Hello readers! In this Instructable, I am going to be detailing how to make your very own pulsating LED, just like the light on the top of the TARDIS! I am going to do my very best to explain this process, and why certain aspects of this circuit are designed in that particular way, as well as hopefully providing you with the knowledge that enables you to alter certain things in this build to match your liking. The inspiration for this project came when designing a clock face for my Resistant Materials GCSE. I wanted to make my clock look like a TARDIS, however, didn't want it to compose of just boring plastic. So, I decided to replace the top of my acrylic TARDIS with a pulsating LED. I then designed a circuit that could perform that very task (see the diagram above). So, without any further ado, let's get straight into it!

Before proceeding, I would like to just quickly recommend that you pay careful attention to the illustrative pictures provided on each step! They have detailed notes and will definitely help you with building and understanding this circuit!

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Step 1: Gather All The Parts!

OK, so let's start by gathering all the parts we are going to need. You should be able to pick these up on the cheap from your local big electronics store (US: RadioShack UK: Maplin Online:

For this build, you will need:

The Circuit:

  • Veroboard (Stripboard) (about a 12cm x 12cm area will suffice)
  • A switch
  • 5 x 330Ω resistors
  • 3 x 10kΩ resistors
  • An 8-pin IC holder
  • A 555-Timer chip
  • A 100uF (microFarad) capacitor
  • An LED (of any colour)
  • A BC108 transistor

For Power:

  • A 9 volt battery
  • A 9 volt battery clip

The LED:

  • Wire (and plenty of it: red and black)
  • Heat-shrink tubing of different diameters

Also (optional):

  • Squares of Velcro (optional - for finishing touches)
Dr_Becks made it!9 months ago
Nice Project! Works perfectly!

The circuit is just a Test on this Picture, i will improve this later.

I have used a another Transistor - BC548B

With a lower resistor - like 10k - the frequenz is better with this transistor. More Like the Tardis.

Doctor Who <3

robkirk made it!9 months ago

like the other guy i used a b548 and reduced the resistors to my liking.

Photo on 20-03-2014 at 12.49.jpg
Sam Naughton B (author) 9 months ago

It gives me great pleasure to hear that you actually made this! Thank you very much for your constructive feedback! I will definitely try it!

pfred29 months ago

Why did you need a transistor to drive the LED? 555 timer ICs can source, and sink quite a bit of current by themselves.

Sam Naughton B (author)  pfred29 months ago

Indeed they can. The principle is that all the current should go into the capacitor to charge it up (with the LED connected in parallel). Without the transistor, all the current would go into the LED and there wouldn't be any left to charge the capacitor!

The output pin of a 555 timer sources, and sinks current depending on what state it is in. You're only charging your capacitor on the source phase though. That leaves you a whole phase that does nothing unless you polarize a component to take advantage of it. So if you connect the cathode of an LED to the output pin of the 555 timer it does not affect your capacitor's charging rate at all. With the current capacity of a 555 timer you're not going to significantly affect your charge rate with the LED reversed either.

The 555's Threshold, and Discharge pins are for controlling your timings. The most produced chip of all time really is a brilliant little piece of work.

Sam Naughton B (author)  pfred29 months ago

A valid point. You are correct. Normally you would indeed use the OUTPUT pin of the 555 Timer. However, this would make the LED either be ON or OFF. We don't want this: we want the LED to fade in and out. The output pin in used via a 20kΩ resistor string to control the charge/discharge cycle.

fazmi29 months ago
i have done study about this circuit on my diplomA . simple principle . :)
diy_bloke9 months ago

nice, that is a big piece of board though for a few components :-)

Sam Naughton B (author)  diy_bloke9 months ago

I agree! I could probably fit this entire circuit onto a piece of board just about 2.5cm x 2.5cm, however, I spread the components out quite a bit for illustrative purposes!

I understand. didn't want to criticize :-). nice project

flamousz9 months ago

what is tardis clock ? what it for . thxx

Sam Naughton B (author)  flamousz9 months ago

Basically, I'm multi-cutting pieces of flat acrylic to look like the front of the TARDIS. Then I will drill a hole and thread a clock mechanism throught! I hope that helps!

ok thanks for help :D
Sam Naughton B (author) 9 months ago
Thanks, that's a really good idea! I had not thought of that!
Kiteman9 months ago

Can we see it in the actual clock?

Sam Naughton B (author)  Kiteman9 months ago

Absolutely! However, I am currently still in the process of multi-cutting some of the final layers of the clock as I have had restricted access to the workshop! I plan on vacuum forming around the LED to put it into the clock. All of this will be detailed, and added to this Instructable when it is finished! Thanks.

That's cool, but it might be worth writing a fresh instructable for that, since this instructable will have slipped into the past a bit by then.

You can include a link to this project in your new project.