Solar Powered SM SKULL Blinky LED Jewelry




About: We’re life-long tinkerers, siblings, and fourth generation engineers. We’re not quite sure which of us had the idea of putting LED’s on jewelry and powering them with solar cells, but once Marty proved it c...

Ready to up your soldering game and try some SMD's? Disappointed with the boring "learn to surface mount solder" kits that do nothing and look lame? Well we've got your answer, with our blinky Skull surface mount soldering kit. Not only will your nerdy skills improve, but you'll have something to show for your efforts at the end. Makes a great geeky jewelry gift. We have several other soldering kits, check out our store.

The skull measures 1" by 3/4", about the size of a quarter. It has two alternating red LED eyes that are solar powered. There is also a micro USB connector on the back if you want to quick charge it. The board has a hole through the top, making hanging easy. String it up as a necklace, earrings, make a keychain, bond on a pin, or hang it in a window. The possibilities are up to you, and we'd love to see what you do with them. Watch it in action below.

This instructable gives step by step instructions on how to assemble the surface mount blinky skull. Sparkfun also has some great tutorials for the fine details of surface mount soldering. Honest, with the right tools it is as easy as they make it look. This kit is NOT for the beginning solderer (is that a word? I think it is), but should only take about 45 minutes for an intermediate.

The schematic and parts list are included. You are welcome to wire up your own, copying is the sincerest form of flattery. But why would you want to when we also have the kit available in our Store, that, did I mention, looks like a SKULL?


Step 1: Tools

There are a few extra tools that make surface mount soldering much easier. Sparkfun has a good list, here is what we recommend.

1. Good lighting, its essential
2. A Magnifying glass. These parts are tiny, and unless you have go-go-gadget eyes you'll need one.
1. One of those combination magnifying lights. Solves two problems with one gadget.

Oops, now the numbering may be messed up. Oh well, you get the idea.

3. A static free or dissipative surface. Surface mount soldering components can be very sensitive to stray electric shocks, especially the chips.
4. Tweezers, self explanatory.
5. A good quality fine tipped soldering iron. Like sparkfun says, spend the money on a $50 one with decent temperature control.
6. Small solder (0.032" or smaller)
7. Solder wick, 1/8" wide or less. 1/16" works best for this project.
8. Liquid flux
9. Exacto knife
And last but certainly not least
10. Your handy dandy diagonal cutters

Step 2: Parts List and Schematic

To help keep everything straight, we put the smaller pieces into a weekly pill organizer. Some of these parts look exactly alike, so staying organized is important. We also included a lot of detailed pictures of each component. The kit comes with one extra of everything in the pill organizer, just in case. If you're good you will have parts left over.

Below is the parts list, in order of instructable assembly.

There are two versions of the circuit board. They will be labeled on the back with Skull05 or Skull06. Below are the parts common to the two versions.

Common Parts

Qty Part
3 C5 and C6, 1uF 0805 (Wednesday)
3 C2 and C3, 10uF 0805 SM (Thursday)
2 R1, 2.0Meg 0805 (Saturday)
3 R2 and D5 (or R3 on rev 6), 300ohm resistor (Friday)
3 D1 and D2, Schottky diode (Tuesday)
3 D3 and D4, SM red LED (Monday)
4 SC1-SC4, BPW34 solar cell
1 Switch
1 Micro-usb-b connector

Below are the parts that changed from version 5 to 6.

2 U1, 74LVC2G14 (Sunday) The rev 05 chip is smaller than the rev 06 chip. See pictures above.
1 C1, 0.2F silver super capacitor for rev 5 or 0.33F black Super cap for rev 6. See pictures above.

There are also two versions of the circuit board, labeled on the back.

Step 3: Capacitors C6, C5, C2 and C3

We'll start with capacitors C5 and C6. They are in the Wednesday compartment. The orientation doesn't matter on these parts. The label for C5 and C6 is on the back of the board for rev 5, and on the front for rev 6, so make sure you're soldering on the correct one. The basic steps for surface mount soldering go like this.

1. Tin one of the pads
2. Grab part with tweezers
3. Place part correctly onto board, holding it with the tweezers while melting solder onto one end of the part.
4. Remove soldering iron from melted solder but continue to hold part with tweezers until the solder has solidified.
5. Solder on the other end of the component. Its best to be quick when soldering the second end so the first pad doesn't melt as well. Don't worry if that happens, SMD components are so small that the solder surface tension will keep it in place when you carefully remove the soldering iron. A video of soldering the first cap is below.

SM skull solder.mp4 from Robin Lawson on Vimeo.

One thing to remember about surface mount soldering; you can easily rotate the board. I have rotated the pictures to make them easier to understand, but in reality the skull was hardly ever head up as shown in the pictures. It was practically spinning around like a top while soldering. This made accessing the pads easier and more comfortable.

Next capacitors C2 and C3 in the Thursday compartment. Again the label is on the back for rev 5, front for rev 6. They are the two teeth in between the previous capacitors. Repeat the same steps: solder a pad, solder one side of SMD cap, solder remaining pad.

