Magical Magnetism: Intro to Reed Switches (Normally Closed)

Written by: Jill Dawson

Lift to Light!

In this tutorial, we will demonstrate key differences between two types of reed switches and teach you how to make a piece of interactive art, an electrified “cobweb” card, that lights up when it’s lifted.

normally closed reed switch project
reed switch cobweb card

Introduction

In our first reed switch tutorial, Magical Magnetism: Intro to Reed Switches (Normally Open), we introduced the most common type of reed switch, demonstrated how to use one in a circuit, and explained how to make a magnetic wand that can trigger any circuit you make with one.

In this tutorial, we’ll be continuing our exploration of magnetic switches by introducing you to a less common type of reed switch (“normally closed”) that has a slightly different look and functionality. We will also show you how to apply this type of switch in an electrified version of a Victorian Era valentine that works a bit like a refrigerator door, only lighting up when it’s open.

normally closed reed switch circuit

What is a reed switch?

A reed switch is a small electrical component containing two thin fibers, or reeds, that are highly susceptible to magnetization. Reed switches respond to the presence and absence of a magnetic field

What is the most common type of reed switch?

The most common type of reed switch is called a “normally open,” or NO reed switch.

What are the properties of the most common type of reed switch?

In the most common type of reed switch, called a “normally open” reed switch, thin contacts encased inside usually contain an open gap between them, as illustrated in the diagram below.

When part of a circuit, this open gap prevents electricity from flowing through the switch unless a magnet is placed nearby.  

While some reed switches are made of glass, this one is insulated with plastic.
When there is a gap between the contacts inside of a reed switch, current cannot flow through it.

How does a magnet impact the most common type of reed switch?

If a magnet is within range of a “normally open” reed switch, the force of its magnetic field causes the reeds inside to move closer together until they touch, closing the opening and forming a connection that allows electricity to flow through it.  When this happens, and the circuit closes, you’ll notice some sort of actuation in the circuit, such as the lighting of an LED, the turning of a motor, or even the sound of a buzzer!

When the magnet is pulled away from the “normally open” reed switch, the reeds move apart again, recreating the gap that was there before. With the switch now open, the flow of electricity within the circuit is once again disrupted.

The animation above, depicting a “normally open” reed switch coming in contact with a magnet, is copyrighted material. It is being used here in accordance with Educational Fair Use (Source).  

A Reed Switch With a Bump

Unlike the “normally open” reed switch, which normally does not allow current to flow through it (unless a magnet is near enough to close it), a reed switch that is “normally closed,” reacts in an opposite manner (with help from an extra, smaller magnet hidden inside).

The animation above, depicting a “normally closed” reed switch and biasing magnet, coming in contact with a stronger magnet, is copyrighted material attributed to Dr. Steven R. Stuve, Ph.D.  It is being used here in accordance with Educational Fair Use. 
Source:  docstuve.com.  

The reeds inside of a “normally closed” reed switch are normally pulled closed with help from a tiny magnet contained inside of the switch enclosure. In addition to holding the reeds inside of the switch in a closed position, the inclusion of this magnet inside of the switch also causes the “normally closed” reed switch to have a visible bump. The presence of a bump is useful for telling the two reed switches apart, but it can be more fiddly than its counterpart in paper circuit applications.

Normally Open
Normally Closed (Bumpy)
normally open reed switch
A “normally open” reed switch is smooth and may have small dots on its most magnetic side.
normally closed reed switch
A “normally closed” reed switch has a bump concealing a small biasing magnet inside.

The gap inside of a “normally open” reed switch CLOSES when a magnet is nearby, completing the circuit and causing the LED to switch on.

A magnet nearby turns the LED on.

The gap inside a “normally closed” reed switch OPENS when a magnet is nearby, interrupting the circuit and causing the LED to switch off.

A magnet nearby turns the LED off.

Normally Open
Normally Closed (Bumpy)
normally open reed switch circuit
A magnet nearby turns the LED on.
normally closed reed switch circuit
A magnet nearby (touching in this case) turns the LED off.

Tips, Tricks & Call-outs
For details on building this circuit using our Paper Switch Template, please visit Magical Magnetism: Intro to Reed Switches (Normally Open). The process for integrating a “normally closed” reed switch is identical. While curling the leads of a “normally closed” reed switch is not required (see the right-most image above), it can increase stability, making it easier to line up the magnet in a paper circuit where precision is required. A demonstration of this technique may be found later in this tutorial.

One example of a circuit using a “normally open” reed switch is a magnetic wand bringing an illustration to life as it hovers above it.

