Introduction: Re-configurable Light-up No-Solder Matching Board

About: The mission of the K-12 Maker team is to help K-12 classroom educators create and deliver fun, enriching Maker experiences - no matter what subject they teach. Building upon our experiences as K-12 teachers, w…

This low-cost matching board project combines simple electronics with creative expression, and can be used to reinforce academic content in many ways. The electronics are powered by a 3V coin cell, which can power a buzzer or other low-current 3V device - we used LEDs and conductive thread on textiles. No soldering is required and all connections are made by wrapping or clipping wires or conductive thread.

We are Amy and Diane of the K12 team at the MIT Edgerton Center. Our group hosts STEM Outreach for visiting student groups, and Professional Development on student-centered Maker projects, Makerspaces, and innovative tools. All of our projects are designed to give students choice while developing skills with STEM/Maker concepts, tools, and materials.

The flags in this sample are made from felt and ribbons, inexpensive materials that do not require students to have al ot of experience with textiles or sewing. This makes it easy to create something that looks and you can be proud of. This board was set up as a matching game where each flag corresponded with a question, though it could also be set up for decoys and multiple solutions. Alligator clip jumpers on the back allow for easy reconfiguring.

In this Instructable, we’ll first show how to create the mounting board, followed by the electronic connections on the back of the board, then the creative content pieces, and finally pull it all together.


Cardboard, paper clips, paper fasteners (brass fold-back), index cards; LEDs (through-hole and E-textile), conductive thread, alligator clips, 3V coin cell battery (such as CR2032), flexible wire (22 AWG in this example), wire strippers, textiles (such as felt, fabric, ribbon), basic sewing tools (scissors, needle), embroidery floss

Step 1: Set Up the Board

Lay out a board (cardboard, cardstock, something stiff enough to stand or hang solidly), by setting out placeholders for the content and their mounting features. Mark the location of each flag with a number (1, 2, 3…) and the location of each index card with a letter (A, B, C…). This will help you build a key for the board's connections.

The flags will be held on by paper clips that also make electrical connections (+) and (-) to the LED circuit. Mark the ½” slits for those paper clips - our spacing is 3.5” on center. About ½” below them, mark dots for the brass paper fasteners - our spacing is 3” on center. The paper clips will make a connection between conductive thread loops on the flags and the legs of the brass paper fasteners, this spacing makes that easy.

The index cards with questions/ captions for the flags are also held on by paper clips (use 1 or 2 as needed). Near each index card, mark a dot for the brass fastener that users will touch with the wand (which we'll make in the next step) to select this question/ caption. Choose a spot that makes sense to you - on our example the brass fastener is centered above the index card. Our spacing is 4.5” on center, placing the paper clips at the very edges of the 3” x 5” index cards. Mark ½” slits for these paper clips.

Use a craft knife or scissors to cut the small slits. Place cardboard or a cutting mat under the board to protect the table.

For the brass fasteners, use a push pin to start the holes, then a pencil or pen point to enlarge them. Push the brass fastener through and spread the legs flat on the back so the fastener is secure.

To avoid lots of wiring errors, make notes on the back of the board. Mark both the (+) and (-) connection points for the flags. Also mark the numbers for the flags and the letters for the index cards (they are mirrored from the front).

Step 2: Make the Electrical Connections - Power Source

Start by making a 3V power source and "wand". Use a 3V coin cell battery (CR2032 or CR2025) with or without a holder. You’ll need about 18” of red and black hook-up wire - we used 22 AWG stranded wire.

One end of the red (+) wire is stripped and then twisted around one end of a paper clip, which is taped to a pen, pencil or other stick to create a simple wand with a conductive tip. The other end of the wire is electrically connected to the (+) side of the battery by either taping the wire right onto the battery surface or by threading it through the (+) tab on the holder and twisting tightly. If you are taping directly to the battery, stranded wire is best because you can spread out the strands and make good contact with the battery surface. The last step on the power source is to connect the black wire to the (-) side of the battery, once again either taping it directly to the battery surface, or threading it through the (-) tab on the holder and twisting tightly. Leave the other end of the black wire detached for now.

Make sure that the exposed wires don't touch each other or the opposite side of the battery, either of which would short circuit the battery. Not only would the circuit no longer work, but the battery would heat up and waste all of the energy stored in it.

Mount the battery (or holder) in place on the board (front or back, we chose the front). If you are using a holder, hot glue the holder to the board. If not, fasten the battery with tape or any other method that suits you.

