Build a Simple Robotic Metal Detector (part three)

Building a BFO Metal Detector

This is part three of four in a series on how you can make a metal detecting sensor for your robot. If you have missed the previous article go here to view it:

Here is a list of parts that you will need to build your metal detector. For this project I am connecting the metal detector to an arduino programmable controller ($30.00 from RadioShack). If you want to build just a regular metal detector that just makes sound all you have to do is replace the arduino with an 8 ohm speaker. This is also a handy thing to keep in mind if you have to troubleshoot this device.

At this point you will be assembling the circuitry of the metal detector. You will need all of the following items from the parts list along with a robot to install your metal detector on when you have completed this series as this tutorial assumes that you already have a robot.
  • Parts list:
  • Any 9v battery
  • Small Gauge Copper Wire (J1, J2)
  • 2x 220uF 16v electrolytic capacitor (C11, C12)
  • 5x 0.01uF polyester capacitor (C6, C7, C8, C9, C10)
  • 0.1uF polyester capacitor (C1, C2, C3, C4, C5)
  • 10k 1/4 watt 5% resistor (R1, R2, R3, R4, R5, R9)
  • 2.2m 1/4 watt 5% resistor (R6)
  • 39k 1/4 watt 5% resistor (R7, R8)
  • 2N2222A transistors - almost any NPN transistor will work (Q1, Q2, Q3, Q4, Q5, Q6)
  • Arduino Uno
  • Basic Stuff: wire, solder, soldering iron
  • Search coil (I1)
  • Reference  ocilator (I2)
(Click on this image to view it larger)

Completing the circuit:
(Click any image to view it full screen)

Line up the parts with the corresponding symbol on the schematic.
All of the parts should line up as shown above and just follow the schematic to assemble everything.

connection points to larger parts.

Fully assembled circuit.


  1. I'm trying to do this project but I don't read circuit schematics very well. Can you post a clean picture of a completed board or a video of it connected to the arduino and working?

  2. Sure, I will try to get that information uploaded sometime between now and next weekend.

  3. Alright, new photos have been uploaded. Sorry about the wait. I since I only have one Arduino I was going to try to set everything up again to demonstrate it working but I cant disconnect the Arduino from the robot to have it in the pictures as I currently have it set up so I just labeled all the wires with where there suppose to connect to. Let me know if you need anything else.

  4. Anonymous4/23/2012

    what's the maximum range of detection?

  5. Anonymous4/23/2012

    and what I want to detect using this setup is a cube of 10cm

  6. The range of detection depends greatly on the design of the search coil. My search coil detected metal objects of different sizes between 5 and 7 inches away. It would be pretty easy to make a few different coils and test out which works best.

  7. Anonymous4/24/2012

    Thanks for ur help :)

    1. Thanks for this wonderful post.The information out here is very informative.

  8. Anonymous6/28/2012

    If i want to build just a regular metal detector what about 1 and 2 the arduino power what shall i do with them

  9. I should have made this more clear. The arduino power 1 and 2 do not correspond to the 1 and 2 that are labeled connect to arduino. Just ignore my plugs in the schematic. All you have to do is make sure that the arduino has power and then connect the positive wire(1) to a digital pin on the arduino. The negative wire (2) goes to GND.

  10. Anonymous6/28/2012

    Thanks for the info

    but here's what I get from what you've said and please correct me if I'm wrong that I just connect the end of the wires of "arduino power" to each other (nothing is connected between them)?

    and what if I want to connect a speaker and led with arduino connected can I'd just connect a speaker to one more pin and add the same code for it ?

    one last thing if I used 0.5 mm copper wire instead of 0.25 how would this affect the magnetic field of the wire?

    finally thanks again for you amazing work :)

  11. Almost, "arduino power" is just your regular arduino power supply. Those wires do not get connected together They go to a power jack on the arduino.

    I don't know about a speaker connected to the arduino but I tested this using a buzzer from Radio Shack ($2.19) and that worked perfectly and an LED could easily be added as well.

    Also thinner gauge wire works better but you should be fine using .5

    If you have any more questions let me know, I realize that these posts need some clarification and I will try editing them so that they are more coherent.

  12. Anonymous6/29/2012

    I think I didn't make the first question clear to you
    If I intend not to use arduino what should I do with this "arduino power" wires?

  13. Nothing, you can leave them off, don't connect them together either.

  14. Anonymous6/29/2012

    about j1 &j2 do i have to put a jumper or normal wire ?

  15. Thanks for sharing the nice post..

  16. Very nice but i think you should get a breadboard for xmas :D

    1. Understandable, this is an old project and I have been meaning to redo it.

  17. Anonymous3/07/2013

    is R6 2.2 milli ohms or 2.2 megha ohms

  18. madelin4/28/2014

    you can send me a scheme and more instruction to make a metal detector? please send to [email protected]