LED Flasher with LM3909

This is a very easy and simple LED flasher with only three components: a flasher IC LM3909, a LED indicator and an electrolytic capacitor.

LED Flasher with LM3909

The supply voltage is 1.5V, so it can be operated using a 1.5V battery which can be easily found on market.

Component list:

LED1 _________ Red LED
C1 ___________ 100uf/16V
IC1 __________ LM3909
Battery ______ 1.5V AAA


The LM3909 is a monolithic oscillator specifically designed to flash Light Emitting Diodes. By using the timing capacitor for voltage boost, it delivers pulses of 2 or more volts to the LED while operating on a supply of 1.5V or less. The circuit is inherently self-starting, and requires addition of only a battery and capacitor to function as an LED flasher.

This circuit can be used for various applications:

  • Finding flashlights in the dark, or locating boat mooring floats
  • Sales and advertising gimmicks
  • Emergency locators, for instance on fire extinguishers
  • Toys and novelties
  • Electronic applications such as trigger and sawtooth generators
  • Siren for toy fire engine, (combined oscillator, speaker driver)
  • Warning indicators powered by 1.4V to 200V
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