This Instructable details how to make a professional-grade (waterproof) tactical pressure switch for activating rifle-mounted lasers, scopes, TacLights, scopes, etc.
I found that quite frequently I accidentally left the laser on my red dot sight turned on. This led to more than one dead battery when I needed it most. With this remote pressure switch, the dot only turns on when I need it, instead of running down before it's necessary. It also adds a professional "look" to my paintball marker, adding to the "milsim" theme.
The principle of operation is quite simple. There are two conductive pieces of copper foil that are separated by a spongy foam, and when the foil is pressed together, they connect through a hole in the middle of the foam.
I was able to make this switch and wire it into my scope in under two hours, using only materials I had on hand. Granted, had I not been documenting the process, it probably would have taken an hour or less.
Also note that the accessory can be returned to its normal operating mode by simply removing the battery isolator, shorting the switch.
Step 1: Materials
Here are the parts you need:
+A scope/laser/light/etc of your choice
+An old car cell phone charger cord - If you prefer a curly cord, just like the commercial ones have, that is. Bonus points if the cable is colored black. An old telephone cable should work, too, but having a straight segment at the switch end makes life a lot easier. Also, you only need two wires to make the switch work.
+A small rectangle of plastic stock 1.5" x 0.5" - The rectangle will form the semi-rigid switch body. This can be anything from part of an old credit card to a cutout from a Chubs Wipes container. I used the latter.
+Heat shrink tubing - Black is best, as it doesn't stand out as much. You'll need at least 0.75" tubing to cover the switch itself and some smaller sizes to seal the cord end. I used a piece about 2" long and trimmed it once it was shrunk. This can be found anywhere from Fry's electronics (they have a great variety box) to Radio Shack.
+Light-duty epoxy to seal the seams between tubing segments (thanks Spork) or (in my case)
super glue, if nothing else is available. Note that if you will need the switch to be completely flexible, super glue will crack, allowing moisture inside the switch.
+Copper tape - Two strips of tape form the switch contacts. I used some leftover tape from shielding my bass guitar. Aluminum could be used, except that it doesn't solder. Any conductive, solder-able tape or foil will work.
+Thin packing foam - This is what keeps the switch off when there's no pressure on it. I used a leftover sheet of pink foam, the kind that is made of very small bubbles. Whatever you use, it has to be thick enough to hold the conductive tape apart but thick enough to not need too much force to activate.
+Small strip of paper - Depending on the model of scope/sight/laser/light you're using, it might be necessary to isolate the sides of the battery from the compartment. The idea is to only have the battery connected when the switch is pressed.
+Solder of your choice
Step 2: Tools
Here's what you need:
+Drill bit the diameter of the cord you're using
-PROTIP: Take care of your soldering iron tip! Mine is a mess. Always clean with a wet sponge after use, and when using ironclad tips, DO NOT GRIND THEM DOWN!
+Hair dryer (not shown) to shrink the tubing
Step 3: Making the Switch Body and Contact Surfaces
With the plastic stock in hand, cut a small notch on one end that's the width of the wire being used. You will probably need the pliers to pull the notch out out. The wire will be super glued in place later on.
Now cut a 1" long rectangle of copper tape that will fit on the plastic stock with just a bit folded over the sides to hold it in place. Make sure you leave about 0.25" of exposed plastic on either end of the stock. Before putting the tape in place, it would be a good idea to place a tiny drop of super glue on the plastic first, just to make sure it doesn't move.
To make the other contact, cut a piece of copper tape the same size as the first. If it has a wax paper backing, simply peel it off and re-apply it flipped over so the tape will stick to the paper. We'll work with this contact soon.
Step 4: Soldering the Wire to the Contacts
Take your sacrificial phone charger and cut however long a segment of cord you need. I suggest using the straight end (if yours has one) for the switch. Strip the insulation off the cord on both ends, and then off each wire. If your cord has more than two wires, you can snip the others off. You won't be needing them.
As a rule of thumb, tin the exposed ends of each wire. In this case though, I would not recommend twisting the strands of the switch-end wires, and if possible, fan them out just slightly. This should help make a flatter, stronger contact with the tape.