One example of a circuit using a “normally closed” reed switch is a refrigerator that only lights up when the door is open.

Normally Open
Normally Closed (Bumpy)
Normally Open Reed Switch Template Bigger Magnet SQUARE
A more powerful magnet can be further away and have the same effect.
Normally Closed reed switch with medium ceramic magnet
A more powerful magnet can be further away and have the same effect, but it’s placement may be more fiddly.

What’s a Cobweb?

To demonstrate how you might apply a “normally closed” reed switch to a paper circuit project, we will be showing you how to construct a modernized version of a design, called a “cobweb,” that has been around for hundreds of years.

Cobwebs—also known as beehives, flower cages, or birdcages—are a rare example of a mechanical or movable valentine consisting of a minimum of two layers of paper. First, a web or cage would be cut from a piece of paper by making a pattern of concentric circles, leaving attachment points at regular intervals. In the center of the spiral, a delicate thread would be attached and its outer edges would be pasted directly on top of a second sheet on which an image or message would be written, painted, or printed.

Nancy Rosin, Cataloger at the Met Museum’s Department of Drawings and Prints

Our project, an electrified cobweb card, will feature four layers: a paper cage, artwork, a circuit, and a backing sheet.

cobweb card with reed switch

Materials & Tools

Circuit Sticker mega pack
1 or more Circuit Sticker LEDs
conductive tapes
conductive fabric or copper tape
battery holder & battery
paper battery holder & coin battery
normally closed reed switch & magnet
1 reed switch (normally closed) & magnet
needle & thread
needle & thread
text weight paper for card
4 pieces of copy paper (5×5 in)
cardstock for card
1 piece of cardstock (6×6 in)
protractor lid circular objects
a protractor or circular object
scissors ruler pencil
sharp scissors, ruler, & pencil
scotch tape
Scotch tape
glue double sided tape
craft glue or double sided tape
layers of cobweb card
your own artwork

Directions

Build the Top Layer

Step 1: Fold

Traditionally, the top layer of a cobweb card was intricately cut by hand while the paper was flat. In interest of time, we will be folding ours to achieve a similar effect.

To get started fold one of the 5″ x 5″ sheets of paper into quarters diagonally to create a triangle. Open that triangle up with its long edge facing away from you. Then fold the right and left sides down parallel with the center to create a diamond. Fold the resulting diamond in half and crease the hinge.

folding GIF
Fold.

Step 2: Plan Your Cuts

Starting from top of the diamond you just folded (the closed end), use a pencil to mark several evenly spaced lines, stopping within 1/2″ from the bottom.

Start the mark for your last cut about 1/2″ from the bottom of your diamond

The bend of your lines will determine the shape of your cobweb/ paper cage. If you prefer a rounded top layer, tracing the curve of a protractor, or a circular object laying around your house, is helpful. If you prefer a paper cage with more angles, your lines may be drawn straight across.

Marking gif
Plan your cuts.

Step 3: Alternate Your Cuts

Begin making your first cut from the top open side (not the hinged side) of your paper diamond, stopping before you get completely to the edge. Then, start your second cut from the hinged side, stopping before you get completely to the opposite edge. Continue making alternating cuts, stopping short of the edges, until you’ve only got about 1/2″ or so of uncut paper remaining at the bottom of your diamond.

cutting gif
Alternate your cuts.

Step 4: Unfold

Starting at the top, open edge of your paper diamond, carefully unfold your cobweb and press it flat. Leaving it pressed under a heavy book for a while will help minimize the folds.

unfolding gif
Unfold.

Step 5: Reinforce & Thread the Center

To help prevent tearing, apply a small square of Scotch tape to the center of your cobweb layer as reinforcement. Make sure that the tape does not overlap any of the cuts you made, or the cobweb won’t open properly. Then, starting on the outside of your cobweb, use a needle to pull a piece of thread or thin cord through the center of the cobweb and back around to the outer side. Pull the tails of your thread through so that they are even. Then gently test your design by holding the paper down with one hand and pulling the threads up with the other.

threading gif
Reinforce and thread the center.

If you are unhappy with the results of your first attempt, repeat steps 1-5 with a second piece of 5″ X 5″ paper. If you are satisfied, proceed to the next step.

Build the Circuit Layer

Step 1: Consider the Battery

Decide whether you wish be able to access and/or replace your battery. If battery access is not important, you can adhere the battery onto the circuit layer of your project without using a battery holder. (You may view an example of this method in the gallery below) .