Step 4: Resistor R1 and D5

Next the final tooth of the grin, R1 in the Saturday compartment. Repeat the same steps: solder one pad, solder one side of the resistor, solder remaining pad.

D5 on rev 5 is the same as R3 on rev 6, they are both a resistor. Its 300 ohms from the Friday compartment. By now you should have the rhythm of surface mount soldering down.

Step 5: Diodes D1 and D2

Next the Schottky Diodes in the Tuesday compartment. These are the first components where the orientation matters. Good lighting and a magnifying glass will help you see the detail. The three parallel lines are the easiest to see, they go AWAY from the 'A' on D1 and D2. Double check the orientation after soldering. If you mess up, the first few steps of this Sparkfun Tutorial show you how to remove components.

Step 6: Red LEDs

And now, the BLINKY BITS!!! They're in the compartment for Monday. The orientation of the LED's is super important. As shown in the pictures, there is a green 'T' on the back of the LED. The top of the T goes towards the 'A' on the board. On the top of the LED there is also a really small green dot. This dot faces AWAY from the A on the board. Again, a magnifying glass is very helpful. Solder as usual.

Step 7: Photo-diodes A.k.a Mini Solar Cells

Last step for Rev 5 on the top side are the photo-diodes (mini solar cells). They are loose in the bag, you should have 4 of them. The orientation of the photo-diodes is also important. There is a small silver dot on one end that indicates the positive. Double check with our pictures if you are unsure. Solder onto the solar cells S1 through S4. Please note, the orientation switches on S2 and S4, the silver dot faces towards the bottom of the board.

Step 8: Chip!

Time to do the back side. Flip the board over, and now the hardest part begins, soldering on the chip. They're in compartment for Sunday, and we included an extra just in case. The correct orientation is shown below. For rev 5 the end with the horizontal line goes up towards the U1 label. For rev 6 the letter H is on top.

1. Tin 1 or two of the pads. Don't worry if they get bridged, we'll fix that later.
2. Using tweezers, hold the chip in the correct location.
3. Melt the tinned pads, soldering the chip in place. Keep holding it in place with the tweezers when you remove the soldering iron until the solder has solidified.
4. Solder the remaining pads.

Now you may have some bridged leads on the chip as shown. This is easy to fix with our handy dandy liquid flux and solder wick. YiHaw! This method is called the smash and grab by spark fun, but I'm sure there are other names.

1. Dip the solder wick into the flux. You don't need much flux, so make sure you clean the excess off the wick. We used WAY too much, but it still turned out OK. We can clean the flux off later.
2. Place the solder wick on one side of the chip, and melt the solder underneath with the iron as shown. Don't leave it on too long, the wick is very absorbent.
3. Repeat step 2 on the other side on a new part of the solder wick. None of your leads should be bridged now. TaDaa!

Step 9: Switch, Storage Cap, and Final Resistor

Next the switch. It has two pins on the backside that fit into the holes in the board. This makes soldering super simple, it holds it in place.

Next the super cap, C1. For rev 5 it is silver and rev 6 it is black. This is the main power storage for your skull. The orientation for this one is easy to tell, the positive pad is labeled on the board and the negative lead is labeled on the cap.

Cap soldering for Rev 5

Tin one lead as shown, solder on the cap as usual.

Cap soldering for Rev 6

Bend the leads out flat and trim them as shown. Solder them to the board as usual.

And lastly, R2 in the Friday compartment. For Rev 5 R2 is on the back next to the cap. For rev 6 it is on the front under the solar panels. The orientation of R2 doesn't matter, so just solder it on like the pro you now are.

Step 10: Micro USB

Finally, the Micro USB-b. This part is also a little tricky to solder on.

USB for Rev 5

The rev 5 USB is surface mount, so its a little harder to attach. First, tin the pads as shown. Next, line it up as shown, making sure the two thin rectangular pads in the center line up with the outer gold plated USB leads. Secure the two large corners of the connector while holding it in place with the tweezers. Next carefully melt the two thin rectangular tinned pads onto the gold plated copper leads as shown. We don't use the middle 3. If they get bridged together, use the solder wick and flux again to remove the bridge. Finally, you want the USB to be very securely attached to the board. So go back and add more solder to the 4 corners. We included plenty of pictures to help you.

USB for rev 6

The rev 6 USB is mostly through hole, making it a little easier. Start with the thin gold colored pads in the center that carry the power. Add a solder pillow to one of these pads on the board and line them up, making sure the two thin rectangular pads in the center line up with the outer gold plated USB leads. Secure the two large corners of the connector while holding it in place with the tweezers. Next carefully melt the two thin rectangular tinned pads onto the gold plated copper leads as shown. We don't use the middle 3. If they get bridged together, use the solder wick and flux again to remove the bridge. Finally, you want the USB to be very securely attached to the board. So go back and add more solder to the 4 corners onto the through hole legs of the USB.

YOU'RE DONE!!! For more projects like this check out our website.

Step 11: FUNction

The first time you charge your skull we recommend conditioning the super cap. What does this mean? Charge it above and beyond full capacity and store this for a few hours. It keeps the cap from having a memory and undercharging. We also recommend cleaning off the flux with orange clean. The flux may corrode the leads over time. See the next step for details.

