Introduction: Disc\Wafer Switch for Battery Operated Device

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One of my pet-peeves with electronic devices is when they do not come with an On/Off switch. In all my past situations I was able to add a switch in to the wiring of the device.

Well, this time I cannot access any wiring, at least not with enough room to cut, strip and solder in a switch. So I needed to figure out a way to add a switch. I know that often times, battery operated devices that come with batteries pre-installed will have a plastic or paper tab at one of the battery connection points. So this got me thinking if I could just somehow make that switchable. And with a little thought and tinkering I came up with this.

A piece of cardboard with metal duct tape on both side and wires connected to tape on each side of the piece of cardboard.

Please note that I needed this device to be switchable a day from now. When I have some time, I will head over to the electronic surplus store and see if I can find a PCB that I can make a disc out of. I also didn't have a hole punch this size, so I will also see if I can find a better way to cut the discs out.

This is my first time ever needing this and my first time making it, so there is plenty of room for improving the over design and build process.

Step 1: Create Your Cardboard and Metal Duct Tape Discs

Please see Step 6(Addendum) on how to create this disc using PCB material. I did this AFTER I wrote and published this Instructable, hence it is an addendum.Ultimately, this is probably what you would want to do, but making the disc from cardboard and metal duct tape might be cheaper and great for a proof-of-concept assembly.

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For this project, I am building this for a size C battery. I wanted to make the disc as close to the same diameter as the battery so it wouldn't move around withing the battery compartment. You may need to adjust the size of the discs to accommodate the battery you are working with.

I found it easiest to cut a piece of cardboard and tape down to a square just big enough for the quarter to fit in, then holding the quarter and the material together, trim it down. For the metal tape, I trim a slight bit more from it so that it was slightly smaller than the cardboard disc. I didn't want to chance the edges being too close and coming in to contact with each other.

Step 2: Connect Wires.

On my first attempt at this, I tried to solder the wires. I don't know if it was the tape, or what, but I could not get the solder to secure the wire and tape together. So I just took a small piece of the metal tape and put it over the wires. I didn't take a good photo of it, but I did put some electrical tape between the two wires where they come off the edge of the disc to give them some more security.

Step 3: Drill a Whole in the Battery Compartment.

From this point forward, your situation will most likely be completely different than mine. But the rest of this Instructable should give you everything you need to know to adapt this switch to your project.

If your battery compartment closes like this one, you will need to drill a whole for the wires to come through. Also, when choosing where to place this disc, be sure to use one of the battery contacts that has the spring in it. This will allow for the connection to adapt to the thickness of the disc.

Step 4: Cut Out Space to Mount the Switch.

I used a Dremel tool. I started making the space slightly smaller than the switch, then slowly worked my way out, test fitting the switch frequently. Once the switch was in place, I drilled to holes for the mounting screws.

Step 5: Finished.

This is what my device looks like now. This is an automated hand sanitizer dispenser. It is used by our dog rescue but only during weekend adoption events. I didn't want the thing to be left on between events, and as you can see, the battery compartment has screws holding it together. It would be a pain to have to open it up before and after each event to install or remove batteries.

Step 6: Addendum: Making the Disc With PCB.

So I just happened to need to run an errand today that just happened to take me by the electronics surplus store. "Yes dear, it was just coincidence that I was at the electronics surplus store today. And No!, it didn't take me 2 hours to buy a single piece of PCB material. That only took 5 minutes. The other 1 hour and 55 minutes was looking around at all the stuff they have". LOL

OK, so this would be my preferred method for creating the disc part..

1. Find some PCB material, preferably scrap since it is usually much cheaper to buy.(Pics 1 & 2)

2. I used tin snips to cut the piece down to the rough size of a quarter.

3. Use a file or Dremel tool to round the piece out. I used vice grips to hold the quarter and PCB together , the trimmed around the quarter to make the final disc.

4. Unlike the metal duct tape, this time I was able to solder the wires directly to the disc.

5. Instead of using electrical tape to keep the wires apart, I used heat shrink tubing.