PAGE 104 OF 150 · DISPLAYS & INDICATORS
LED Stopwatch Display Basics
Fast refresh helps show hundredths of a second.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What a stopwatch needs
A stopwatch display counts time from a start press, stops on the next press and clears with reset.
Timing
- Use a hardware timer or the millis counter, not delays, so timing stays correct.
- Update at 100 Hz for hundredths of a second, and store the elapsed value as a number.
- Debounce each button for 20 to 50 milliseconds.
Show minutes and seconds with a decimal point, and add a lap button that freezes the display while timing continues.
REMEMBER
Count elapsed time from a timer, not from loop speed.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.