74HC4511 BCD-to-7-Segment Driver

Drive a 7-segment digit directly from four binary signals — the original chip-and-a-display way to show numbers before TM1637 modules existed.

Difficulty: Breadboard. Estimated build time: about 22 minutes. Estimated parts cost: about US$3.20. 6-line bill of materials. Compare supplier offers when available. A single 7-segment display that lights up one decimal digit (0-9) based on a 4-bit binary input on pins A, B, C, D.

Wire the display segments

The 74HC4511 expects a COMMON-CATHODE 7-segment digit (cathodes tied together to ground). Connect pin a-out (pin 13) to segment a on the display through a 220 Ohm series resistor, pin b-out (pin 12) to segment b, c-out (pin 11) to c, d-out (pin 10) to d, e-out (pin 9) to e, f-out (pin 15) to f, g-out (pin 14) to g. Tie all the common cathode pins on the display to ground. Power the IC with 5 V on pin 16, ground on pin 8.

Wire the BCD inputs

Connect pins A, B, C, D (pins 7, 1, 2, 6) to four toggle switches with pull-down resistors (10 kOhm to ground, switch to +5V). Tie LT (pin 3) HIGH (disable lamp test), BL (pin 4) HIGH (disable blanking), LE (pin 5) LOW (latch transparent, chip follows inputs in real time).

Count through the digits

Flip the input switches through every binary combination 0000 to 1001 and confirm the display shows '0' through '9'. Try 1010 through 1111 — nothing should light, which is the BCD-invalid behaviour. Now briefly tap LT LOW — every segment turns on (lamp test, useful for verifying the display hardware). Tap BL LOW — every segment turns off (blanking, used to power-save between display refreshes in multiplexed designs). The whole chip costs $0.50 and runs forever; it's the textbook way to drive a single digit before you reach for a TM1637 or MAX7219.