Introduction: Magnet Activated LED Critter Scarf

This scarf uses a simple reed switch circuit so that the scarf's eyes light up when the head is snapped to the tail. Because the switch is in the head and the magnet is in the tail, multiple critters can be snapped together in single file to make a sort of animal based light display - this could be an idea for a class project where everyone makes their own one to take home, but they trigger each other as a group project.

The pattern is very basic so there is room to customise your critter - variants have included fox, stoat, lizard.

Conductive knitting yarn is used here as it all the components are close to each other and it will be easier to sew for beginners than conductive thread. Polar fleece can be cut without fraying, so less stitching is needed in the project. The circuit design is based around the 3D printed sewable battery holder Instructable.

Step 1: Materials and Tools


Download printable PDF pattern and circuit template below

About a meter of conductive yarn

a piece of heavy polar fleece about 100 x 10 mm

Some sewing thread to match the polar fleece

1 x sewable coins cell battery holder

1 x CR2032 coin cell battery

2 x LEDs

1 x reed switch

1x pair of snaps (or velcro dots if sewing these on will be too much challenge!)

Plastic canvas to cut the base for the circuit

1 x neodymium magnet (we used a 10 x 1.5 mm coin magnet)



A needle with a big eye

Needle nose pliers

Wire cutters

2 x coloured Sharpies

Step 2: Cutting and Marking the Plastic Canvas

Place the plastic canvas over the printout of the placement diagram. Draw around the outline of the triangle base with one colour, then the pink circuit traces with another. There should be 3 separate traces. Cut out the triangle base with scissors.

Step 3: Prepping the LEDs and Reed Switch for Sewing

With a Sharpie mark the top of the long positive leg of each of the LEDs. This is so we can tell which is positive after we bend the legs for stitching. The reed switch has no polarity (+ or - direction) so no need there.

Bend the legs of each LED at right angles so that the LED plastic base will sit flat on the base. Like they are doing the splits.

With the pliers, curl up a leg (see photo) so that you get a loop that can be easily sewn around. Do this to the other LED legs and also the reed switch leads.

Step 4: Stitching the Components and Canvas Together With Conductive Yarn

Lay out the battery holder, LEDs and reed switch on the canvas so each terminal on a component lines up with the traces. It is sometimes helpful to use a small piece of double sided tape to hold everything in place for sewing. look at the notes on the 1st photo above to see which parts are positive and negative.

Using the photos above as a guide, start with stitching the negative terminal of the battery holder to the canvas as you would a button hole, going around the hole and canvas 3 times. Make sure the stitching is tight rather than loose to get good connections. Continue stitching along the marked trace until you get to where the 1st LED leg goes (it will be negative) and stitch around the loop 3 times as you did with the battery holder. Continue stitching along trace until where the 2nd LED leg goes, stitch around the loop 3 times.

Fasten off, by threading the needle back through 2 or 3 of the last stitches on the back of the canvas and pulling thread through. Cut off the end. A dab of fast drying glue like superglue can help stop any fraying or unravelling.

Tie a knot in the thread again, and start the 2nd trace by stitching around the positive loop of the last LED you stitched around as you did with the last 2 loops. Keep stitching until you get to the 2nd positive LED loop, and stitch around it 3 times, then continue along trace until where the terminal loop of the reed switch starts and stitch around it 3 times. Fasten off as before.

Have a look at the back to make sure you there are no loose ends. And everything looks neat.

Now the 3rd and final trace! Re-attach thread to the other end of the reed switch and stitch around it 3 times to attach to the canvas. Now stitch along the marked trace line until you reach the positive battery holder hole, stitch around 3 times and fasten off as before.

Step 5: Testing the Circuit and Troubleshooting

Test the battery on a spare LED to make sure it light up. if it doesn't, flip it. If it still doesn't work, try a fresh battery.

Push the battery into the holder (+) side up. Nothing will light up yet it's OK though! Hold the magnet next to the reed switch this should activate it and LEDs will light up! Still nothing?

Things to look for:

There are 3 separate traces (the pink lines) that are basically our wires on the circuit. These need to be separate from each other, they are joined only by the components (LEDs, reed switch, battery holder) in the circuit. That is why we fasten off at the end of stitching a trace, and reattach thread at the beginning of a new one. If you stitched all together in one long path then everything would short circuit.

Make sure all knots/ends are tidy and not hanging, this could lead to shorting also.

Make sure all stitching is tightly wound around the loops on the components

The positive copper tape lead in the battery holder may have been flattened so both terminals are touching the negative side of the battery. Make sure the positive lead inside the holder is vertical, so it touches the positive part of the battery.

Step 6: Stitch the Snout Pocket to the Body

Thread a sewing needle with cotton thread. Take the "undersnout" piece and place it against the snout end of the long body piece. Sew around the edge to make a pocket.

Turn this pocket inside out so there is a nice finish for the head of your scarf. Insert the circuit you made into the pocket to see if it fits.

Step 7: Install the Snout Circuit

Place the snout circuit in the pocket with the LEDs facing towards the top layer of the scarf.

Using wire cutters or sharp point scissors snip a tiny slit just over where the LEDs sit in the pocket. Push the LEDs through the holes you have made.

Test the circuit by placing a magnet over the nose to light up the LEDs.

Step 8: Stitch the Magnet Into the Tail End

Place the magnet near the edge of the tail end of the scarf, making sure it is on the underside. Fold the edge over, and sew around the magnet so that it is trapped between the 2 pieces of fabric.

The magnet in the picture is a craft magnet but small neodymium magnets are stronger and more effective at activating the reed switch. Magnets need to be enclosed in this project because they are very dangerous if eaten. Well not 1 on it's own so much but if you swallow 2...

Step 9: Attach the Tail and Snaps

With cotton thread sew the tail to the underside of the scarf, just over the magnet is good.

If making a fox, take the white triangle piece and glue or sew it to the top side of the tail end.

Attach one half of the snaps sewing with needle and thread to the top layer of the scarf just above the magnet.

Position the head above the magnet until it lights up, and then work out where the other half of the snap goes under the snout. Sew into place.

Note: Sewing the snaps on may need some skill, if this is too much then you can use adhesive velcro dots as the fastener, just make sure they are positioned so that when joined they are in the right place that the magnet can activate the reed switch and light up.

Step 10: Sew on Ears. Test Scarf. Wear Scarf.

Sew on the ears - for a neat finish position them facing down and stitch, then fold up again.

Put the scarf on around your neck and join the snap or velcro, see the eyes light up! If you are making this as part of a class, each critter can activate another by fastening each head onto the tail of another. Make a light up animal chain.

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