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.

15 People Made This Project!

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59 Discussions

0
Quoc Quyen
Quoc Quyen

Question 4 months 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 4 months 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

5 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 4 months 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 5 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 4 years ago

its not blinking for me
can you plz help

0
tmichlovitch
tmichlovitch

Reply 4 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 4 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 4 years ago

its not blinking for me
can you plz help

0
Tycoon5000
Tycoon5000

10 months ago

This was actually a very helpful and useful little project to post. It helped in a project I was tasked with to increase hazard awareness in our lab, in particular, when we conduct a specific test that is potentially highly energetic. Signage can often be overlooked but this one really gets your attention. Helpful refresher of my basic electronics classes. Thanks for the post.

1
DevSUB005
DevSUB005

Question 1 year ago on Introduction

Could you pls upload a circuit diagram and an explanation as to how this works. Thx A MILLION

0
feraldrollery
feraldrollery

Question 1 year ago on Introduction

Do the capacitors have to be electrolytic, or would ceramic work?

0
feraldrollery
feraldrollery

Answer 1 year ago

And, what would I change to cause them to blink at different rates?

0
likeeachother
likeeachother

Question 1 year ago

What voltage are the capacitors used in this?

0
matelot2
matelot2

Answer 1 year ago

any capacitor with a voltage larger than the supply. The large voltage capacitor you use the large the capacitor will be phisically. Anything above 10 times the used voltage will fail, electrolitic capacitors don't work too well at 10% of their voltage rating.

0
keys-da
keys-da

3 years ago

This is a really useful circuit. Do you know what modifications I would need to make to get it to work using an npn transistor? Thank you.

0
matelot2
matelot2

Reply 1 year ago

google astable multivibrator. you will get lots of similar circuits, most of them with npn's

1
BreaV
BreaV

Question 2 years ago on Introduction

Could you add more LEDs? Per say 8-12? How would this change this circuit in terms of power supply and other components?

0
SergeyS85
SergeyS85

3 years ago

Thanks a lot for the nice guide!
And here is our circuit we've built today with my 7 yo daughter (she helped me a lot); we used different capacitors to make LEDs blink faster.

0
MrityunjayS3
MrityunjayS3

Reply 2 years ago

7 year old ! Re you kidding!! I'm struggling at 18 :(