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...

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 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

Comments

[jsa2145]

here are the pics !
looks better in real life :)

[ynze]

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

Thanks for posting the pics, I REALLY appreciate it!

Y.

[jsa2145]

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

[jsa2145]

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

[ynze]

Good job!!! Can't wait for the pics!

[jsa2145]

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)

[ynze]

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?

[jsa2145]

"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

[jsa2145]

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)
thanks

[ynze]

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.

[jsa2145]

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 ?
thanks

[ynze]

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.

[jsa2145]

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 !

[ChrysN]

Neat!

[mischka]

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?

[ynze]

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.

Y.

[janw]

Looks great!!

[ynze]

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

[janw]

Speedy is my middle name! :P