How to Build Your Own Metal Detector? Step-By-Step Guide

Hello to all of the electronic enthusiasts and DIY lovers out there! The following article is made to simplify the basics of electronics. In it, you will find a walk-through guide of how to build your own metal detector.

Keep in mind that this tool will not have the same ability as a commercial metal detector- for example finding hidden gold beneath the Earth's surface. You could install complicated circuits to your, self-made metal detector; to make it perfect.

However, that's not the point of this article. As I said, this is just a guide to practice your abilities and get yourself familiar with the basics of electronics.

A lot of people have high expectations, so I don’t want to get anyone disappointed with the results.

The focus should be on improving your skills; or if you are new to the whole world of electronics, on learning where and how to start.

In the guide, you will find steps that include explanations of how to make the circuit on a breadboard, as well as on a perfboard; the materials you will need and how to troubleshoot a problem.

Creating the circuit

Firstly, you would need a blueprint for making a circuit and a diagram of the breadboard. A quick Google search should do the trick! Once you’ve found the diagram go through the next steps; since it can prove difficult to properly follow the instructions if you are not equipped with a schematic. In the next steps try to follow the diagram as much as possible.

Sometimes the first circuit that you create can fail to work; so, the general advice is to try to create it on a breadboard, before moving on to a perfboard.

Here is the list of the materials you will need in order to make a circuit on a breadboard:

  • A breadboard.
  • IC Chip (555 Timer).
  • 9V Clip and Battery.
  • uF electrolytic capacitors- 2x1 and 1x10.
  • A cylinder with a 1-inch diameter.
  • 47 KΩ Resistor.
  • Jumper wires.
  • 28 AWG Wire.
  • A speaker.
  • Alligator clips.

Make sure to coil the wire around the cylinder approximately 220 to 250 times. You should also leave 2 to 2,5 inches of wire on both sides of the coil. Once you’ve done that it’s time to take your breadboard!

Connection Time

This part may sound a bit confusing, but If you do it properly your circuit should work, and you can move to the perfboard later on. The IC Chip you equipped, should be placed in the middle of the breadboard.

You can see the pins around your IC Chip; when it’s notch is facing the left, the pins on the bottom are in numerical order from 1 to 4 (from left to right). The order continues on the top- the pins should be from 5 to 8 (from the top left to the top right).

Concerning the connections, pins 4 and 2 should be connected to pins 8 and 6, with a jumper.

So, pin 4 is connected to 8, while pin 2 is connected to 6. The next thing you should connect to pin 2 is a 1 uF electrolytic capacitor. Make sure you also connect the capacitor to ground. Now, the thing that you should connect to the ground is pin 1, using a jumper wire.

Take a look at your 10 uF electrolytic capacitor; you should see that one side has a + on it. That side should be connected to pin 3 of the IC. Now, take the negative side (marked with a -) of your 10 uF electrolytic capacitor and connect it to the speaker; while making sure that the other connection of the speaker is to ground.

Using a jumper wire, connect the Positive Power rail to pin 4; also, the pin 6 of the IC with the 47K ohm resistor. Now, connect the other end of the 47K ohm resistor with the jumper from pin 3. Going back to pin 6 of the IC, you should connect it to a 1 uF electrolytic capacitor Finally, connect the breadboard power rails to the battery slip leads (the broad power rails, are on the side, making two long rows).

Now, it’s time to make the thing that detects metal. Take a cylindrical, nonmetal, hollow object (for example a plastic bottle* with a diameter of 1 inch; and a magnet wire. You should tape the wire to the bottle, and it around 240 times; leaving 2 inches in the end.

Tape the end of the coil, making sure you have 2 inches left in the end. Now, you should have a wired bottle, with 2 inches of coil left from each side. It’s important to scrape off the insulation at the end of the wire with a sharp object. You mustn’t forget this step since without doing it the circuit won’t work!

One more step left, and your circuit is complete. Connect the alligator clips from the wire to the positive end of the 1 uF capacitor and to the 47 K resistor. Finally, connect the battery clip to 9V battery- if you've done everything right, the circuit will make a high-pitched sound! You can test this by putting a metal object inside the wired bottle; if you succeeded, the pitch of the sound will change. Bravo, this means you are done!

