PAGE 081 OF 150 · TIMERS, FLASHERS & DIMMING
Flashing LED Alternator
Two LEDs can take turns blinking.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Alternating two LEDs
A 555 astable circuit makes an alternating flasher with one chip. Connect one LED and resistor from the output to ground, and a second from the supply to the output.
Operation
- When the output is high, the first LED lights.
- When the output is low, current flows from the supply through the second LED.
The pair swaps at the astable rate. Use a resistor for each LED, such as 470 ohms on 9 V. The same effect can be coded on a microcontroller using two pins, which is useful for emergency-style lights and warning signs.
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.
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