Make a Flower LED




Introduction: Make a Flower LED

About: Also have a look at member Monster-Marit. She Rocks (I'm a bit prejudiced, though :-))
A flower that lights up when put in soil. It also comes to life when put in water, or by just holding both bare ends of the "stem". So the leds become flower leds, so to speak. And if the leds were power leds, then this would be a flower power led project.

The circuit lighting the flower is a very easy one. If you're just starting with electronics, this might be a nice project to begin with. There's only five components and 4 leds to be soldered.

Have a look at the video to see how it works...

Video not playing? Have a look at it here...

This flower led is just a beginning. Pic number 4 is a sketch of a possible next version. If you like it, give it a try...

In the next six steps, I tried to make clear how to make such a flower led. The comments with the pictures tell about the same story as the texts in the steps. If you decide to make a flower led, please post a picture of it in the comments. I'd love to see what you made. Have fun!

Step 1: Stuff You Need

To make a flower LED, very basic electronic stuff is needed. I used less material than shown in the pictures.

All parts can be obtained in a one-stop shopping effort: Euro's, visit Americans, shop at Radio Shack.
Total costs should not exceed €7 / US$ 10

For the circuit:
  • 2x 10mm red leds
  • 4x 2mm green leds.
    (Use what you like and what you can make. I experimented a lot before I decided to use the leds mentioned...)
  • 2 Transistors, BC547B
  • 2 3 Volt Lithium coin cells. Bigger is better, I used model CR2450
  • 2 battery clips
  • 2 resistors: 39 kOhm, 1 MegaOhm
  • 1 Electrolytic capacitor: 2,2 µF

For the leafs and the stem:
  • Solid kern copper wire, about 60 cm (24")
  • Stranded kern (supple) copper wire, about 10 cm (4")
  • Jumper wire (not on the picture), for the flower's "stamen"
  • Prefab circuit board (see pic 4)
  • Small tie-raps

Tools needed:
  • Soldering iron and solder
  • Third hand
  • A breadboard for prototyping
  • Scissors or a sharp knife
  • Multimeter for prototyping
  • Small pliers or a multi-tool
  • Power drill and a 1.5 mm drillbit

Step 2: The Circuit - Prototype It!

The circuit powering the flower is often used in electronics tutorials, for demonstrating the use of a transistor as a switch. I used (almost) the same circuit in a previous Instructable: Blinky the LED pet.

If you're relatively new in electronics, build the circuit on a breadboard first.

Experiment with the leds: Different colors and models of leds have a different voltage drop and take a different current to glow brightly.

When starting with a type of led, always put a resistor of 800 Ohm in series with it. When the led shines only dimly, lower the resistance. For my circuit, it turned out that two leds in series were enough to limit the current to the right amount. In picture two, the two small red leds in series needed an extra resistor of 330 Ohm. All other leds are connected in pairs, in series. Keep in mind that the leds have a "plus-side" (anode) and a "minus-side" (cathode). With _most_ leds, the anode's lead is a bit longer than the cathode's lead.

With picture 3: If you like, you can use many leds, connected parallel. 

Step 3: Making the Leafs - Part 1

The leafs (or petals?) of the Flower Led are pieces of circuit board. The shape of the petals is completely up to you, as long as you make sure all the components will fit. Looking back, I'm not very happy about the shape I chose. But hey, it's a prototype :)

I added a pdf (A4, and US Letter for people on the other side of the Atlantic) you can use to lay out the shape of the petals and the components of the circuit board. The leads in the pdf are drawn scale 1:1, so print the file on 100% magnification. Also added are empty pcb-layouts, so you can draw your own leaf-shapes.

I used solid kern copper wire to connect the petals and for the stem. Since the copper kern is too wide to fit through the pcb's holes, I had to drill the holes wider, using a 1.5 mm drillbit.

I committed a crime by soldering the components on the copper-side of the circuit board. I know that. I did it because of the looks of the flower. It makes the soldering a bit tricky, because the risk of shorts between the copper leads is HUGE, this way.

So, if you're not very sure about your soldering skills: Do it as it should be done. Stick the components' leads through the GREEN side of the circuit board, and solder the leads on the copper-plated side...

With picture 4: If you want the components on the inside of the flower, like I did, bend the components leads in a straight angle, so the leads will be above the copper leads when soldered.

Picture 5: Attach the stem. Cut two leads of 25 cm (10") of solid kern electrical wire, and solder them in the appropriate spot on the board. In the picture, the leads are soldered on the wrong side of the board. I changed this later on, but didn't make a picture of it...

End with soldering the jumper wires that make the stamen of the flower.

Step 4: Making the Leafs - Part 2

The petals holding the batteries are easy to do:
Start with drilling holes wider, if you use thick solid kern copper wire.
Then solder the battery clips on the circuit board. You can't short the leads here, because the solders are far apart on the board :)

Then connect the Plus-lead of one battery to the Minus-lead of the other battery, using solid kern copper wire or jumper wire.

So now you have three petals, with components and leads. Time to put things together!

Step 5: Connecting the Leaves

The petals are held together by short pieces of copper wire. Connect the battery-boards first (previous step), and then connect the batteries to the main circuit board.

I used thick solid kern copper wire to be sure the petals are held together firmly. With hindsight, I THINK that jumper wire might do the job as well...

Step 6: Make the FlowerLED

Finally! In this step, the actual flower-led is made. It's not very complicated. The leds are soldered "free form", not mounted on a circuit board.

