The VoltPen (Highlighter Into Voltmeter)

In this instructable I will show you how to make the VoltPen, a very easy, cheap and practical voltmeter!

First I would like to explain the positives and the limitations of this VoltPen.

PRO's :
-It doesn't need a battery as it is powered from the source where you are reading voltage from.
-Very small to carry everywhere.
-It can prick through wires without damaging them.
-Extremely cheap to make. ( I spent around £3 on this project)
-Very easy to make.
-It looks cool!

Limitations:
-It will not read AC voltage.
-It will not read bellow 2.5V (the minimum voltage for it to work).
-It will not read more than 30V.
-The tip is very sharp so you need to be careful not to poke yourself when the cap is not on.(You can use a dull point if children are going to use it)

Although this project is very easy to make, I took lots of photos so you can see the whole process.
Lets start...
 

First of all, here is a list of materials and tools I used for this project.
(Don't worry if you don't have some of the tools I used. Most of them can be replaced with everyday items around the home)

Materials

-Highlighter (I used two to make sure I have a good looking finish. You can use only one, but you may damage the casing a bit while removing the front part of the highlighter.)
-2.5-30V DC voltmeter, ebay Link
-Alligator clamp wire
-Masking tape
-Pin

If you want to add a reverse polarity warning led, you will need as well:

-Drill and a 6mm drill bit
-Gloves
-LED (I used a Red 5mm LED)
-LED panel holder
-1K resistor (I tested mine from 2.5v to 24v and this resistor seems to work fine, although I would not leave it on for a long time at more than 12v.)

Tools

-Digital Caliper ( Any ruler will do the job)
-Dremel and bits
-Hot glue gun
-Quick Clamp
-Solder

The first thing we need to do is get the highlighter ready. 

In the photos you can see that I've used two highlighters to make sure the finished product looks good. For the head I used a highlighter that I had around the house with little life left. 

For the body I used a highlighter that I did like for this project as It has a rubber grip that makes it looks like a tool already.
I used some gloves to avoid getting my hand stained.

Once both highlighters are cut, I used the dremel with a pointy bit to retouch them until the head and the body of the highlighter join easily. 

I didn't want to waste a brand new highlighter, so I fit the internal bit from the new highlighter to the old one and taped the head to  the body of the highlighter. I also cut the cap so it would fit. ( see picture)

Place some masking tape where you want to fit the voltmeter.

Measure the Voltmeter and mark the hole accordingly.
You don't need to do this if you trust the measurements on the ebay listing. I just wanted to make the hole as tight as possible.

Cut the hole with the dremel. Try to fit the voltmeter inside the hole. If it doesn't fit, retouch with a small bit on the dremel until you can fit the voltmeter snuggly.

With the dremel make a hole for the wire. Take one of the alligator clamps off the cable and feed the cable through the hole you made on the end of the highlighter. 

Now is a good moment to erase the writing on the highlighter. Before removing the writing I protected the rubber grip of the highlighter so it will not be damaged. I used an eraser and a bit of acetone (nail polish remover) to get rid of the writing on one side. I left the other side untouched.

Fit the voltmeter through the highlighter and place it in position. With the help of a small screw driver carefully push it into the hole. Be careful not to damage any of the electronic components on the back of the voltmeter.

Apply hot glue to the inside of the highlighter. You can help it a bit with a pencil or something to push the glue down. Make sure the voltmeter is level with the highlighter's surface outside, hold it in position until the glue hardens.

With a drill bit of 6mm drill a hole for the LED holder. 

Here is a schematic of the wiring. As you can see it's very simple, all you have to do is solder the negative side of the voltmeter to the alligator clamp and the positive side to the tip. To connect the polarity warning led, all you have to do is solder the anode to the negative and the cathode to the positive through the 1K resistor.

Remove the tip and cut it in half. 

Insert the pin through the tip. Fit the red wire through the hole in the head of the highlighter and solder it to the tip. 
Replace the tip and bend the pin on the inside, so once it is glued it will not go anywhere.

Once you have done this, glue the body to the head of the highlighter and use a quick clamp to hold it while it dries.

Well done! you've finished. Enjoy using this tool. Since I made mine, I don't use my multimeter as often, as sometimes all I need to check is the voltage.

Here are some pictures of other VoltPens I have made.

Thank you for reading my Instructable. Please check my other Instructables for cool projects like this.