If battery access is important, however, you will need to assemble and use a paper battery holder, which you’ll be placing on the back side of your card. Battery Template (PDF)

Tips, Tricks & Call-outs
If you are unsure how to assemble a paper battery holder, please visit the Paper Battery Holder Tutorial. Using Conductive Fabric Tape, rather than copper tape, is preferable for this project.

Step 2: Plan & Create Your Circuit

You will be placing your art layer on top of the circuit layer in order to light up an element of your choice; but, you’ll first need to ensure that you leave enough room in your circuit design to accommodate the “normally closed” reed switch in the center of the circuit layer.   Because we will be placing the magnet somewhere in the center of our cobweb layer, the reed switch needs to be located near the center of the circuit.

In the images below, I’m using a copy of my artwork layer to plan and build the circuit. I folded it diagonally to locate the center and used double sided tape to adhere it to the 6″ X 6″ backing layer).

Next, I penciled in the location of a Circuit Sticker LED and sketched the positive trace.

circuit layer
Pencil the location for your LED and positive lead.
circuit layer
Place the reed switch in the center of your artwork.

I then sketched the negative trace, leaving a gap in the center for the reed switch. Because I was using a paper battery holder to allow access to the battery, I adhered it to the back side of the backing layer and brought the battery leads around to the front of circuit layer.

normally closed reed switch circuit layer
The circuit includes a gap for the switch in the center .
normally closed reed switch circuit layer
The battery holder has been attached to the back side.

The pictures below show the location of the battery holder and its leads wrapping around to the front side of the circuit layer. I used Conductive Fabric Tape to construct the battery holder and the circuit.

battery on back of paper circuit
The battery holder has been attached to the back of the backing layer with a piece of Scotch tape.
normally closed reed switch circuit layer
The battery leads have been brought around to the front of the circuit layer.

After laying down the positive and negative traces of the circuit, I turned my “normally closed” reed switch with the bump facing upward and used my fingers to gently curve the metal legs on each end to help add stability.

bending legs of reed switch gif
While not required, bending the legs of your “normally closed” reed switch can improve its stability.
normally closed reed switch circuit layer
I used Conductive Fabric Tape for the circuit leads.
normally closed reed switch circuit layer
While not required, I gently curved the legs of the reed switch with my fingers.

Next, I added the LED and adhered the legs of the reed switch with small pieces of Conductive Fabric Tape.

normally closed reed switch circuit layer
Add the Circuit Sticker LED & test the reed switch.
normally closed reed switch circuit layer
Tape down the curved legs of the reed switch.

Once the second leg of the “normally closed” reed switch was taped down, the circuit was complete and CLOSED, allowing the LED(s) to turn on.

normally closed reed switch circuit layer
At this point, it’s helpful to hold your art layer over the circuit layer to ensure that your LED is properly aligned.
normally closed reed switch circuit
You can use more than one LED.

When I placed the magnet on top of the switch to determine its polarity and placement, the switch OPENED and the LED(s) turned off.

With the magnet in place (and the switch turned off), I adhered a small piece of double sided tape on top of it to help with the next step of getting the magnet in the correct place inside of the top layer.

normally closed reed switch circuit layer
With the magnet in place on top of the “normally closed” reed switch, the circuit is OPEN and the LED is OFF.

Step 3: Add the Magnet to the Cobweb

After ensuring that the LED is in the correct location to light up your artwork layer, it’s time to place the magnet on the cobweb layer.

Start by placing the cobweb directly on top of the circuit layer with the string side up, and the sides aligned, and press the center down until it comes into contact with the taped magnet.

The LED should remain OFF when the cobweb layer is in place over the magnet.

Lift up the cobweb layer and flip it over to the side where the magnet should now be. Add a small piece of Scotch tape directly on top of the magnet to keep it in place.

Carefully place the cobweb layer on top of the circuit layer with the string side up.
two layers of cobweb project
Add a small piece of Scotch tape over the magnet to secure it to the cobweb layer.

Assemble the Layers

Once you’ve got the magnet in place on the back side of your cobweb layer, you need to tape or glue the art layer directly on top of the circuit layer.

This is the artwork layer.
I poked holes for the light to shine through & added a piece of vellum before sticking it on top the circuit layer.

After the artwork is in place, tape or glue the edges of the cobweb layer to the top of the art layer.

If everything is properly aligned, the LED should only light up when the cobweb hiding the magnet is lifted.

two layers of cobweb project
alien cobweb card open
normally closed reed switch example
This cobweb has a lot of fine, round cuts, so it lifts up higher.
normally closed reed switch gif
This cobweb has fewer cuts, with more space between them.

Gallery 2

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