Cardboard Knife Switch

We're huge fans of knife switches. Besides being very sci-fi / horror film in style, as educators we find them to be the perfect way to explain the difference between and "open" and "closed" circuit and how a switch completes a circuit and allows electricity to flow.

You can obviously purchase a knife switch, but most of the affordable ones made today use cheap plastic for the base, not like the old ceramic models of yesteryear. And hey, if you're gonna go cheap, why not just use cardboard!?

We've created a simple template that will allow you to create your own knife switch using cardboard, some conductive tape, and a few brass fasteners.

Please Note! Knife switches are not used for most modern day circuits as they have been replaced by switches that are safer at high voltages, but since we’ll be working with low voltage circuits this DIY cardboard knife switch is perfect!

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Brown Dog Gadgets does in fact sell kits and supplies, but you don't need to buy anything from us to make this project. Though if you do it does help support us in creating new projects and teacher resources.

We've supplied a template so you can cut out the pieces using some cardboard. (You can use a craft knife, razor blade, scissors, or a laser cutter - whatever you have available!

You will need:

• 1 x Piece of Scrap Cardboard (Approx 8.5" x 11")
• 1 x Roll Conductive Tape (We used Maker Tape)
• 3 x Brass Fasteners

Use the template to cut out the four pieces you'll need.

You can print the template on paper then attach with glue or tape to a piece of cardboard to use as a guide for cutting. We used an X-ACTO knife to get nice clean cuts, but you can use whatever you have available that will cut cardboard.

There's also a vector file Cardboard Knife Switch Laser.pdf included that will work well for a laser cutter. If you want to cut cardboard with precision and speed, nothing beats a laser cutter!

Note the score lines on the front and back pieces. Those indicate where we need to fold the cardboard at 90 degree angles to create the base.

Once you have the cardboard pieces cut you'll need to add the tape.

We're using Maker Tape, which is a strong nylon-based tape that is conductive on both side and all the way through. Even the adhesive is conductive. (You can try to use copper foil tape, but it can be a pain to work with and is only conductive on one side, so you'll need to do some creative folding and overlapping.)

Once you have the tape in place, fold the front and back pieces as shown.

Note: The tape will need to go over the top of the front piece and down a bit to make proper contact with the lever.

Use the brass fasteners to assemble the switch as shown.

If your cardboard lever doesn't swing down into place easily you can pinch and bend the front and back pieces where the lever makes contact. Cardboard is nice and bendable!

You can test your switch using a multimeter or a simple circuit. Just connect to the left and right side of the base where the tape is. You can use alligator clips or more conductive tape. If you prefer to use wires, just tape them down using small pieces of conductive tape.

Note: The cardboard knife switch is meant for low-voltage DC circuits only!

If you have any issue with getting a good connection you may need to add a little more tape around the lever where it makes contact with the front piece. Just wrap a bit more tape around it so you get a nice tight friction fit.

Building this switch is a great activity for a classroom or workshop, as it's a quick and easy build requiring very few materials.

And remember, the Knife Switch is loved by mad scientists around the world!