MAX7219 8×8 LED Matrix Display
Drive a 64-LED dot-matrix display from three Arduino pins via the MAX7219 SPI driver.
Difficulty: Through-hole. Estimated build time: about 50 minutes. Estimated parts cost: about US$7.00. 5-line bill of materials. Compare supplier offers when available. An 8×8 LED matrix scrolling display driven by a single MAX7219 in DIP-24.
Place the driver
Insert the MAX7219CNG (DIP-24) across the breadboard's center divider. Pin 1 is V+, pin 4 is GND, pin 19 is V+ as well — tie both V+ pins together to +5 V and pin 4 to ground.
Set the LED current
Connect a 10 kΩ resistor (RSET) between Iset (pin 18) and V+. This resistor sets the peak per-segment LED current — 10 kΩ is approximately 40 mA peak, which is near the chip's maximum. Use a larger resistor (say 33 kΩ) for a dimmer display that runs cooler.
Wire the SPI interface
Connect Arduino pin 11 (MOSI) to MAX7219 DIN (pin 1); Arduino pin 13 (SCK) to MAX7219 CLK (pin 13); and Arduino pin 10 (any digital output works) to MAX7219 LOAD/CS (pin 12). Connect Arduino GND to MAX7219 GND.
Connect the matrix
An 8×8 common-cathode matrix has 16 pins — 8 rows and 8 columns. Wire the matrix's row pins to the MAX7219 SEG A–G,DP outputs (pins 14–17, 20–23) and the column pins to the DIG 0–7 outputs (pins 2, 3, 5–11). Many through-hole matrices have a non-obvious pinout — check your matrix's datasheet (or test each pin with a 1 kΩ + 5 V probe) before soldering.
Drive it from code
Drop a 100 nF ceramic between V+ and GND right at the MAX7219, plus a 10 µF electrolytic on the supply rail. In Arduino IDE, install the LedControl library, instantiate `LedControl lc(11, 13, 10, 1)`, then `lc.shutdown(0,false); lc.setIntensity(0,8); lc.clearDisplay(0);`. Now `lc.setLed(0, row, col, true)` lights any pixel. Drawing text means writing one row at a time. Power up — pixels appear instantly with no flicker because the chip multiplexes at roughly 800 Hz.