PAGE 088 OF 150 · TIMERS, FLASHERS & DIMMING
LED Chaser Circuit
Lights step in sequence to look like motion.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Classic hardware chaser
A 555 provides clock pulses and a 4017 decade counter lights one of its ten outputs in turn. Each output drives an LED through a 330 to 470 ohm resistor.
Tips
- Connect the reset pin to the next output to shorten the sequence, for example to output 6 to use six LEDs.
- Change the clock speed with the 555 resistor or capacitor.
- Use 9 V so the chip outputs can drive LEDs comfortably.
Microcontroller versions are simpler and more flexible, using one pin per LED or a shift register.
REMEMBER
Switching an LED on and off quickly can look like steady dimmer light.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.