But you are probably impatient to PLAY WITH THE BLINKY!! We understand. Skull operation is super simple. It has two modes of behaving controlled by the switch. We call them "Store" and "Direct: The switch connects and disconnects the power storage capacitor.

How to play:
1. Switch into “Direct” mode. The piece now gets its energy directly off the surrounding light. If it’s dark, NO blinky. If it’s bright, blinky awesomeness for all!
2. Not all light sources are the same, have fun figuring out which ones make the piece blink.

How to charge:
1. Switch into “Store” mode.
a. USB – plug it in. Wait 2 minutes till its really, really bright. If the LED's are constant, its full.
b. Solar – find a light source it likes and leave it under for 10-15 minutes. See step 2 of “How to play” to figure out what light it likes.
2. Enjoy the blinky awesomeness now.
3. Store the charge for later by flipping the switch to “Direct”.

Endurance: In “Store” mode it'll run about 1.5 to 2 hours on a full charge in complete darkness. In “Direct” mode it'll blink as long as the room is bright. It's powered by SCIENCE!

Cleaning: Wash it with a warm damp soapy cloth. It may stop blinking when wet, don't panic. Let it dry out and it will start blinking. Do NOT put it in the dishwasher or washing machine (if you can help it). Both are too hot and may damage components.

Step 12: Extra Credit

You are welcome to string up your blinky skull as a necklace, pair of earrings, key chain, or simply window dressing. You can also bond a pin onto the back and wear it on a backpack or shirt. However, make sure there is an insulating layer of epoxy or glue between the metal pin and the back of the circuit board. The skull is very low power, and can easily be shorted out by touching the back (or sweating on it, ew.) A metal pin will short out the square and it won't work properly.

If you want to go the extra mile you can seal it in epoxy, which is easy to do. Here's how:

1. Clean it. Its best to remove the solder flux before sealing, so it doesn't discolor over time or corrode the metal.
a. The project must be completely dead before cleaning. Let it run down overnight or in a dark place, and keep the switch in "Store". Then when cleaning flip the switch to "Direct" so it doesn't re-charge.
b. We recommend full strength orange clean and a toothbrush to remove all the flux. Scrub it thoroughly.
c. Rinse with cold water
d. Allow it to dry overnight.

2. After cleaning, do your best not to touch it with your fingers. Rubber gloves are recommended. The oil on your skin may discolor the metal, and interfere with the epoxy adhering to the parts and board.

3. Clear 5 or 10 min epoxy will work great for sealing. Just work fast, it gets gummy quick and hard to work with. Mix up a small batch, not more than an ounce. You can always mix up more if you need it.

4. Using a disposable brush seal one side. On the backside, avoid getting any epoxy on the switch and USB. Everything else can be covered with epoxy and continue working, even the photo-diodes.

5 Allow the epoxy to completely cure. You'll know its done when it stops being sticky. This usually takes 24 hours, however don't be too impatient as un-cured epoxy will retain your finger prints. You want your blinky to be shiny don't you?

6. Repeat steps 4 and 5 for the other side. You're done!



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    8 Discussions


    5 years ago on Step 2

    Hello, are your photodiodes BPW34 SMD's? or not , I could not find the BPW34 in Farnell shop on SMD, I found those : BPW34S, are they the same?

    Or Do you know another product like this one or even more effective.


    5 replies

    Reply 5 years ago on Step 2

    Yes we use the BPW34S from Vishay for this piece. They're cheaper and work slightly better than the similar BPW34S parts from Osram. The original BPW34 has been cloned and repackaged in many ways. All the variants of the BPW34 photo-diodes are electrically interchangeable for this circuit. The package is the only incompatibility.


    Reply 5 years ago on Step 2

    Hello again and thx for this reply

    Do you know another product like this one, BPW34S but more effective?

    more amperage on out for instance and with the same size?


    Reply 5 years ago on Step 2

    The closest I've found are the IXYS solar bits. They have impressive power density, but cost a lot. IXYS used to sell the bare dies, so if you have access to a wire bonder that's another option. I've yet to find a larger photo-diode that's as cheap as the BPW34. Custom cut solar cells are another option, though I don't know if they can be cut small enough.

    What light source are you planning to charge under? The BPW34 (or any crystalline Si solar cell) doesn't work well under high efficiency light sources.


    Reply 4 years ago on Step 2

    Thank you so much for this! I'm planning to put white leds, for now i use 8 BPW34 for 4 leds, but it's week. I'm pretty bad in english what is a wire bonder and a bare dies? thx again


    Reply 4 years ago on Introduction

    "bare dies" would be un-packaged semi-conductor chips.

    If you've seen a PCB with a black plastic blob in the center the manufacturer bought un-packaged semi-conductor chips, used a wire-bonding machine to make electrical connections, then protected everything under a blob of epoxy.


    5 years ago on Step 12

    Do you have a preferred epoxy for potting with, or just any clear compound from the adhesive section of your local hardware store?

    1 reply