Creating a permanent circuit

The list of items you need, for making a permanent circuit, is almost the same as the one used to make a circuit for a breadboard. However, some of the items differ, so let’s go over them again:

  • A Perfboard.
  • IC Chip (555 Timer).
  • 9V Clip and Battery.
  • uF electrolytic capacitors- 2x1 and 1x10.
  • A cylinder with a 1-inch diameter.
  • 47 KΩ Resistor.
  • IC socket with 8 pins
  • 28 AWG Wire.
  • A speaker.
  • A switch

The first thing we’ll focus on is making an inductor. As you probably know by now, inductors are made from a bunch of wires. The goal is to coil them in a way that they can resist changes in current.

The inductance of the indicator can depend on many things. For example, the number of turns you made on the coil, the diameter of the coil, its height and width and the materials inside the coil. So, if you change any of these factors the inductance will change.

With the inductor we’ll make this time, you should be able to detect metal by hovering over it.

If you already have an inductor you can use it; however, you can also follow this guide, and make a new one- the choice is up to you.

Again, you’ll need a hollow, cylindrical object made out of plastic. Tape the wire to it, and coil it approximately 150 times around the cylinder; make sure you leave around 2 inches of wire on both ends.

With a sharp object remove insulation from the ends (you can use lighter or scissors). Once you’ve completed this step, take your perfboard and place the IC socket in the middle.

The next few steps are completely the same as the ones we went over before; simply place the components as you did on the breadboard. Once you’ve made all of the connections solder them.

It’s time to attach the wires to the board; then solder them to the switch. You should solder two more wires to the wires from the coil, and you are done. Now insert the 555timer IC into its socket; apply tape or hot glue to the leads in order to secure them.

To lower the chances of circuit shortage, also apply hot glue/tape over the soldered joints. It’s time to find a base to place the circuit on. You can use a craft stick or be a bit more creative - it’s your metal detector, so you can design this part based on your preferences.

Once you’ve attached the battery to the clips, you need to make sure that the circuit is organized in a presentable manner. You can use just about anything around the house for that; the only requirement is that no metals are near the coil once you've attached the base. Congratulations, you are done!

Troubleshooting

Finishing this project, but not being able to start your metal detector, sure feels awful. Unfortunately, problems occur, and it can even happen to the best of us. If you start building your metal detector while tired; you may need to have a couple of breaks before finishing. Most of the mistakes occur if you are not fully concentrated. Since the process of making electronic devices requires you to be very precise, you needn’t rush it. Don’t skim through the guide, or try to wing it, because you can end up unsatisfied with the results. In case you did follow everything and still can’t get this device to work this part should help you out a bit!

Problem 1: You can’t get your circuit to work.

As frustrating as this can be, there is a myriad of reasons why this problem can occur.

In case you didn’t make the connections properly, take a look at your schematic. This can often be the cause of your problem, so make sure you connected everything as drawn.

If you are sure you’ve connected everything, and still can’t get your circuit to work; the problem may be with the soldering bridges. This means that you made more than one connection by solder. This is a very common mistake. Again, look at your scheme and the guidelines we provided. If this seems to be the root of your problem, you may need to start again; since you probably secured soldered joints with the hot glue. The good news is that if you do start over, you will know exactly what the problem was, and you can fix it easily.

However, if you think you’ve completed this step without any mistakes, check if you inserted the capacitor correctly. Maybe you inserted the wrong polarity, don’t stress - you can just use a multimeter to check. With this device you can see the continuity of each capacitor; and if you see that there is continuity between the poles, you need to replace the capacitor. The reason for this is that due to the wrong polarity the capacitor broke down. Each capacitor has a breaking voltage and once it reaches it, it will break down.

Problem 2: Your circuit produces noise, but the pitch stays the same.

The best thing to do when faced with this issue is to change the number of turns in the coil, or its size. Also, make sure you made the connection with the inductor.

Problem 3: Everything works, except the speaker, produces a high-pitched noise

If this is the case, there is a problem with capacitors. The solution is to discharge the capacitor. Using pillars, connect the ends of the capacitor with a metal. Make sure to turn off the circuit before using pillars. The capacitor needs some time to cool down. So, leave your capacitor to rest a bit, and it will be ready to be used again. In case this problem occurs more than twice, you should change the capacitance of your capacitor.

Conclusion

In case you faced some problems, troubleshooting tips should help you clear them up. This is not a simple project especially for beginners on “how to build your own metal detector”. The important thing to remember is that you shouldn’t beat yourself up if you made some mistakes. Making mistakes is an essential part of learning, so don’t stress about them. Always try to improve yourself, and learn from your mistakes. Whatever the results may be, don’t give up on creating and enjoy projects ahead!

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