Introduction: Velleman K7102 Metal Detector Kit

About: I am electronics engineer. Currently working in the High voltage direct current field. There is no better feeling than making something. And if you run in to some problems in the project, after trouble shootin…

Despite the fact, that i graduated as electronics engineer... time passed and i found my self using soldering iron, only to fix broken gadgets rather than to make my own. But when scrolling online i found this kit, i decided to revive my passion. And although given instructions are so clear that you do not even need this instructable, i decided to make fun upload maybe to inspire you to make something. First things first. What you will need.


Velleman K7102 kit (i got mine for 10$ in local electronics shop)


9V battery

buzzer(optional since it does not come with the kit)


Soldering iron( i suget picking up something like this if you are planning to get more seriuos about it but do not want to spend the big bucks upfront

Flush cut pliers

Helping hands (had them, although did not use do to my strange preference today)

tiny flat head screw driver( for adjusting the pot)

Step 1: Making Coils

There is no magic in this. Just winding provided wire around ferrite core as much turns as the manual suggests. One thing to make you life easier- make stoppers with zip ties. Constraining space where windings are, helps not to cluster all over the place. And after you are done just put some clear tape on top to keep everything tidy.

Step 2: Diode

Lets start putting components in place and soldering them. Since components come lined up in the order, Diode is first to be installed. 1N4148 to be precise. Just don't forget that polarity is important. Match the stripe on diode with the stripe on pcb. Bend the leads to keep it in place and solder it. And here comes the handy dandy flush cut pliers. Shorten those leads. :)

Step 3: Zenerdiode

No this is not the creepy uncle of the diode. But non the less they are similar in more ways than one, but the one you are interested is the polarity again. Mach the stripe is the name of the game :) And once again solder and trim the leads.

Step 4: Resistors

Resistance is quite difficult one to understand if you are not familiar with the electronics. It seems so angry and uncooperative. But hey, if you need to, you need to :D Put them in. You can check the values with multimeter, or resistor color code table. But i just put my fate in the assembly line, that it sorted them in needed order (engineer at it's finest) and shoved them in from R1 to R5. Bam solder, cut, be happy.

Step 5: Capasitors

Finally, step with some room for experimentation. Although, experimentation will come afterwards. But non the less for the first capacitor, designers gave you options. For now on choose whichever you want, later you will switch them if it does not work as you like. Thinking about how you will determine that? By the power of magical phrase of " why the f it is not detecting any metal". Oh yes, with all that joy of choice dont forget to put and solder the other, lonely one :D

Step 6: Transistors

Oh the transistor. Our three legged dog like friend. Come to think of it, it is nothing like a dog. With base emitter and collector it sounds more like a radio station quarters. But you have three of the transistors which are waiting to be soldered in. By the way, they all are identical. It is so nice to have things which are the same, for example thee one hundred bills, right? Jesus, i get distracted quite fast. Put them in, solder and cut the leads.

Step 7: LED

Say hello to the more attractive and popular friend of lonely diode. When people see diode, they ignore it, when people see light emitting diode- they get excited... I am guilty myself of committing such crime agains components> Don't judge me, LED glows, its pure magic :) Once again install, solder and trim... but wait, it its polar sensitive, like all the "celebrities" it requires to be put in the right place the right way. So... positive to positive, negative to negative. Simple yet overlooked more often than it should be...

Step 8: Potentiometers

Another component with siblings which are less impressive in this project. Potentiometer is like a resistor, but with more depth, has much more than you can notice at first. Yep it has range :D So install it, although there is correct way, you are not likely to put it in wrong, so chill. Everything is good on our beloved earth.

Step 9: Push Button

Ever wondered, what drives us to press the button which has a sticker or note besides it with "do not push"... yup.. curiosity always gets us :) so Put the button in, solder and be done with it. Do not worry, only one way it goes in again.

Step 10: Assembly

Connect the battery terminal to the point marked “+” (red) and “-” (black). Ever wondered why there is postive and negative? Why it is negative, how does it influence is badly? Like do we tend to curse more? Or be bad? But all jokes aside, do not be a funny one, and just for laughs connect it in reverse. Not that you are going to damage it in this case, but it is just not going to do anything. So save yourself some time. Do it right.

Connect the windings to their respective points marked with a, b, (L1) and c, d (L2). All jokes aside, don't forget to clean the tips of the windings from lacquer. Soldering something in, which has no contact to the rest of the board is pointless :D

Step 11: Test & Final Adjustments

1. Connect a 9V battery to the battery holder. (i guess you already have, and not just waiting for step 2)

2. Go to a place where NO metal object is known to be in the vicinity. (good luck, since pcb it self contains metal items :D)

3. Turn preset RV1 fully clockwise. (To the right to the right... from some song i guess)

4. Turn RV2 fully anti-clockwise. ( to the left to the left... it worked out)

5. Depress the push button and hold it in during the final adjustments. (Can i search for gold now?)

6. Turn RV1 anti-clockwise until the LED goes out. (Do not panic, it is not burned or permanently gone out)

So time to reflect. You can install the buzzer which is less sensitive than led. It is fun project that will take form 15 minutes to half hour, depending on your speed. It works, and is cheap, although gold finding missions are not likely to be carried out with this device. Fun little project to get familiar with electronics. Instructions are more than clear. And step by step are one of the best i have seen anywhere. Enjoy :) By the way, from schematic that it is above, you can make it your self for cheap. most of the parts i guess you will have already if you are in to electronics. Cheers