Solar Necklace

What if you could harness the power of the sun to make your accessories glow (quite literally)? Mini solar panels made it possible for us to explore this idea through this project. The goal behind designing this necklace, as for every project in this series, was to connect eTextiles or soft robotics and circuit interfaces with sustainable power sources. Having solar panels accessible in scale and size that allows us to integrate them into flexible forms such as wearables opens a new door in the DIY technology trend.

While this application affords various benefits in terms of flexible and creative applications, the drawback is that mini solar panels generate very low voltage. This necklace utilized 60 mini solar panels, arranged in a circuit that outputs 9 volts around 0.3 amperes in full sun. Despite that limitation, we chose mini panels, because they allowed greater physical flexibility for the garment. Check out our other solar content to see different panels.

This tutorial will cover:

List of materials you will need
Design of the necklace and circuit arrangement
Link to the laser-cut file for the necklace

Step 1: Soldering the nickel strips
Step 2: Laser cutting instructions
Step 3: Laying out the wiring for the solar panel circuit with conductive tape
Step 4: Sewing the panels in place
Step 5: Testing the circuit output in the sun
Step 6: Sewing in the Neopixels
Step 7: Connecting the Neopixels to Lilypad
Step 8: Completing the circuit with the charge controller
Step 9: Finishing touches

Construction time: 4 hours

List of materials you will need

  1. 65 Mini Solar Panels
  2. 1-yard Neoprene fabric
  3. Nickel Battery Tabs
  4. Conductive Nylon Tape
  5. Solar Charger
  6. Lithium Ion Polymer Battery – 3.7v 1200mAh
  7. Lighter/see-through fabric (we used linen here)
  8. LilyPad or another sewable Microcontroller
  9. Conductive Thread
  10. 9 individually addressable LEDs (we used sewable Neopixels)
  11. 2-pin socket JST connector

Equipment needed: Laser cutter or possibly a Cricut, (we haven’t tested this as an alternative, but neoprene is listed on the Cricut website), or another programmable cutting machine.

Design of the necklace and circuit arrangement

This design uses solar panels to charge a lithium-ion battery, allowing us to power a Lilypad and neopixels even when we are not out in the sun. For a simpler design, consider powering something directly from solar panels! (For example, a vibration motor, or a speaker). Then you could skip the charge controller and battery, and you might need fewer panels.

Link to the laser-cut file for the necklace
  1. The top part of the necklace
  2. The bottom part of the necklace

In these files, we kept the panels very close together for aesthetic reasons but it did make the sewing and wiring more challenging. You may want to space your panels out a bit more. (Skim through the rest of the tutorial to see what we mean).

Now, let’s start making!

Step 1: Soldering the nickel strips

After testing several methods, we decided to solder nickel strips onto the back of our mini solar panels. This allows us to make good contact with a conductive tape circuit, and it will also allow us to secure the panels between two pieces of fabric, by sewing around the nickel strips (see below steps). 

Other methods we tried:

The first trial was an attempt at soldering the panels to copper tape (image on the top left). We quickly saw that this would not work very well because the panels popped off. It was also hard to align them into patterns.

The second trial consisted of soldering nickel battery tabs to the ends of the panels, which is the method demonstrated here (image on the bottom left). Fabric cover could be placed on either side of the tab and the panels could rest against a line of conductive tape. Sandwiching the panels between fabric and conductive tape meant we didn’t have to solder them to the circuit traces, which made it faster to assemble The lack of solder also makes it faster to assemble and more flexible.

Step 2: Laser cutting instructions

For the necklace material, we chose neoprene because it does not fray, and the thickness of the material created a window that is the perfect size for the solar panels. Keep note that the neoprene fabric has a different color on both sides, and here we used blue at the front with a yellow piece behind it.

The exact measurements and placement of the solar panels and the neopixels used here are provided in the link to the laser cut file. We used Adobe Illustrator to make the design of the necklace (65 windows for the solar panels, 9 eyeball designs for the neopixels) and used an Epilog Mini laser to cut the fabric.

Note: For ease of sewing we recommend you expand the space between the panels to 3/16” as opposed to the 1/16″ we have on the laser cut file which was a little tight.

Which materials should you use?

Neoprene, felt, or anything not woven, are the most appropriate materials for this project. Woven fabrics such as cotton, linen, and many polyesters, will fray when cut. Polyesters also tend to be derived from plastic which may not be safe for laser cutting and cause them to melt. We tested with felt at first, and while the cutting went great it proved to be thinner overall. The thickness of neoprene, caused by the foam layer, worked well for this application, so we highly recommend you use the same. Check with your maker space for what fabrics can be cut (usually, leather is also allowed).

Step 3: Laying out the wiring for the solar panel circuit with conductive tape

The logic of the tape circuit is to use two parallel pieces of tape (like a railroad track) to connect groupings of solar panels in parallel. The nickel tabs we soldered onto the solar panels will make contact with the conductive tape and a top piece of fabric (added last) will help keep them in place. 

The trickiest part of our layout is that we wanted to connect multiple groups of parallel panels in series. To do this, we connected a piece of conductive tape diagonally, from the top of one parallel grouping to the bottom of the next one. See diagrams and videos below.

To learn more about circuit connections you can check out our post on testing solar panels with a multimeter

As noted above, we decided to charge a battery from our solar panels, and we are using a charge controller to regulate that. The charge controller we used is looking for at least 6.5V, between 50mah and 1A, which is why we needed so many solar panels. If you choose to power something else, you might need fewer panels.

Tips: To be safe and avoid a short, use a small piece of electrical tape to provide some insulation.

In the next step, we will use a piece of fabric to pin the solar panels and tape connections in place.

Step 4: Sewing the panels in place

Once you are done with the arrangement in step 3, now it’s time to trap the panels in place so they won’t move once the necklace is on a body.

Working row-by-row we added a row of low-contrast stitching in between the nickel strips on each panel trapping the conductive tape and keeping the solar panels in place

The tutorial below shows how to prepare and sew the panels in place on a sample piece of the necklace. We used a white thread here for a clearer demonstration but you can use blue thread for better finishing.

Step 5: Testing the circuit output in the sun

In full exposure to the sun, the solar panels should output around 8 to 9 volts. Check with a multimeter.

Step 6: Sewing in the Neopixels

For the output, NeoPixels were hand sewn in with conductive thread, but only through half the fabric (not all the way through) with the conductive lines running through the top piece of the necklace.

Step 7: Connecting the Neopixels to Lilypad

The Neopixels were then connected to power, and ground on the top piece of the necklace and the data line on the bottom piece to make sure the data line did not touch the power line (to avoid shorting).

You can also use the newer versions of the Lilypad, or other sewable boards such as the Adafruit Circuit Playground or Flora. The power, GND, and data pins on these boards will allow for direct sewing lines without any overlap because they have more than one GND connection, which will make it easier to layout the circuit.

Step 8: Completing the circuit with the charge controller

On the charge controller, “batt” is the port for the battery, and “load” is where you plug whatever you would like to power, in our case, we plugged in a Lilypad. 

To connect the solar panels to the “DC in” port of the controller we used a barrel jack connector, and stripped the other side of it, connecting the raw wires directly to our conductive tape circuit.

Apologies for not documenting this part, but you may review the Solar Scarf tutorial for similar Hard/Soft connections between wires and conductive tape circuits.

Step 9: Finishing touches

Finally, the back half is sewn on. Lay the back (yellow) side of the top piece on the yellow side of the back panel and sew both pieces to each other.

Here is our finished solar necklace in action!

Did you try your own version? Let us know in the comments!

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