Wednesday, July 30, 2014

METAL DETECTOR


Hello again.. This time I’m going to tell you how to make a very simple metal detector with a minimum cost. I made this with a group for a module of my degree program. The basic circuit we took from the internet and did some modifications according to my requirements.  For this we needed few devices as below.

NE555
47kΩ resister
2.2 μF, 3.3 μF, 10 μF capacitors
Speaker (8Ω resistance)
Copper wires of 0.3mm in diameter
9V battery
Switch
Connecting wires

Here we used a 555 IC and it gives accurate oscillations and these oscillations are controlled by the capacitor network and inductor used in the circuit. When the inductor goes near the metal the inductance change and frequency varies according to that. Therefore when the inductor meets a metal it gives out a different sound from the speaker.

This is the basic circuit for the metal detector and we changed few capacitor values from the original circuit.  



FIGURE 1: BASIC CIRCUIT

All the components like resisters, speaker, capacitors and IC can be obtained easily but when comes to the inductor it becomes more complex. When making the inductor we used copper wires with 0.3mm diameter. Then we wound the copper wire around circular rig foam for 200 turns. This rig foam circle has a diameter of 15cm and height of 1.5 cm. We got these values why doing few calculations and tests.

To find a suitable diameter for the inductor we used inductors with few different measurements and connected it to the above circuit and checked the accuracy by measuring output frequency. We found that with the increment of the diameter the accuracy also increasing. So we selected 15cm. Then we removed an inner circular portion from the rig form to make it air core and by using equation 1 below, we calculated the number of turns of the inductor.




L – Inductance
D – Diameter
N – Number of turns
H- Height

According to the circuit we could get 10mH inductance by 187 turns. But for better inductance we used 200 turns which gives an inductance of 11.5mH.


FIGURE 2: INDUCTOR

After making the inductor the circuit in Figure 1 can be connected to the project board and test it. We did not use PCB because this is a simple circuit. We made the circuit on a dot board as below.


FIGURE 3: CIRCUIT MOUNTED TO THE DOT BOARD

Now the basic metal detector is ready. To give a better finishing for the device we made a box with Perspex and attached the circuit on the dot board, batteries, switch  and speaker to that box.


FIGURE 4: COMPONENTS FIXED TO THE PERSPEX BOX

Then we connected this box to the wood handle of the detector and then we connected the inductor to a plastic plate and that plastic plate connected to a rod. 


FIGURE 4: PERSPEX BOX CONNECTED TO THE ROD


FIGURE 5: completed metal detector

This is a very simple metal detector and this can be improved in many aspects like technically, appearance etc.  Anyway from this post you can get the fundamental understanding about  a metal detector and let’s meet with another post soon. Thank you for reading..

Special thanx  to Sampath and Amila... 

9 comments:

  1. Buha ha ha. Bim bomba hoyannat puluwanda. Ela ela

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  2. Nice to see some one from Galle.....doing Electronics :)

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  3. Great Work Nishadi !!!!! (Y) keep it up :) :)

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  4. I have created metal detector for my A/L individual project in 2005. It works fine and i have used CD4011 for it . Now it seems about 10 years for that project . I have used headphones for heard the sound difference . It can detect 30cm down from the ground. Great go on!

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