Simple Blinking LED Circuit
Simple Blinking LED Circuit

A very simple circuit that you can build to blink or flash LEDs. The circuit is built using transistors, resistors, capacitors, and LEDs. Of course you will need a breadboard, wire jumpers, and a power source. The parts list includes:

  • PNP Transistor, P/N 2907A, qty: 2
  • Resistor, value 470 Ohms, qty: 2
  • Resistor, value 100k Ohms, qty: 2
  • Capacitor, 10 uF, qty: 2
  • LED, Qty: 2
  • Breadboard
  • Jumper wires

    Let's get started:

    Step 1: Add the transistors

    Simple Blinking LED Circuit

    Add the two PNP transistors and the jumper wires from the power BUS to the emitter of each transistor. Because of the way I inserted the two transistors the emitter is on the left side of both transistors.

    Step 2: Add the capacitors

    Simple Blinking LED Circuit
    Simple Blinking LED Circuit
    Simple Blinking LED Circuit

    Connect the two capacitors to the circuit. Connect the positive lead of the first capacitor to the collector of transistor 2. Next connect the negative lead of the same capacitor to the base of transistor 1.

    Repeat the above process for the second capacitor. Connect the positive lead of the second capacitor to the collector of transistor 1. Connect the negative lead of the same capacitor to the base of transistor 2.

    Step 3: Add the 100K resistors

    Simple Blinking LED Circuit

    Next connect the 100k resistors to the transistors. One lead of the resistor connects to the Base of the transistor, the other lead connects to ground. Do this for both transistors.

    Step 4: Add the LEDs

    Simple Blinking LED Circuit
    Simple Blinking LED Circuit

    Finally add the two 470 Ohm resistors along with the two LEDs. I added a picture of a transistor to identify the Emitter, Base, and Collector.

    Connect one wire of the first resistor to the collector of transistor 1. The the other resistor wire then connects to the positive wire of the first LED. The negative wire of the LED is then connected to ground.

    Follow the same steps for the other resistor and LED. Connect one wire of the second resistor to the collector of transistor 2. The the other resistor wire then connects to the positive wire of the second LED. The negative wire of the LED is then connected to ground.

    Step 5: Supply Power and Watch the LEDs blink

    Simple Blinking LED Circuit

    The last step is to supply power and watch the LEDs blink. I use a 9 volt battery and it worked fine.

    For fun you can try other capacitor values to change the rate at which the LEDs blink.

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