Finishing your sensor at home

 Didn't quite finish your senor in class? Here are the instructions on how to finish up and have a working security alarm!

You'll likely need a wrench and a pair of needle nose pliers to make the job go a little easier. You'll need some tape as well. Almost any tape will work, we used electrical tape in class.

Students found two new componets in their box this week. A long yellow wire with the ends stripped off and a long orange wire connected to a battery pack. Set these aside, we'll use them in a moment.

Just about everybody got this far last week. The clothing pin should have two bolts in it with the heads of the bolts on the inside of the clothing pin.

Start with your yellow wire. Take one of the exposed metal ends and wrap it in a loop around one of the bolts.

Once it is in place, screw the nut on to hold the wire in place.

This can be a little tough especially if you have small hands. Use the wrench and pliers to make the job easier. If you can do it without taking the clothing pin apart then your life will be easier later. Squeezing clothing pin back together can be a little annoying. BUT taking them apart will make this step easier and won't harm the project in the long run.

Alright, one side of the clothing pin should now have a yellow wire secured to it. We're now going to do the exact same thing to the other side of the clothing pin with the orange wire. The orange wire has a short end and a long end. You want to connect the SHORT end to the clothing pin. This will sit the battery pack near the clothing pin and the LED will be futher away.

Alright, almost there. Squeeze your clothing pin back into one piece. The flat heads of the bolts should be touching. Time to grab your LED.





Grab the long lose ends of wire and your LED. LEDs are polar, which mean they will only let electricity flow in one direction. Test your LED and make sure it lights up. If it doesn't, flip it over. Learn more about LEDs here.

Flip your LED over. Technically it can be in any position as long as the correct ends are connected to the correct wires. But in my experience this is the easiest way to handle the LED.

Twist the loose end of one of the wires to the end of the LED like a twisty tie. In the picture you can see a small peice of tape holding the yellow and orange wire together. Not a necessity but it makes handeling a little easier.

Cut a short piece of electrical tape and wrap it around the electrical connection we just made. Some kids in class used masking tape because it is a little easier to tear and manipulate. 

Alright, we're almost there! Twist and wrap the other side the exact same way. IMPORTANT  Use TWO pieces of tape here. It may be tempting to twist both ends and wrap one big piece of tape around but if you do it will likely cause a SHORT CIRCUIT and your LED will not work. 

Your LED should now be lit. When you open the clothing pin the light should go out. Students received a small piece of plastic with a hole in it. If you want to recreate this project or you tiny hacker misplaced the piece a plastic tab from a bread bad will work well. Tie a piece of string the the plastic tab and the other end to something you want to monitor. Place the tab in between the clothing pins. Id the object you are monitoring moves, the tab will be pulled out and the LED will light up!


Sensors and hardware hacks

In class we started working with the concept of a sensor and circuits. We started working with ways to make a DIY security alarm. The video below is very similar to what we will be doing, but instead of a motor, the alarm will cause a LED to light up.

Liked making invisible ink in class? The UV reactive ink is an example of chemical encryption. It's easy and cheap to make so you never have to run out.

It's made out of tonic water and trace quantities of highlighter ink. Tonic water contains quinine, a chemical that is fluorescent.


Nothing special about this tonic water, any bottle will do it.

Nothing special about this tonic water, any bottle will do it.

There's quinine in there but it's too diluted. We're going to boil most of the water off and be left with sugar and quinine.

Pour about half of a quart sized bottle of tonic water in a microwave safe bowl or a sauce pan if you're doing it on the stove top. You'll also need an adults help. The trick is to go slow. If you boil the water off too fast, the sugar will caramelize and leave you with a useless stick mess. Microwave it for about 5 minutes at a time. By the time you're done you'll be left with about 1/10th your original volume of liquid. About half a quart (500 ml) will boil down to about 3 tablespoons (50 ml). You'll know you're close to being done when the tonic water starts to thicken and look just a tiny bit brown.

If you have a larger UV light, conrats! You are done. If you're using the UV LED from class then we have to do just a little bit more work. The LED doesn't put out enough light to get the tonic water to really shine on it's own, so we're going to add another fluorescent element to give it some umph. 

Highlighter ink is another fluorescent molecule. We're going to add just a tiny bit. Too much and the ink looks yellow-y. Too little and the ink will be hard to read. So crack open a highlighter and stick a wooden coffee stir stick into the ink reserve.  Then mix it in with your tonic water goo. Go slow and check it with your UV light as you go. 

It really doesn't take much of this stuff.

It really doesn't take much of this stuff.

If your ink is a little thick, add a few drops of regular tonic water. It should be thicker than water alone but you should still be able to paint it on with a paint brush. If the ink is too thick, it will dry clear but shiny. If you dilute it enough, it will be very, very difficult to see with out the UV light once it dries. Consider doing this step in a room with low light so you can see the fluorescence easier.  Besides that, your all done. Have fun.

I've seen instructions on how to make UV ink using just highlighters. I tried it out and it was pretty fun. It seems to work well on skin but is still pretty visible on white paper. Try it out, what do you think?

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