LFTT (LED Flashie Throwie Thingie)

About: Hi all, I'm a college student in the copenhagen technical college. I'm currently working with 3D printers and I'm building my own RepRap.
You may already know the LED throwies

The LED Throwies are very cool, however they could be a little more attention getting with just 2 extra components.

This Instructable will show you how to make a flashing LED Throwie.

Step 1: Parts List

To make one LED flashie you'll need:

a 10mm LED (I recommend, that you use a diffuse LED. I live in Denmark and the diffuse LEDs aren't available here, so I just used a waterclear type)

a CR2032 lithium coincell battery.

a Neodymium (NdFeB) disc magnet.

a LM3909 LED Flasher circuit

an Electrolytic capacitor (the bigger the capacitor is, the slower the LED flashes. I figured out, that a 100µF works fine. It will flash the LED at approx. 2.5Hz, while a 220µF will flash it with 1Hz.

Step 2: Solder the Capacitor Onto the LM3909

Now it's time to Solder the capacitor onto the LM3909 (see all the pictures)

Step 3: Solder the LED Onto the LM3909

Now it's time to solder the LED onto the LM3909 (see pictures)

Step 4: Cut Off the Unused Leads of the LM3909

Cut off the unused leads of the LM3909, so they don't short circuit.

Step 5: Solder Two Leads Onto the LM3909

Now it's time to Solder two leads onto pin 4 and 5 of the LM3909.

Step 6: Mold It (optional)

You can "mold" the circuit using a hot glue gun. This will make it water proof and shock resistant.

Step 7: Tape the Battery and the Magnet Onto the Circuit

Tape the battery and the magnet onto the circuit, just like you would do with an ordinary LED Throwie

Step 8: Throw It!

It's time to throw your LED flashie



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    50 Discussions


    10 years ago on Introduction

    Hi there. LM3909 IC's have been obsolete for at least the last 10 years :-(( Anyone know of a cheap source for these? Regards. Tony

    3 replies

    Hi there. Only picked up your reply now :-(  Apologies!! Would appreciate you finding out how many LM3909 IC's your local supplier has and at what cost.
    These chips have been unobtainable her in South Africa for the last 7 years :-(((  Thanks and regards.


    8 years ago on Introduction

    i agree with catman0321
    here is a instructable


    10 years ago on Introduction

    for anyone who needs forgotten LM3909!!! I found in a store here in Athens some boxes containing thousands of this IC, so anyone who wants some of them are available!!! costs 0,80 each

    2 replies

    Reply 9 years ago on Introduction

    Hi  there. Are these still available? If so what is the cost and how much to post to South Africa? Thanks and regards. Tony


    9 years ago on Introduction

    How much time should the batterie be alive??? I've made the same circuit and the first batterie ruined out in 1 week. I used a 100 µf / 25v capacitor and a ordinary red led diode.
    I've read the lm3909 datasheet and with a 1,5 v AA batterie it should be working for at least 6 month.
    What could be wrong??

    Thank you very much in advance


    9 years ago on Introduction

    Wow, how much radiation does that thing put out?!?!? In the video, it sounds like the geiger counter is going CrAzY!! lol!  Neat idea!

    1 reply

    10 years ago on Introduction

    You are only 14 years old, and can make better instructables than many adults. Keep it up, you'll make a lot of money one day!

    1 reply

    11 years ago on Step 1

    Hello there This is interesting but I do not know if you know, but there are in the market built in flashing LED and the cost of those are very cheap, the bad thing is I believe they comes in red and yellow but for the instance u can add this flashing leds in series to another color LED you want. You can find them in Digikey online. But is good though.