need help in metal detector circuit!! urgent!

Thread Starter

haha

Joined Sep 13, 2010
4
i didnt do the PCB yet. Juz construct in project board. that is my constructed circuit and my inductor. That inductor can be function as a magnet but when i put it in my circuit and pass some metal through the inductor, the LED have no any respond.(No metal pass through- LED light up: when metal detected,lamp should be dim or switch off)
i am using vehicle loop detector circuit diagram from Internet. Welcome for any other circuit diagram for metal detector. i need the simple circuit.
the inductance generate by inductor r too small. i need something that can be detect the small toy metal car. My prototype cant be too big bcoz i am doing T junction traffic light, that each lane will consist 3 sensor circuit.

THX A LOT FOR UR ALL HELP!View attachment my metal detector circuit.pdf
 

SgtWookie

Joined Jul 17, 2007
22,230
Well, the original schematic calls for a 6' diameter loop with 4 turns of wire.

That would make an inductor of about 64uH.

You obviously need a much smaller loop.

If you used a form that was 3" in diameter, 18 turns of wire around it would also be about 64uH.

However, your big problem is that a vehicle has a LOT of metal in it, and will change the inductance of the big loop inductor by quite a bit. A little toy car made from "pot metal" will have almost no effect on it.
 

Thread Starter

haha

Joined Sep 13, 2010
4
ya.. so i will add a magnet in that toy car. may i know around how big the coil should be? how to know the value of inductance that sufficient to detect the metal?

thx
 

marshallf3

Joined Jul 26, 2010
2,358
ya.. so i will add a magnet in that toy car. may i know around how big the coil should be? how to know the value of inductance that sufficient to detect the metal?

thx
A magnet isn't the answer as there is no effect from the magnetism, it's the mass of ferrous metal that matters. A thin plate of steel would be better.

A lot of today's products are made from what's commonly referred to as pot metal which, by nature, isn't always all that ferrous:
http://en.wikipedia.org/wiki/Pot_metal
 
Top