-cathode 7-segment LED display. Each digit shares a cathode (negative) pin, and all digits share the same segment pins (a–g and DP). To display numbers, the Arduino switches between digits very quickly (multiplexing), lighting one at a time fast enough that all appear on together.
You can follow this guide for the basics of single-digit wiring:
For three digits, use the SevSeg library — it handles the multiplexing automatically.
Wiring Segments (a–g, DP): connect each through a 220–470 Ω resistor to Arduino pins (shared by all digits). Digit cathodes: three pins, one for each digit’s common cathode, go to separate Arduino pins. The Arduino grounds one at a time to turn that digit on. Power: 5 V from the Arduino is fine; always use resistors to limit LED current. If you want a visual reference for pin locations, this page shows a typical 0.36″ 3-digit common-cathode display pinout:
Example code:
#include <SevSeg.h>
SevSeg sevseg;
void setup() {
byte numDigits = 3;
int segPins[] = {6, 5, 2, 3, 4, 7, 8, 9}; // a–g + dp
int digitPins[] = {10, 11, 12}; // cathodes for digits 1–3
bool resistorsOnSegments = true;
sevseg.begin(COMMON_CATHODE, numDigits, segPins, digitPins, resistorsOnSegments);
sevseg.setBrightness(90);
}
void loop() {
sevseg.setNumber(123);
sevseg.refreshDisplay();
}
Notes: Compared to the CircuitBasics example, you’ll add three cathode control pins and set numDigits = 3. The SevSeg library takes care of timing, brightness, and multiplexing for you. If your module has different pin numbering, use a multimeter’s diode test to identify which pin lights each segment.