Make a Flower LED

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...

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 Conrad.com. 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

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. 

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.

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!

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...

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.

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!