How to build a simple blinking led circuit with a Here’s how you blink an led with just an led, capacitor, transistor and two resistors. This post is a complement to Dick Cappel’s “Simplest LED Flasher Circuit” post. I’ve added a Fritzing diagram and some high-res photos and video so that you can quickly build the circuit. Most of the other videos online are from a very long time ago and are mostly out of focus. How to Build an LED Flasher Circuit with a 555 Timer Chip The schematic diagram of the LED flasher circuit we will build is shown below: This circuit will flash the LED on and off, on and off. The rate that the LED flashes is determined by the resistors R1 and R2 and the electrolytic capacitor C1. Again, the output of a 555 timer are square waves.