Make a Metal Detector

Hello everyone!! Today I am going to show you how to make a simple metal detector. Can you find gold hidden under the ground with this metal detector? Answer is NO. DO NOT EXPECT THIS METAL DETECTOR TO WORK LIKE COMMERCIAL METAL DETECTORS. You could make Metal Detectors with complicated circuits to perfectly accomplish the job. But that is not point of this build, in fact the main point of the build is to familiarize with the basics of simple electronics. Just leaving this as a warning, because a lot of people raise their expectations too high to be disappointed too much with anything I make or show. Also I am an 11th grader, not a Graduate in electronics major, so I am bound to make mistakes, and I would definitely be happy if you help me correct them. Anyway now that the warnings are laid forth, let's keep moving.

The circuit is build based on the instructions provided by a youtuber named Ludic Science. Pay him a visit for more info, or more interesting circuits.

The instructable is divided into many steps to make sure it is super simple to follow. The steps are divided in the following order:

1) Step 1: Watch Video!

2) Step 2: Circuit schematic & breadboard diagram.

3) Step 3-9: Making the circuit on a breadboard.

4) Step 11-16: Making the circuit on a perfboard.

5) Step 17: How does it work?

6) Step 18 & 19: Troubleshooting tips and finishing words.

Alright, lets get to the build!!

Most of the things in the video is covered in this instructable, but if you prefer watching videos over reading instruction then watch my video! I desperately hope it will be helpful to you in some way. Also watching the video on youtube will increase my youtube views and maybe my funds for my future projects, so give it a go!

So here's the schematic and the breadboard diagram of the circuit. I hope it could be a great aid in making the circuit, because it is really difficult to individually instruct on where to connect the wires. So try to follow the schematic and the breadboard diagram if you can.

Often times the circuit that we try to create ends up failing to work, so it is always recommended to create any circuit on a breadboard before soldering on a perfboard.

To make it on a breadboard you will need:

1) 555 Timer IC Chip.

2) 2 X 1 uF electrolytic capacitors.

3)1 X 10 uF electrolytic capacitor.

4) 47 KΩ Resistor.

5) A speaker

6) 9V Battery & Clip

7) Breadboard

8) 28 AWG Wire & a cylinder with a diameter of 1 inch.

Take the cylinder, coil the wire 220-250 times around it. Make sure to leave about 2 inches of wire on each end of the coil. (I will describe it in details later on if it is confusing.)

9) Jumper wires & Alligator clips.

And you'd also need a lot of patience to coil the wires without messing up.

First take the breadboard.

Place the IC Chip in the middle of the board as shown in the picture. Make sure the notch on the IC is facing the left. When the notch of the IC is facing the left, then the pins on the bottom left to bottom right are 1,2,3,4 and the pins on the top right to top left are 5,6,7,8. Refer to the picture for the pinout.

Connect pin 4 and pin 8 of the IC using a jumper.

Connect pin 2 and pin 6 of the IC using a jumper.

Connect an 1 uF electrolytic capacitor to ground and pin 2 of the IC.

Connect pin 1 of the IC to Ground using a jumper wire.

Connect the + side of an 10 uF electrolytic capacitor to pin 3 of the IC.

Connect the speaker to ground and negative end of the 10 uF capacitor we connected just now.

Connect pin 4 of the IC to Positive Power rail using a jumper wire.

Connect the 47K ohm resistor to pin 6 of the IC.

Connect a jumper from Pin 3 of the IC to the other end of the 47K ohm resistor.

Connect an 1 uF electrolytic capacitor to pin 6 of the IC.

Connect the battery clip leads to the breadboard power rails (the two long rows on the side.)

So now we will be making the most important part of the circuit, the thing that will detect the metal.

Take a cylindrical bottle of plastic with a diameter of 1 inch. It is really important that the cylindrical object be plastic or something nonmetal and hollow.

Take some magnet wire. Magnet wire is just regular copper wire with a thin layer of enamel insulation. Leave 2 inches of wire in the end, and tape the wire to the bottle. Now start coiling the wire around the bottle 220-250 times. Try to make the coil neat and clean. Then tape the end of the coil to the bottle so that you have 2 inches of wire left on the end again. So now you have a coil of wire around a bottle and the ends of the coil are two inches long.

Now take a scissor and scrape off the insulation from the end of the wire. This step is EXTREMELY IMPORTANT. If you want you could also burn it off using a lighter. If you skip this step, the wires won't make any contact with the alligator clips, and the circuit won't work.

Now attach the alligator clips from the wire to 47 K resistor and the + end of the 1 uF electrolytic capacitor.

The circuit is done!! Take a 9 Volt battery and connect it to the battery clip. The circuit should create an annoyingly loud high pitched noise.

Now bring a metal such as scissors or pliers inside the bottle with the coil, and the pitch of the sound should change indicating you have a metal inside the bottle! If you put your fingers or any other dense non metal objects, the pitch of the noise wouldn't change. It would only change if a metal is brought close to it. Congratulations! You are halfway done! Now time to make it permanent!!!

To make the circuit permanent you will need the following things:

1) 555 Timer IC Chip.

2) 2 X 1 uF electrolytic capacitors.

3)1 X 10 uF electrolytic capacitor.

4) 47 KΩ Resistor.

5) A speaker

6) 9V Battery&Clip

7) 28 AWG Wire.

8) Perfboard.

9) Switch

10) A cylindrical object with diameter of 1.5 inches.

11) 8 pin IC socket. (Soldering an IC will damage the IC due to the heat. So instead we will solder the socket, and later on insert the IC into the socket.)

Once again we are going to make the inductor. If you want you could use the inductor from last time, but I decided to change it. I decided to make the coil flatter and bigger in diameter, so now you could detect metal by just hovering the coil on top of a metal.