Position the cord so the end of the insulation is just at the end of the slot in the switch body. Now solder one wire to the copper tape on the body, and the other wire to the loose piece of contact tape. Make sure that both pieces of tape are lined up.
Now would be a good time to place a bead of super glue in the notch and hold the cord in place until it cures.
Step 5: Making the Contact Insulator
Next cut a rectangle of foam exactly the size of the plastic stock. Make sure to snip out the wire slot just as on the body. It is critical that the foam be the same size as the body, as it will be insulating the switch contacts until the switch is activated. If it's not just the right size, the switch might get stuck "on" once the heat-shrink tubing is applied.
Make a small rectangular (or circular) hole in the middle of the foam so that the copper plates will make contact when pressed together. Hook up your multimeter to the other end of the cord and test for conductivity when pressed. You might need to put a bead of solder on one piece tape to help bridge the gap.
If you find that the switch needs too much force to activate, try gluing small squares of plastic (or material of your choice) to the center of the top piece of foil. This should make it easier. Again, start with a short piece and work your way up until you find something that works.
Connect it to a multimeter and hold it against, say, a screwdriver to get a feel for how much pressure is needed to turn on. Adjust it as necessary, because this is the last chance to test the switch before sealing it up for good.
Step 6: Shrinking the Tubing
With the switch tested and working, it's time to encase it in heat-shrink tubing.
Find the length and size of tubing you'll need for the switch body. It needs to be large enough that the switch isn't stuck closed before even shrinking it. Leave adequate spacing on both ends to account for shrinkage.
Use a hair dryer (or method of your choice) to shrink the tubing. I would not recommend the method I used
, which involved rubbing the soldering iron over the tubing.
Once the tubing has been shrunk to its limit, the flat end can be sealed with a drop of
superglue epoxy and pressure. Simply apply a drop to the edge, and capillary action should suck the glue in. Then place the flat end under a heavy book, etc. for a few minutes. Once cured, snip the excess tubing off. Make sure not to cut too close, so as to keep a good sealed end.
With the cord end of the switch tubing shrunk, slip 2-3 successively smaller <0.5" long segments of tubing down the cord. Start with the largest and finish once the tubing has created a seal around the cord. Then
superglue epoxy the seams so as to ensure a watertight seal.
Step 7: Preparing the Scope for the Switch
Step 8: Wiring the Switch Into the Scope
With the cap drilled, strip and tin the switch wires with solder. Stick the cord through the hole and line up the wires where they will go. One end should connect to the battery terminal, and the other should connect to the scope circuit. In my case, red goes to scope, white to battery.
Before trying to solder the wire to the "finger" bit, tin a spot with solder. This makes life much easier when soldering the wire in place.
With the scope circuit end done, now it's time for the battery contact. Cut a small circle of copper tape and solder the remaining wire to the middle of the tape. Stick the tape in the center of the cap so that it will be guaranteed contact with the battery.
The only problem now is isolating the battery. If your compartment is conductive all around the battery, you will need a small strip of paper to insulate it. Cut the strip wide enough so that it can fold down over the battery and keep the "fingers" from coming in contact with it.
PRO TIP: It's easiest to place the paper in the compartment BEFORE sliding the battery in.
Lastly, put a drop or two of
superglue epoxy where the cord meets the battery cap to ensure waterproofing.
Step 9: Testing the Switch
With the cap done, screw it onto the scope and turn it on. There shouldn't be any light or laser dot until you press the pressure switch. If there is, go back and make sure the "fingers" aren't touching the battery and the paper is correctly isolating it.
Step 10: Finished!
If everything is working fine, congratulations! You are now the proud owner of a tactical pressure switch. You can make one for every one of your rifle attachments and activate them without ever moving your away from the trigger. Hopefully you'll get some extra bragging rights and some increased battery life, to boot.
As an added bonus, use Velcro cable straps to attach the cord and switch to the gun body. This will keep the cord from getting snagged on anything.
Remember that to bypass the switch and use your rifle accessory normally, simply short out the switch by removing the battery isolator strip.
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