Note: We chose a 3V coin cell battery (instead of 2 AA batteries, each of which are 1.5 V) because its low current capability eliminated the need for a current-limiting resistor. Quick explanation: red and yellow LEDs really only want 2V, and if they get 3V from 2 AA batteries they can pull a lot of current and burn out. Blue, green and white LEDs need the full 3V to light up, so over-current burnout is not often a problem. By using a low current power source, we don't have to worry about burning out devices whether they prefer 2V or 3V.

Step 3: Setup the Electrical Connections - Negative First

Before moving on, as this is a re-usable board, we should consider wiring options. Some connections will be permanent and others changeable. Alligator clips are a great option for quickly and temporarily connecting one conductor (brass paper fastener) to another, but alligator clips can fall off. A more permanent connection can be made by using lengths of wire with stripped ends. We use the permanent wiring for the negative connections, and the alligator clips for the positive connections.

Negative (-) Connections (stripped wire): Start with the black (-) wire coming from the battery on the front of the board. Run it from the front of the board around the edge to the back. The (-) ends of all the answer/ flag circuits need to be connected to the (-) end of the battery. However, if we run separate wires from the (-) side of the battery to each flag directly, we risk a lot of tangling and use a lot of wire. To neaten and simplify things, we'll link the (-) contact from the battery to the flag closest to the battery location. From this flag, we will run a wire to its neighbor, and from this (-) to the (-) on its neighbor, and so on, until you connect all (-) points in the 2 rows of flags (this is called daisy-chaining).

For wiring one (-) to another (-), measure the distance between the (-) contact of one flag to the next, add a 3 to 4 inches to the length, then cut. Remove about 1.5" of insulation off of each end (it's easiest to do both ends before attaching). Either stranded or solid 22 AWG wire works for this (stranded in this example). Loop the exposed metal part around the paper fastener "wings" on the backside of the board. To make a good mechanical AND electrical connection, do your best to make your twists snug so metal is touching metal.

Step 4: Now the Positive!

Decide which flags correspond to which cards with questions/captions. Make sure to arrange the flags differently than the index cards; placing them in different positions in the grid allows your "testers" to be challenged! It might be useful to write down the key, like 1-D, 2-B, 3-A, etc.

Positive (+) Connections (alligator clips): For each pair, use an alligator clip jumper to connect the brass fastener at the (+) of the flag to the brass fastener at the corresponding index card. Make sure the alligator clip "teeth" are "chomping" on the brass legs tightly to get a good electrical connection. Repeat this for each of the question/ answer pairs.

(In this image, the paper clips are already attached to the cardboard. These paper clips will not be part of the electric circuit - they are simply a method to hold the card/ flag in place - so this wiring can be done before the cards/ flags are attached.)

Your board is now wired for the correct answers! (Incorrect answers could be fun too, if the users are challenged to find them.)

Step 5: Create the Flags

Some flags are simple blocks of color while others have many details. The relative height and width also vary between countries, though most are close to 3 : 5. Feel free to take "artistic license", in other words, make something that is recognizable and simplify the details. Our American flag has 3 white LEDs to represent 50 stars - as long as they are on a blue background of an appropriate size, the flag is easy to recognize.

It's always a good idea to design on paper first, so before you start cutting textiles, sketch your flag on paper or an index card (the overall size in our example is 3” x 5”, same as an index card). Use markers or colored pencils to help visualize the final design. To get a sense of how much detail you need, start with a simple drawing and add details a bit at a time until you feel it is identifiable. Plan for no more than 5 LEDs, and mark their locations.

Note: LED colors are important because of the voltage they need to turn on. Yellow and red LEDs require ~2V, and will work together; blue, green, and white LEDs all require ~3V and will work together. In a combination of low and high voltage LEDs, only the low voltage LEDs turn on. For example, if you try to use red, white, and blue together, only the red will turn on. One way to get combinations of colors is to use all white LEDs and color them yourself with permanent markers.

Measure and cut felt pieces as the background color and supporting structure for each of the flags that are being used as answers. For this project we used a method called appliqué (stitching a small piece of fabric onto a larger one, usually in a shape) to create the color blocks and details.

Using the British flag as a sample, measure and cut bits of ribbon to create the "Union Jack". Once stapled or pinned in place, hand sew down the red center cross using red thread or embroidery floss and the whip stitch. Remove the pins or staples when the piece is sewn on. Once these bigger lengths are firmly attached, move on to appliquéing each of the eight, smaller blue triangles.

Sew each of the other flags starting with a background of felt, and appliquéing pieces of felt or ribbon as needed to represent the flag of a country involved in this treaty. For small details, embroider with thick thread or embroidery floss. You can add objects like buttons or beads by sewing them on. For decorative objects without holes to sew through, or if you are running out of time (!), use fabric glue to fasten the objects to the felt.