Picture 1: Start with soldering the leds that are connected in series. Keep in mind that the leds have a "plus-side" (anode) and a "minus-side" (cathode). With most leds, the anode's lead is a bit longer than the cathode. To connect the leds in series, solder the anode of one led to the cathode of the other led.

Picture 2: All the leds soldered together, making the flower led. Two pairs of green 2mm leds and a pair of 10mm red leds are connected parallel (parallel means that the plus-sides of the led-pairs are connected, and the minus-sides of the led-pairs).

Pictures 3, 4, 5 and 6: Prepare the stamens' tips to hold the leds: Bend a small loop in the bare tips of the leads, using a plier. Then solder the loops together. I used a crocodile clip to keep the leads together, while soldering.

Now solder the led-flower to the stamens' leads. Be sure to connect the leds anodes to the stamens' plus-lead (the yellow lead in picture 6).

Now, test your led-flower. Load the battery-clips with batteries, and hold the bare ends of the flower led's stem. The leds should glow up...

When they don't, don't panic! Check the connections, and check your circuit carefully. Check whether each component is connected as it should be in the schematic. You'll find the glitch, in the end. This kind of debugging comes with every electronics project, it's part of the game.

Step 7: Finish Up, Add Thorns.

Actually, you're done now. You have a working flower led. To finish up, tie up the stems' two leads with small tie-raps. When you cut short the protruding strips op plastic, the tie-raps around the stem look like thorns.

That's it. If you made it this far, please post a picture of your Flower Led in the comments.

Enjoy, and thanks for reading!



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    19 Discussions

    It's GREAT! Where did you hide the pcb's?

    Thanks for posting the pics, I REALLY appreciate it!


    I didn't use pcb's. I just soldered the components together with wires. the resistors for the leds are hidden in the electrical tape below the button (I made holes in it to hold the leds). The rest of the circuit is below one leaf and batteries below the other leaf. I wanted the flower to look a little bit more "natural" so I made the leaves from green paper. I hope my girlfriend will like this little gift !
    thanks a lot for your help and your tutorial

    Yess ! it's finally working :) I bought the same transistors as you on internet and it solved the problem (lowering the resistor value didn't work). It's now shaped like a flower, but I still need to make it a little bit nicer. I'll post pics soon
    thanks for the tutorial

    1 reply

    hi, is it possible that you made a mistake in the schematic ? because I did a similar circuit (using 2N3904 transistors) but the LEDs only light up slightly. I figured out that they should be placed beteween the second transistor and the ground (or the two-times-amplified current won't go through them). When I do this, they light up almost correctly (still not completly)

    2 replies

    You're actually building it! Great!

    What might help is changing the 39kOhm's value into something a bit smaller. Try 22kOhm (or 10kOhm) , and see what happens... 

    Placing the Leds between the second transistor and ground is fine, but shouldn't make a difference... The 2N3904 you use has a "voltage drop" of about 0.65 Volts, which is a bit higher than the BC547 I used (with every transistor you use, you lose 0.65V of the battery's voltage).

    > (or the two-times-amplified current won't go through them)
    When a (very small) current is fed into the base (middle lead) of a transistor, the transistor starts conducting current from the collector to the emitter. For the leds, it's not important whether they're connected between the +voltage and the collector, or between the emitter and ground. The current through the leds will be blocked either way, when there's no current fed into the second transistor's base.

    Maybe the specs of the leds you use are a little different than mine?

    "For the leds, it's not important whether they're connected between the +voltage and the collector, or between the emitter and ground"

    that's what i tought after posting, but I decided to wait for your reply instead of maybe posting another wrong thing ahahah. I guess the difference I get is due to the fact that the emitter current will be base current plus collector current (I think (kirchof law)) so maybe there is a very small difference of current.

    I will try to lower the 39K resistor.
    thanks for your help

    Hi, this tutorial is amazing ! the only problem is that I don't understand why you use two transistors. Wouldn't only one do the same thing ?
    (sorry I'm new with transistors)

    4 replies

    It would, if another (more sensitive) type was used. The BC547 I use is a very common, very cheap (€0,07 when bought in 100's) transistor.

    The BC547 amplifies a signal (current) about 400 times. Because the resistance between the leads / stems is very large (MegaOhms), the current between the stems will be very small. To amplify that small current into something that wil light up the leds, two BC547's are needed.

    hi, would the circuit work correctly if I use a 9V battery (or 3x3V), put something like a 100Ohm resistor in series with the battery and instead of using two LED in series (in parallel with the others two LED in series), I use three LED in series ?

    That might work. Just try it on a breadboard. If you're anxious to blow up the leds, start with a bigger value (1kOhm or so). When the leds light up only faintly, lower the resistor's value.

    thanks for your fast reply ! I think I understand. You decided to put a very large resistance between the leads / stems to be sure the current between them is small ( because a high current could be dangerous if someone touches the water (if the leads / stems are in water)). That is why we need to amplify "two times" the current. If we put a smaller resistor, only one transistor is needed, but the current between the leads / stems will be higher.
    Am I right ?
    sorry for my english.. and thanks for your help !

    Looks nice, I would cover the PCBs with some decorative paper flowers to make it less geeky, but I guess you did it for geekness. How long do the batteries last?

    1 reply

    Yup, I didn't want to cover-up the pcb's. But I agree that it looks a little too geeky now. I'm working on a version 2, with better looks...

    The batteries last about 4 days non-stop.


    I posted this about two seconds ago :D You're really a fast guy, aren't you?