Intro: Slap Switch: Simple, No-Solder Touch Switch
The Slap Switch is a simple resistance touch switch, designed for my Explode the Controller project to incorporate physical play in computer games with the Makey Makey and Scratch. The project needed a touch switch that was:
- sturdy, to be slapped hard during active play without breaking
- small and light, to be mounted in many places and orientations
- durable, to survive repeat use in STEAM classroom projects
- scrap cardboard
- 2 colors of stranded wire (recommend 16 gauge or thicker)
- 2 stainless fender washers (1/4" inner diameter x 1-1/4" outer diameter)
- 2 sheet metal screws (30cm, round/pan head, head must be wider than 1/4")
- duct tape
- hot glue gun
- knife for cutting cardboard
- wire strippers
- large nail, awl, or needle for punching holes in cardboard
- multimeter for testing
Special thanks to Susan at the South End Technology Center in Boston for photographing this build!
Step 1: Cutting Cardboard
Cut your clean, scrap cardboard into 3-1/2" x 5" rectangles. You will need enough of these rectangles to build a stack that is thicker than the length of your sheet metal screws (see picture, usually 6-8 layers for a 2" screw).
Once you have cut enough rectangles, remove 2 layers from the stack and set the rest aside. Cut out a 2" x 3" rectangle from the center of each of the 2 layers removed.
You should now have 2 "cut out" layers and 4+ "solid" layers for your stack.
Step 2: Taping Layers
Stack the "solid" layers together and wrap them in tape (I usually use duct tape, but the masking tape pictured here works fine).
Stack the 2 "cut out" layers of cardboard, and connect them by wrapping in tape as pictured.
Step 3: Adding Hardware
Place the two washers in the center of the "solid" stack. Make sure there is a gap between the edges of the washers, 1/4" or so.
Mark the "solid" stack at the center of the hole in each washer.
With a large nail, awl, or needle, punch straight through all layers of the cardboard stack at each mark.
Replace the washers over the holes, and insert the screws. Tighten the screws with a screwdriver until the washers are secure, taking care not to over-tighten and strip the holes.
With a knife, clean off any tape sticking to the screw points where they came through the cardboard (the metal needs to be well exposed to make a solid connection with the wires).
Step 4: Gluing the Stack
Attach the "solid" and "cut out" stacks using the hot glue gun.
Make 2 cuts into, but not through, the bottom layer of cardboard on the "cut out" side. These will allow the wires space to run out from the screws without keeping the stack from sitting flush against a surface.
Step 5: Preparing the Wires (optional)
Students can be tough on circuit parts, and stranded connecting wires get frayed and snapped pretty quickly if they aren't reinforced. My solution is to make an exposed loop at the wire ends and have the kids connect them using alligator clips.
Start with a 24" piece of braided wire. 1" from the end of the wire, cut through the insulating sheath. Slide this cut insulation down, but not fully off, to expose a 1/2" section of the stranded wire.
Fold the wire back on itself to make an exposed loop in the wire, and hot glue the insulation together to hold it in place.
Wrap the cut end in tape to further secure it.
Do this 2 times.
Step 6: Attaching the Wires
NOTE: This build was designed for students who haven't learned soldering yet, but go for it if you know how :)
Select a length of wire, at least 24" long. Remove 1/2" of the sheath from one end.
Wrap the braided wire tightly into the exposed threads on one of the screw points coming through the bottom of the cardboard stack.
Tack the wire onto the cardboard an inch or so from the screw point, and double check that the wrapped end is still tight. Avoid gluing directly onto the connection, as this can be hard to troubleshoot if you miss.
Once you're satisfied with the connection to the screw, run the length of the wire out along one of the cuts you made in step 4, and tack it in place with hot glue.
Repeat with a second wire (of a different color?) on the other screw.
Step 7: Testing
Use a multimeter or a Makey Makey to test the your connections. If there's an issue, it's most likely the connection point where the wire wraps around the screw.
If it works, you're ready to play!