Step 6: Prepare the LEDs

Each flag will contain its own circuit that is ready to be powered by a 3V battery. The LEDs will be arranged in parallel to each other, so they will all receive the same voltage. See note in previous step about choosing LED colors that will work together well electrically.

The LEDs are attached mechanically and electrically to the flags by sewing them on with conductive thread. You can use inexpensive component LEDs (with 2 wire leads sticking out the bottom), or try flat e-textile LEDs that are available specifically for sewing projects (we've used Sparkfun's LEDs, but Adafruit carries their own variety). Either way, you'll need to pay attention to the polarity; the (+) end of the LED must be connected to the (+) side of the battery, and the (-) end of the LED to the (-) of the battery. In component LEDs, the negative lead (wire) is the shorter of the two and is also closest to a small flat edge on the LED collar. On e-textile LEDs, the terminals (holes with conductive surfaces) are marked (+) and (-).

E-textile LEDs do not require any preparation for sewing. For component LEDs, coil the leads to create (+) and (-) terminals. Once the leads are coiled, it will be very difficult to identify polarity, so coil or mark them differently. One way is to coil the (+) lead vertical (perpendicular to the surface), and coil the (-) lead flat to the surface. Another way is to use a permanent marker to color the leads. The standard is to identify positive as red, and negative as black; you can mark your LED clearly even if you only have one marker. In the closeup of the front of the American flag from our example you can faintly see what's left of the red marker on the (+) lead.

When the LEDs are complete, use the wand attached to the battery to check that the LEDs still work and that you are sure of the polarity.

Step 7: Create LED Circuits With Conductive Thread

Now you’ll use conductive thread to sew the LEDs onto the flag creating a parallel circuit [all the (+)s are daisy-chained together, and all the (-)s are daisy-chained together].

First, arrange the LEDs so that their negative (-) leads are one side and all the positive (+) leads are on the opposite side. The benefit of keeping them in a row or column is that it will be easier to make sure the (+) and (-) threads do not touch and create a short circuit. Check out the photo of the back of the American flag to see how we arranged the LEDs.

Sew each LED in place, tightly stitching over each coil from front to back at least 3 times. Do one more tight stitch in the fabric to secure the thread before you cut it. You should now be able to touch the wand to the thread on the back of the flag and see the LED light up on the front. Mark the (+) or (-) end on the back of the flag, perhaps with a dot of red or black marker.

Each flag needs one (+) and one (-) contact that will connect to the battery. We’ll use uncoated small paper clips sewn onto the back, as shown in the image. Mark these places on the back 3.5” apart, about ½ inch down from the top, (-) on the left, (+) on the right. Sew one end of each paper clip on with conductive thread, at least 3 tight stitches over the metal and into the fabric (here you can hide the stitches in the fabric if it is thick enough, so the thread does not show on the front). From here you can do one more tight stitch in the fabric and cut the thread, or move right on to the daisy chaining.

Connect the (-) paper clip to all of the (-) ends of the LEDs by doing a train of running stitches from one to the next. Make sure that this train of stitches makes good contact at each LED and the (-) paper clip. Do the same for the (+) paper clip and all the (+) ends of the LEDs, making sure that the running stitch trains do not cross each other and short out.

Now comes the moment of truth! Use the wand and the battery to check if the flag circuit works. Sometimes the LEDs vary in brightness a bit, and sometimes you have to jiggle them a bit to get a good electrical connection. If nothing lights up, start debugging. First strategy is to check individual LEDs with the battery. If they work individually then there is likely a problem connecting to the paper clips through the train of running stitches. If the individual LEDs do not light, there may be a short between the (+) and (-) in the running stitches, and you will need to cut it to isolate the LEDs and continue checking them individually. Hang in there, debugging can be slow!

Step 8: Put It All Together

Assemble each flag to the board, sliding the paper clips through the slits on the board, from the front. On the back of the boards, make sure that paper clip is squeezed over the folded back pieces of the brass fasteners so it can make connections to (+) and (-) on the battery.

Assemble the index cards to their places, simply holding them in place with 1 or 2 paper clips through the slits you made earlier.

Give it a try! Touch the conductive end of the wand to the brass fastener near one of the answers and see the corresponding flag light up. If nothing lights up, check your circuit and look for connections that have come loose. Places to look: the alligator clip connections, the wires wrapped around the brass fasteners, the connection to the paperclip on the wand, and the wires on the battery itself.

Once your group has finished with this topic, save the board! You can replace both the questions and the answers, and re-arrange the alligator clips to set up a brand new quiz!

Thanks for trying our Instructable!

We hope you had fun designing and sharing your Re-configurable Light-up No-Solder Matching board.

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