PAGE 103 OF 150 · DISPLAYS & INDICATORS
Large LED Clocks
Bigger digits need more current and careful power supply design.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Going big
Large clocks use several LEDs per segment, usually wired in series so one resistor serves each segment, on a 12 V or higher supply.
Design tips
- Choose digit height from viewing distance: doubling the distance needs roughly double the height.
- Drive segments with transistors or a driver such as the ULN2003.
- Estimate current: 28 segments at 20 mA each is 0.56 A with every segment lit.
Use a supply with spare capacity, and fuse it. Diffusing covers hide the individual LED dots.
REMEMBER
Series strings per segment keep current and wiring simple.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.
Explore LED clocks, stopwatches and electronics at cosycom.com.