So take the plastic cylindrical object, and tape the wire to the cylinder leaving two inches of wire in the end, and then start coiling 150 times around the plastic cylinder. Leaving two inches of wire on the end again tape the wire in place. Remove insulation from the ends of the wire using lighter or scissor.

Place the IC socket in the middle of the perfboard. Imagining it is the IC chip from before, place the components around it like you did before on the breadboard. Refer to the schematic to create the circuit again. The images I provided of the circuit may be misleading at stages because a lot of the connections I did were while soldering, rather than through placing wires and jumpers. So refer to the schematic as much as you can.

Solder the connections you created so far.

Use safety precautions while soldering.

Now attach two long wires to board and solder them to the switch. Attach two more wires and solder them to the wires from the coil. You circuit is done!

Now that you are done with the soldering, insert the 555 timer IC into the socket.

Now apply hot glue or use tape to cover the leads and soldering joints to reduce chances of shorting the circuit.

Choose something to place the circuit on. I chose a craftstick because that was the easiest base for me to find. But you should be a bit more creative than me, at least to respect the hardwork you put in to create this circuit.

And attach the battery to the clips. Now using rubber bands, hot glue and whatever you have in your house, organize the circuit in a presentable fashion, making sure there are no metals near the coil when you attach the base.

We are finally DONE!!! Just press the switch and it should turn on the annoyingly high pitch sound, and bring a metal close by and you will hear the change in pitch of the noise. Congratulations! But if it didn't work, don't worry, I have some troubleshooting tips for you.

I am no expert, and by no means am I qualified to explain how it works. But I could relay the basic concept to you if you are beginning to learn about electronics like me. If you find any mistakes in my explanation help me correct it.

Inductors: Inductors are just a bunch of wires coiled in way that it resists any change in current. The inductance of the inductor depends on the diameter of the coil, number of turns on the coil, the height and width of the coil, and the material that is inside the coil (hollow air or metal rod etc.). If any of the above mentioned factors are changed the inductance would change.

A 555 timer chip can do a lot of things, but most commonly it is used to create a clocking signal. Pin 3 of the IC is the output pin. It can Output a high or low voltage. The sound is created when the output of Pin 3 changes from High to Low really fast. The speed of changing of the output from high to low is what creates the pitch of the noise. If the output changes slower then the speaker would have a low pitch noise, and if the output changes fast the speaker would create a high pitch noise.

Pin 2 and 6 connect to two comparators inside. What the comparators does is that it compares the input voltages to output either a high or a low. The output of Pin 2 and 6 then determines the output of the pin 3. The two 1 uf Capacitors and resistor and the inductor are wired in a way so that the input voltage of Pin 2 and 6 keeps changing, and if the input voltage of pin 2 and 6 keeps changing their outputs would keep changing, and the output of pin 3 would keep changing. It's like a chain of reaction. If the values of any of the resistor, or 1 uF capacitors or the inductor is changed, the output frequency of Pin 3 would changed . In our case the value of the capacitor and resistor stays constant. However the value of the inductor can be changed.

When we bring a metal close to the coil, the inductance of the coil increases. The change in inductance in turn leads to a series of other events that would take a professional to explain. But anyway when the inductance changes the end result is that the pitch of the noise changes.

A higher inductance on the coil= Lower pitch noise.

A lower inductance on the coil= Higher Pitch noise.

This is probably the worst explanation you have read about the functions of a circuit, but that is the best I can do before confusing you and possibly even myself.

So in the next few paragraphs I will try to solve a few of the problems you might be facing while making it.

Problem 1: MY CIRCUIT DOESN"T WORK YOU LIAR! YOUR ENTIRE LIFE IS A LIE!

Solution: Calm down because I don't have either the patience or the sadistic nature in me to make someone waste hours of their youth to make a fake circuit. Let's slow down and get along with the rest of the problems. ( This happened to me countless times on youtube, people blaming me for their circuit not working.)

Problem 2: The Circuit doesn't work, would you help me fix it? I can't even hear a sound.

Solution: Now this is a better way to express your opinions and needs. Alright the circuit may not be working due to several reason. Did you make your connections properly according to the schematic? Check it. If the connections are right, check whether you made soldering bridges. (accidentally connecting more than one connection by solder overflow). Did you insert the capacitor of proper polarity? Check with a multimeter to see the continuity of each capacitor, if there is continuity between the poles of one of the capacitors, then that capacitor needs to be replaced, since the capacitor broke down upon reaching the Breaking Voltage. Did you properly remove the insulation from the ends of the coil? Because a lot of times people don't do it and magically their circuit doesn't work. Did you insert the chip in the right orientation? Check to make sure the notch is facing the left if you are using the breadboard diagram to build it. Try changing the speaker if you want.

Problem 3: My circuit produces noise, but the pitch doesn't change when I bring a metal close to the coil!

Check the connection with the inductor. Did you make it too small?? Try changing the size and number of turns in the coil.

Problem 4: My circuit works, and also changes pitch when a metal comes nearby. But after a bit of use, the speaker creates a really high and cranky pitched noise!

Solution: It's a problem with the capacitors. Turn off the circuit and using pliers hold a metal and connect the two ends of the capacitor with it. It should discharge the capacitor. Let the capacitor cool down for a bit and it should be ready to be used again. If this keeps happening frequently change the capacitance of the capacitor.

Problem 5: My circuit changes pitch without any need for anything!

Solution: May the lord be on your side to help you out through tough times. Amen.

I hope you guys found this circuit interesting and maybe want to try recreate it too. If so, then my writing this instructable was successful. Once again I am an amateur in electronics, and definitely could make mistakes. I would appreciate anyone fixing the mistakes for me. Help me improve the explanation of how this circuit works if you can. Thank you for reading and hope you have a good day!