Let's Make Robots!

TB-007 Metal Detector

TB-007 (ThunderBird 7) Big Brother of TB-6. (Blogged)

TB-007 is able to Detect Metal  (Coins, Rings, Gold, Electric Underground/Floor Cables and annoying Bottle Tops)

Improved Traction Design - aimed to cross over Stones and Sand.

I totally redesigned the Chassis of TB6 to make it more robust.

1st Video Shows it in Action. (-: towards the end are some Outakes :-)

2nd Video :- PolyMorph SkidSteer Helper ©



Here TB-007 has been fitted with a Wireless Camera -

so i can sit in my deck chair and watch its progress should it wander off.

The Camera is mounted to a servo which also has a Laser pointer attached (see main picture)  -

During "Fine Detect" phase of software loop, the servo positions itsself to look

and pinpoint with laser and Video the exact location of Metal Found.



The underside shows the layout of the Motors and a new PolyMorph SkidTurn Helper ©



Here is the  PolyMorph SkidTurn Helper © in more detail - In the Down Position.



 In the Up Position.

It is a hollow Poly-Morph "Thingy" which is connected to a servo - when activated it lifts the whole back end up into the air.

Then the front wheels can turn in opposite directions and the "Thingy" slides -

allowing TB-007 to turn effortlessly on the Spot - over the ground (polymorph is very smooth).



The BirdsNest (Thunder) ---- not so pretty but hey it works -

i have to install a second Voice Arduino so i have not finalised the layout

(-: velco straps are magic for rapid proto-typing :-)

TB-007 is Arduino Based with a Motor Shield (that controls the 2 main motors - 1 stepper motor and 3 Servos)



Here are TB-007s Test Coins -

The 5 Cent Silver American Indian coin known as the "Buffalo" is my Favorite.

The 500Lira (in video) and 10F (silver/bronze ringed) coins have the best detect signal.


The Metal Detect Electronics have be Hacked out of a Hand Held Metal Detector.


The Metal Detector consists of 2 separate detetor coils wound around a ferrite rod.

 The Circuit is a Beat Frequency Oscillator - able to detect metal and also live electrical cable.

  The Beat-frequency oscillator (BFO) is the simplest type of metal detector.

The basic beat-frequency metal detector employs two radio frequency oscillators which are tuned near the same frequency. The first is called the search oscillator and the other is called the reference oscillator.

The outputs of the two oscillators are fed into a mixer which produces a signal that contains the sum and difference frequency components. This signal is feed to a low-pass filter removing the harmonics. As long as the two oscillators are tuned to the same frequency, the output will have no signal.

When a metallic object disturbs the magnetic field of the search coil, the frequency of the search oscillator shifts slightly and the detector will produce a signal in the audio frequency range.




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what kind of chassis was this built on? im very new to this but would like to learn. maybe adapt an existing chassis from a RC car to start with?

Hi Gareth, 

My name is Nick Borg and i am a final student of National Diploma in Electrical & Eletronics here in Malta, and as my final project i am doing an Automotive Robot with Metal Detection, and to be totally honest i have a problem in building a good metal detector for my robot. Now i saw your TB-007 Metal Detector and i was impressed with it which i'll tell you GREAT JOB for that!! it looks that your metal detector is very good, now i have this question which i would like to ask you, can you help me in building my metal detector please?

Thanks in advance and hope to hear from you soon,

Nick Borg


For this project i used a very simple hand held metal detector..... the ones you can buy in DIY stores for detecting cables or studs behind walls.

I took it apart and used a multimeter to test the circuit randomly until i found a spot that altered when i brought metal near the detect probe..... this analog signal is then attached to the adc input of the arduino .......its reall as simple as that.

If i where to make the project again ..... i would buy a commercial Big metal detctor rehouse the coil and electronics and beef up the Robot Chassis 3X or so........ because theTB6 and TB7 project is still grabbing me and i am also interested in creating bigger version........

I will help as much as i can, i hope what i posted above clears the process i used ...... if you get stuck or want more input then beep me here of PM me...

Best Regards ........ Gareth

hey gereth can u just tell tht wt is d processor u used for ths robot....plz plz...i ll be very thankfull to u......

TB-007 (ThunderBird 7) is the Big Brother of  TB-6 & also  (first idea Blogged here)

I used 2 Arduinos :-

  • 1 for motor control , skid turn servo, laser,camera servo not to forget the metal detector signal processing.
  • 1 for the Audio speech processing. 

hi..its really wondering...im a final year engineering student  i would lik to do the same project..can u provide the details and circuit schematics how to start with...can u pls help me im new to robotics..but im interested..i did one line follower thats my oly experience...

can u post ur ideas at ramkumar1089@gmai.com 

   I saw this type on Ebay and was wondering if I am in the ballpark for a metal detector. Not expensive and small. As long as it puts out a dignal, I can figure how to digitise it somehow. I am thinking of getting a job for my nrewly released Mini Monster Boe Bot. It has 2 leftover I/) and could easily get a few more if needed for searching the ground instead of avoiding things. The hand held like the ons't they use in the airport seem a little big and the cheaper coil type the same thing. 


Yes this type of Metal Detector is in the right direction (-: and it is reasonable priced :-)

I suspect it has a similar coil system as the one i show in my pictures above.

I dont see any specs on it though - mine is only good at detecting <4cm - its worth checking before buying.

On my system i had to probe around the circuit board until i found the analoge signal - as most of these types of handhelds just give out a yes/no metal detected logic.

This guy is awesome! Show me the magic place you are getting ideas from! :)

i have a queastion what is the cheapest servo controller controlled from pc