Simple Blinking LED Circuit

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Introduction: 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:

  1. PNP Transistor, P/N 2907A, qty: 2
  2. Resistor, value 470 Ohms, qty: 2
  3. Resistor, value 100k Ohms, qty: 2
  4. Capacitor, 10 uF, qty: 2
  5. LED, Qty: 2
  6. Breadboard
  7. Jumper wires

Let's get started:

Step 1: Add the Transistors

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

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

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

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

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.

16 People Made This Project!

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70 Comments

0
DavidM681
DavidM681

Question 6 days ago on Introduction

Anyone out there clever enough to produce the same circuit but for 3.3v?

1
ChrisRC
ChrisRC

Question 9 months ago

Would this work on 5V or if it need some adjustment to work what would it take?
Thank you.

0
keerthan r
keerthan r

Question 1 year ago on Step 2

why are capacitors used in this circuit
?

1
tmichlovitch
tmichlovitch

Answer 1 year ago

The capacitors are designed to charge and then discharge, which allows the LEDs to flash.

0
anivia2409
anivia2409

Question 1 year ago

I dont know why my board did not blink. I used:
2 x 50V 10uF capacitors
2 x PN2222A transistors
2 x 330 Ohm resistors (I dont have 470 ohm so I used 330 ohm)
2 x 100k Ohm resistors
1 x 9V battery

Please help with diangosing it :(

IMG_1126.jpg
0
tmichlovitch
tmichlovitch

Reply 1 year ago

Using a 330 ohm instead of the 470 should be fine, that's not your problem. Is either LED turning on? Check the placement of the capacitors, there should be a (+) and (-) marking on them. Make sure the capacitor leads are correct. Also double check the pins on your transistors to make sure that they were placed correctly

0
phranki
phranki

1 year ago

would somebody have an idea how this could be altered to solar
power, so it could come on at night ?

0
phoenix98604
phoenix98604

Question 1 year ago

I would like to be able to use several of these circuits each to make random single blinks recycling over 1-2 minutes. Can the LED's be made to turn on softly and turn off softly to extend the blink time (1-2 seconds)/

1
tmichlovitch
tmichlovitch

Reply 1 year ago

I wouldn't know how to accomplish that with this current circuit. Not saying it can't be done, I just don't know how to do it. Look into using a micro-controller like Arduino, you will easily be able to have the type of control you want over the LEDs

0
Gina_ex
Gina_ex

Question 1 year ago on Introduction

Just a few questions:
1). Can this cct be expanded to make a design like a mini ( 6 - 8 ) multi-color LED Christmas tree ?
2). Would this - or a modified version - be programmable for random interval flashing of the LED's ,and if so what added components are required ?
What alternatives for power source are recommended, if any ?

1
tmichlovitch
tmichlovitch

Answer 1 year ago

I'm pretty certain you should be able to expanded the project to add more LEDs, but only by adding them in series to the existing circuit LEDs. So, if you added an additional LED to each circuit leg with an existing LED, then you could have 2 on and 2 off, flashing back and forth (instead of 1 on and 1 off flashing back and forth).

This is not programmable. If you're interested in programmable circuits definitely check out Arduino, Raspberry Pi, and others.

0
Quoc Quyen
Quoc Quyen

Question 2 years ago

Transistors have 3 poles E, B, C and its structure as 2 diodes in reverse. Why is the power source going from C to E without stimulating pole B? Please explain to me

anh.PNG
0
Vivian N
Vivian N

Answer 2 years ago

I think it's because the circuit uses PNP transistors, which stop conducting when current is applied to the base, hence why the lights blink when the capacitor discharges. If it used NPN transistors, there would need to be current going to the base for it to conduct.

0
tomatoskins
tomatoskins

7 years ago on Introduction

These look awesome! Electronics are great! I've never thought to use this type of circuit before.

0
Quoc Quyen
Quoc Quyen

Reply 2 years ago

Transistors have 3 poles E, B, C and its structure as 2 diodes in reverse. Why is the power source going from C to E without stimulating pole B? Please explain to me!!!

anh.PNG
0
tmichlovitch
tmichlovitch

Reply 7 years ago on Introduction

Thank you for the feedback. It's definitely fun to see what can be done with electronics.

0
VyashB
VyashB

Reply 6 years ago

its not blinking for me
can you plz help

0
tmichlovitch
tmichlovitch

Reply 6 years ago

My apologies, in my previous resoonse i said check your diodes when i meant to say check your capacitors. This circuit does not contain diodes.

0
tmichlovitch
tmichlovitch

Reply 6 years ago

If you chose the correct components my first thought is either the transistors or diodes aren't connected correctly. The diodes only allow current to flow in one direction so make sure they are proprly set.

0
VyashB
VyashB

Reply 6 years ago

its not blinking for me
can you plz help