Making a LED flasher

Note: The leds are actually very bright

This is a small project I was done with in about one hour(I didn’t found a use for it, but I’ll update the post if I do :D). It’s easy to build, especially for beginners like me. And the result is satisfying.

I used 2 blue leds, and I tested the circuit on my pc Power Supply. I found out that, although it’s designed for 5V, if I connect it to a 3,3 V line it will flash quicker.

Parts list:

  • 2x 5mm LEDs( I think it works best with blue\white leds)
  • 2x 330Ω resistors
  • 2x 22kΩ resistors
  • 2x 47uF capacitors( I used 16v ones)
  • 2x BC547C transistors( ‘universal’ transistors, they’re pretty common and easy to find)
  • a 4,5v-5v DC source(I used my power supply to test, but you can use 3 AA batteries)

Some pictures:

This project is so easy to build that I don’t really think it’s necessary to explain how to do it. But I’ll give you some indications if you really want to build it.

-When soldering it’s really hard to solder with one hand and hold the pieces together with the other hand. You need to use some kind of stand. If you don’t have one, you can improvise, like me :D. I used a pair of pliers with a rubber band on them so it can hold small pieces while I solder them.

-Be attentive to polarities.  For resistors it doesn’t matter(you can actually see in the pictures they’re not in the same direction). LEDs, electrolytic capacitors and transistors are polarized though. Be attentive to the schematic and solder them as indicated. Need help here too? Well here’s how to find the polarities:

  • LEDs: on the schematic, the negative part of the led is represented by a bar on top of that triangle. The other side of the LED(the one that, if you follow the wire, goes to the +5V input) is obviously the positive wire. Negative= Cathode, Positive=Anode. You know which is which because the anode wire is longer than the cathode. Also, near the cathode the LED is a bit flattened(it’s a bit hard to see).
  • Electrolytic Capacitors: this one is easy, because it’s written on the capacitor’s package(usually the negative side is indicated).
  • Transistors: This is a complex subject but I’m only going to clarify how to solder in the current situation. On the schematic you can see there’s an arrow on one of the wires. That’s the emitter. The middle one is the base, and the other wire is the collector. Because there’s no indication on the transistor, you need to consult the transistor’s data sheet. Here’s the BC547C  datasheet.

Ok, here’s the schematic:

2 Leds flasher Schematic
2 Leds flasher Schematic

I made the schematic using an open-source software: TinyCad !

Vodpod videos no longer available.

Have fun and have a nice day!


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