Introduction: LED Fox Pendant, Solar Powered Kit

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 cou…

This instructable is for solar powered Fox with amber LED eyes. It measures about 2 1/2" by 2 1/2", including the USB tab. It has one hole through the top of the board, making hanging easy. Wear it as a necklace, earrings, 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.

The schematic and parts list are included. You are welcome to wire up your own, copying is the sincerest form of flattery. We also have the kit available in our Store.

If you have soldered projects before, this will be easy. There are only 19 pieces to solder onto the board, and all are through hole. Depending on your soldering savvy it may take anywhere from 30 to 45 min. Watch it in action here!

Step 1: Tools

Here's what you need:

  • A soldering iron
  • Solder (with flux inside)
  • Diagonal cutters

Helping hands and needle nose pliers are optional, but helpful.

Step 2: Schematic and Parts

Schematic is above.

Parts list is below.

  • C2 - 47uF ceramic capacitor (bigger blue one)
  • C3 -10uF ceramic capacitor (little blue one)
  • C4 - 0.1uF Timing capacitor (TINY tan one)
  • U2 - MCP6542 dual micro-amp comparitor
  • SC1 through SC6 - BPW34 photo-diode
  • R5 - 330ohm resistor, orange bands.
  • R1, R2, R3, R4 - 10M resistor, brown and black bands
  • D1 and D2 - amber LED to blink
  • Switch - SPDT switch 3-pin 0.1 spaced
  • C1 - 0.033F black coin super cap

Step 3: Capacitors

Start with the three small caps. They may all look similar, but it is important that the correct one go in the correct slot.

BTW, these capacitors don't have a polarity, so once you figure out which goes where you can't install them backwards. Below is a short description of how to read the numbers on them, but for more detail check out this cool electronics wiki.

  • C2 is the bigger blue one. The tiny numbers on it read "476". The first two digits are the value, the third is the multiplier. Capacitors are measured in pico-Farads. So 476 is 47*10^6 pico-farads.
  • C3 is the little blue one, and has 106 written on the side.
  • C4 is the TINY tan one and has 104 written on the side.

SPECIAL NOTE: C4 should be soldered on the back side, as it sits really close to the board. Spread the leads as shown then flip the board over to solder on the back. Spreading the leads keeps the tan cap from falling out when soldering on the back side.

If you have never soldered before here are the basic steps. If you have, skip this part.

  1. Grip the cool handle of the soldering iron in your pencil hand and hold the hot tip where the capacitor lead (wire) touches the pad. The tip of the iron needs to touch BOTH the wire and the pad in order to heat up both.
  2. Hold it in place for 2 to 3 seconds.
  3. Touch the tip of the solder wire to the pad you just heated. If it is hot enough, you will see the solder melt immediately.
  4. It is important that the solder melts onto BOTH the resistor wire and the pad to create a connection. It will wet onto them like water.
  5. Once the pad and wire are covered in solder, remove the solder wire first and THEN remove the iron.
  6. Allow the solder to cool. Do not bump it until the solder is solid (it will still be hot). This will take a second or two and if you watch closely, you will be able to see the solder solidify.
  7. Repeat steps 1-6 for the other capacitor pad. Congratulations, you now know how to solder!

Step 4: Resistors

Next the resistors. They don't care about polarity either.

Bend the leads into a U shape so they fit into the holes. Pull them through the board so they are nice and tight.

We recommend starting with with R5, it's the orange odd one out. Check out this handy dandy link for how to read resistors. Unfortunately they are tough for color blind people to decipher. But, I hear there is an App for that. ;)

Again, solder from the top. You CAN solder from the backside if you bend the leads out, but be careful the resistors don't fall out. We prefer soldering from the top because it leaves the backside is smoother. The pendant is more comfortable to wear this way.

The remaining resistors R1 through R4 are all the same, brown black. Pull them through and solder them from the top as you did with R5.

We recommend flipping the fox over and trimming the leads at this point.

Step 5: Chip (BRAINS!)

Next the chip, the foxy brains. Probably not nutritious for zombies.

Be very careful of stray electric shocks, they may fry the chip. We know this from experience, ouch! Ground yourself before handling the chip by touching a large metal object first. We find the bolts on outlets are convenient and grounded

Line up the chip on the board, U1. The cutout and dimple on the chip should match the square on top of the board chip footprint. You can see it in the picture. You may have to squeeze the leads on each side to get it to snap in.

Solder on top as usual. You may also solder on the back, be careful to not solder the legs together.

Below is a video of what me attempting to solder with a dirty tip. Doesn't work so well! Much better after I clean it with the sponge.

Step 6: Mini Solar Cells (actually Photo-diodes)

Next the mini solar cells, which are actually photo-diodes used to sense light levels.

It really REALLY matters that these are put in correctly. The positive end is marked on the board with a +. The positive on the photo-diode has a TINY silver dot on top.

Match + with + on SC1 through SC6. Like with the chip, you may have to gently squeeze the leads together to make it slide into the holes.

These MUST be soldered from the top. They will fall out if you try to solder from the back. But by now you should be a pro, so no sweat.

This is a good time to trim the leads on the back again. Be careful with the tiny ones though, they can fly FAR. Aim away from your eyes or friends. Siblings are fair game though (kidding Marty!)

Step 7: Storage Cap

And next, the black storage capacitor. SUPER CAP!!! (No capes)

This puppy will keep your fox going for 3+ hours after dark.

Again, the orientation matters. The negative lead is labeled on the top of the cap by a - negative sign on the metal band. The positive lead is on the bottom and labeled on the board. Correct orientation is shown in the picture.

Solder on the top side as it may fall out.

Step 8: Switch and LED Eyes

The switch doesn't care which way you solder it in. WARNING: it is made of low temperature plastic and will melt easily if the soldering iron touches it. I know I know, melting plastic is fun, but please restrain, that will make it inoperative.

We recommend soldering the switch while the board is upside down. Rest the switch on the table so it doesn't fall out.

Now for the fun part, the blinky bits! D1 and D2 are the amber LED eyes.

The LEDs DO care which way they are soldered. Luckily it is easy to tell the polarity. The circle around their holes has a flat side, line this up with the flat on the base of clear plastic LED casing as shown. You can also tell which lead is which by their length. The positive lead is the longer one, and should be on the outside as shown

What is the best part about this step? YOU ARE DONE!

AND if you are in a bright naturally lit room and soldered it all correctly, IT WILL NOW BLINK! The LED's will run directly off the ambient light collected by the photo-diodes. Or for even more power, stick the USB tab into any available socket and they'll REALLY shine like below. WINNING!

Step 9: FUNction

The first time you charge your fox we recommend conditioning the super caps. What does this mean? Charge it above and beyond full capacity and store this for a few hours. It keeps the caps 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" Watch the video or use the directions below.

How to play:

  1. Flip 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. This connects the black storage capacitor to the circuit.

      a. USB – plug it in. Wait 2 minutes till its really, really bright. If the LED's are constant, its full. OR…

      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. Otherwise…

      3. Store the charge for later by flipping the switch to “Direct”.

      Endurance: In “Store” mode it'll run about 3 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 10: Extra Credit

      You are welcome to string up your winking fox as a necklace, 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 fox 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 fox 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. You MUST work fast, it gets gummy quickly 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. Avoid sealing the switch and USB tab. 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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